Arabidopsis DELLA and JAZ proteins bind the WD-repeat/bHLH/MYB complex to modulate gibberellin and jasmonate signaling synergy

Molecular mechanism of SmMYB53 activates the expression of SmCYP71D375, thereby modulating tanshinone accumulation in Salvia miltiorrhiza

Tanshinones are bioactive diterpenoid chemicals of the herb Salvia miltiorrhiza with a characteristic furan D-ring. As a newly identified downstream enzyme, SmCYP71D375, catalyzes hydroxylation by 14,16-ether (hetero)cyclization to form the furan D-ring from the precursor of the phenolic abietane-type diterpenoids that exist widely in Lamiaceae plants. However, its transcriptional regulatory network, with SmCYP71D375 as the direct target gene, remains unclear. In the present study, the promoter of SmCYP71D375 was employed as the bait to mine the upstream regulatory protein using the cDNA yeast library of S. miltiorrhiza. An R2R3-MYB transcription factor gene, SmMYB53, was identified. Overexpressing SmMYB53 in transgenic hairy roots upregulated SmCYP71D375 expression, thereby accelerating tanshinone accumulation, whereas tanshinone accumulation was inhibited in SmMYB53-RNAi transgenic hairy root lines. To dissect the regulatory network of SmMYB53, SmbZIP51 was captured using SmMYB53 as the bait to prey for its potential interacting proteins in the cDNA yeast library. Yeast two-hybrid, glutathione S-transferase pull-down, and bimolecular fluorescence complementation assays were independently used to verify the interaction between the SmMYB53 and SmbZIP51 proteins . We further verified that the upregulation of SmCYP71D375 activated by SmMYB53 would be inhibited by the interaction of SmMYB53 and SmbZIP51. The present findings uncover the molecular regulatory network underlying SmCYP71D375 as the direct target regulating tanshinone biosynthesis and offer a basis for the genetic improvement of medicinal substance biosynthesis in S. miltiorrhiza.

Transcriptional landscape illustrates the diversified adaptation of medicinal plants to multifactorial stress combinations linked with high altitude

MAIN CONCLUSION

This study at high-altitude alpine environment reveals the molecular signatures associated with stress response and secondary metabolite accumulation, contributing to Picrorhiza kurroa adaptation, which is primarily regulated by a strong interplay of phytohormones. The high-altitude alpine environment is an extreme and variable environment with unique combinations of abiotic/biotic stresses. Despite progress about plant response to individual and combined abiotic stress in controlled conditions, our knowledge of plant adaptations to multifactorial stress combinations that typically occur in alpine environments is limiting. Here, we utilized the high-altitude medicinal herb Picrorhiza kurroa to investigate how multifactorial stress combinations prevailing along the high-altitude gradient at the western Himalayas affect gene expression and cellular pathways. Leaf transcriptional dynamics identified 7,388 differentially expressed unigenes (DEGs), highlighting unique gene expression patterns, specific pathways, and processes that play a crucial role in plant response to the complex micro-environment of high-altitude. Gene regulatory response largely relies on basic helix-loop-helix (bHLH), no apical meristem (NAC), and ethylene responsive factor (ERF) transcription factor families. Further, unigenes associated with secondary metabolism, multiple abiotic/biotic stress responses, and a variety of cellular and reproductive developmental processes were activated through complex cross-talk among plant hormonal signal transduction pathways. The weak correlation between gene expression and corresponding protein accumulation could predict stress-responsive protein abundance largely under different post-transcriptional/translational regulation. These findings recognize an array of new candidate genes for climate resilience, which would contribute to further our research on high-altitude alpine plant adaptations.

Sugar and anthocyanins: A scientific exploration of sweet signals and natural pigments

The presence of anthocyanins imparts vibrant hues to plants, whose biosynthesis and accumulation is a complex process and are influenced by numerous factors. In plants, sugar acts as a primary energy source and signaling molecule regulating anthocyanins biosynthesis. In this review, we provides a comprehensive overview of the relationship between sugar and anthocyanin. We delved into the intricate biosynthetic pathway of anthocyanins, outlining the key structural genes involved and their functions. Furthermore, we summarized how various environmental factors such as sugar, light, abiotic stresses, etc., affect anthocyanin biosynthesis. Notably, Most notably, we emphasized that sugars can independently regulate anthocyanin biosynthesis by modulating the expression of the MBW complex or structural genes, as well as through cascades involving hormones. These findings offer valuable insights into understanding the molecular mechanisms underlying anthocyanin accumulation and present potential avenues for enhancing anthocyanin content in plants through targeted manipulations that could have applications in agriculture and nutrition.

A review of the interaction mechanisms between jasmonic acid (JA) and various plant hormones, as well as the core regulatory role of MYC2

Jasmonic acid (JA), as a defensive plant hormone, can synergistically or antagonistically interact with common hormones such as gibberellin (GA), abscisic acid (ABA), indole-3-acetic hormone acid (IAA), and ethylene (ETH) during the plant growth process, as well as interact with hormones such as melatonin (MT), brassinolide (BR), and resveratrol to regulate plant growth and development processes such as metabolite synthesis, pest and disease defense, and organ growth. The core regulatory factor MYC2 of JA mainly mediates the signal transduction pathways of these hormone interactions by interacting with other genes or regulating transcription. This article reviews the mechanism of cross-talk between JA and hormones such as ABA, GA, and salicylic acid (SA), and discusses the role of MYC2 in hormone interactions.

CtMYB63 enhances the waterlogging tolerance of safflower through the JA signalling pathway

MeJA can help plants resist external stress, and waterlogging stress is the most serious stress for safflower. The mechanism by which MeJA (Methyl jasmonate) induction helps safflower resist waterlogging stress is unclear. Our results indicate that CtMYB63 responds to MeJA through the TGACG motif element, and MeJA induction can further increase the expression of CtMYB63. Under MeJA induction, CtMYB63 is expressed by regulating the transcriptional expression of CtDFR1, CtANS1 and CtANR1, thereby increasing the biomass and flavonoid content of safflower, but inhibiting plant elongation. Our waterlogging stress experiments further demonstrated that overexpression of CtMYB63 can enhance antioxidant enzyme activity to clear the accumulation of MDA (Malondialdehyde), H2O2, and O2-. We found that MeJA induction could further improve the waterlogging stress tolerance of overexpressed CtMYB63 and WT (wild-type) safflower. Still, the waterlogging tolerance of CtMYB63Δ was weakened due to the deletion of the TGACG motif element. Finally, we found through yeast one-hybrid (Y1H) and luciferase assays that CtMYB63 regulates the expression of downstream genes by binding to the promoters of downstream genes. However, CtJAZ9 inhibits the expression of downstream genes. In summary, our experiments show that CtMYB63 enhances the waterlogging tolerance of safflower through the JA signalling pathway, providing a new idea for improving safflower yield through molecular breeding.

The E3 ubiquitin ligase BRG3 and the protein kinase MPK7 antagonistically regulate LBD36 turnover, a key node for integrating nitrate and gibberellin signaling in apple

Nitrate is the main source of nitrogen in plants. Nitrate stimulation causes changes in plant secondary metabolites, including anthocyanins. However, the molecular mechanism underlying how nitrate regulates anthocyanin biosynthesis remains unclear. In this study, we identified a nitrate response factor MdLBD36 in apple. This factor positively regulated nitrate deficiency-induced anthocyanin biosynthesis by promoting the transcriptional activity of MdABI5, an important regulator of anthocyanins, and directly activated MdABI5 expression. The E3 ubiquitin ligase MdBRG3 promoted the ubiquitinated degradation of MdLBD36 to reduce anthocyanin biosynthesis under nitrate-sufficient conditions. Nitrate deficiency-activated MdMPK7 maintained the stimulating effect of MdLBD36 on anthocyanin biosynthesis by counteracting the MdBRG3-mediated degradation of MdLBD36. Nitrate coordinated gibberellin (GA) signaling to regulate anthocyanin biosynthesis. The GA signaling repressor MdRGL2a contributed to MdLBD36-promoted anthocyanin biosynthesis by enhancing the MdLBD36-MdABI5 interaction and increasing the MdLBD36 transcriptional activation of MdABI5. In summary, our results elucidate the molecular framework of the coordinated regulation of the nitrate signaling response and anthocyanin biosynthesis by ubiquitination and phosphorylation. This study revealed the cross talk between nitrate and GA signaling in the regulation of anthocyanin biosynthesis and provides references for an in-depth exploration of the nitrate signal transduction pathway and its interactions with hormones.

Positional mapping - constitutive purple trait locus (pl) in guava (Psidium guajava L.) in F2 and BC1F1 populations of Purple Local × Allahabad Safeda

Guava (Psidium guajava L.) is a popular fruit crop in Southeast Asia. Landrace Purple Local (PL), also known as Malaysian guava, is rich in anthocyanin content in all the plant parts but has poor yield. Genetic inheritance and physical location of the allele(s) controlling the constitutive purple trait in guava have not yet been reported. The F1 plants generated by cross hybridizing PL × green cv. Allahabad Safeda (AS) and analysed for 7 years did not exhibit purple trait. Evaluation of F1, F2 and BC1F1 populations derived from the cross between PL x AS revealed that purple color is a recessive trait in guava. Equally spaced (~10 Mb) co-dominant polymorphic markers developed by in silico analysis of AS and PL genome (mapped to AS genome assembly) into PCR-based assay mapped the purple color locus (pl) on pseudochromosome 11 (PC 11) of guava genome. Further mapping on PC 11 identified 2 InDel markers at 2.49 Mb (Pg11_INDL_2.49 M) and 4.99 Mb (Pg11_INDL_4.99 M) closely associated with pl. Also, QTLseqr for purple and non-purple bulks in F2 provided two co-localized significant peak ΔSNP-indices at positions 2489072 and 4978573 on PC 11. The mapped genomic interval harbours 85 coding genes, including the potential candidates MYB-like ETC1, anthocyanidin reductase, MYB41-like transcription factors and F-box protein SKIP27-like. Markers flanking pl would potentiate the marker-assisted introgression of anthocyanin trait in popular cultivars of guava.

Genome-wide analysis of basic helix-loop-helix (bHLH) transcription factors in petunia and identification of the putative candidate member involved in floral volatile benzenoids/phenylpropanoids metabolism

The basic helix-loop-helix (bHLH) family, a prominent group of transcription factors, is involved in plant growth, development, and secondary metabolic processes. Petunia (Petunia hybrida), a beloved and widely cultivated garden flower, boasts a diverse array of varieties, some of which exude a captivating fragrance that has garnered immense popularity. The aromatic allure of petunias primarily stems from the presence of volatile benzenoids/phenylpropanoids, the principal floral scent compounds. But whether bHLH transcription factors regulate petunia floral scent compound synthesis is not clear. In this study, we sought to screen the putative candidate member of bHLH which can be involved in the biosynthesis of benzenoids/phenylpropanoids by examining 63 members of the petunia bHLH gene family. Phylogenetic analysis of the 63 petunia bHLH proteins them into 16 subgroups. Almost all bHLH members contained alkaline/helix-loop-helix domains. Based on the reported RNA sequencing data of P. hybrida 'Mitchell', 30 assembled sequences were mapped to the bHLH genes of P. axillaris. Further qRT-PCR assays suggested that PhbHLH19 might be the putative candidate member in the biosynthesis of benzenoids/phenylpropanoids. PhbHLH19 showed higher expression levels in the petal limb but was lowly expressed at the bud stage, with a rapid increase in the expression level when flowers opened. The expression of PhbHLH19 displayed a significant positive correlation with that of PhPAL2, and the yeast one-hybrid assay verified that PhbHLH19 can bind to the promoter of PhPAL2. Moreover, a dual-luciferase assay proved the transcriptional activation of PhbHLH19 on PhPAL2. These findings suggested that PhbHLH19 might be a putative candidate in the regulation of benzenoid/phenylpropanoid synthesis by activating PhPAL2 expression.

MdZFP7 integrates JA and GA signals via interaction with MdJAZ2 and MdRGL3a in regulating anthocyanin biosynthesis and undergoes degradation by the E3 ubiquitin ligase MdBRG3

Jasmonic acid (JA) and gibberellin (GA) coordinate many aspects of plant growth and development, including anthocyanin biosynthesis. However, the crossover points of JA and GA signals and the pathways through which they interact to regulate anthocyanin biosynthesis are poorly understood. Here, we investigated the molecular mechanism by which the zinc finger protein (ZFP) transcription factor Malus domestica ZFP7 (MdZFP7) regulates anthocyanin biosynthesis by integrating JA and GA signals at the transcriptional and post-translational levels. MdZFP7 is a positive regulator of anthocyanin biosynthesis, which fulfills its role by directly activating the expression of MdMYB1 and enhancing the transcriptional activation of MdWRKY6 on the target genes MdDFR and MdUF3GT. MdZFP7 integrates JA and GA signals by interacting with the JA repressor apple JASMONATE ZIM-DOMAIN2 (MdJAZ2) and the GA repressor apple REPRESSOR-of-ga1-3-like 3a (MdRGL3a). MdJAZ2 weakens the transcriptional activation of MdMYB1 by MdZFP7 and disrupts the MdZFP7-MdWRKY6 interaction, thereby reducing the anthocyanin biosynthesis promoted by MdZFP7. MdRGL3a contributes to the stimulation of anthocyanin biosynthesis by MdZFP7 by sequestering MdJAZ2 from the MdJAZ2-MdZFP7 complex. The E3 ubiquitin ligase apple BOI-related E3 ubiquitin-protein ligase 3 (MdBRG3), which is antagonistically regulated by JA and GA, targets the ubiquitination degradation of MdZFP7. The MdBRG3-MdZFP7 module moves the crosstalk of JA and GA signals from the realm of transcriptional regulation and into the protein post-translational modification. In conclusion, this study not only elucidates the node-role of MdZFP7 in the integration of JA and GA signals, but also describes the transcriptional and post-translational regulatory network of anthocyanin biosynthesis with MdZFP7 as the hub.

Phosphorylation-dependent VaMYB4a regulates cold stress in grapevine by inhibiting VaPIF3 and activating VaCBF4

Cold stress severely impacts the quality and yield of grapevine (Vitis L.). In this study, we extend our previous work to elucidate the role and regulatory mechanisms of Vitis amurensis MYB transcription factor 4a (VaMYB4a) in grapevine's response to cold stress. Our results identified VaMYB4a as a key positive regulator of cold stress. We demonstrated that VaMYB4a undergoes phosphorylation by V. amurensis calcineurin B-like (CBL) proteins-interacting protein kinase 18 (VaCIPK18) under cold stress, a process that activates VaMYB4a transcriptional activity. Using chromatin immunoprecipitation sequencing (ChIP-seq). We performed a comprehensive genomic search to identify downstream components that interact with VaMYB4a, leading to the discovery of a basic helix-loop-helix transcription factor, V. amurensis phytochrome-interacting factor 3 (VaPIF3). VaMYB4a attenuated the transcriptional activity of VaPIF3 through a phosphorylation-dependent interaction under cold conditions. Furthermore, VaPIF3, which interacts with and inhibits V. amurensis C-repeat binding factor 4 (VaCBF4, a known positive regulator of cold stress), has its activity attenuated by VaMYB4a, which mediates the modulation of this pathway. Notably, VaMYB4a also interacted with and promoted the expression of VaCBF4 in a phosphorylation-dependent manner. Our study shows that VaMYB4a positively modulates cold tolerance in plants by simultaneously downregulating VaPIF3 and upregulating VaCBF4. These findings provide a nuanced understanding of the transcriptional response in grapevine under cold stress and contribute to the broader field of plant stress physiology.

Two novel alleles of the MYB transcription factor BjA06.GL1 and BjB02.GL1 control leaf trichomes and enhance resistance to aphids in Brassica juncea

Leaf trichome formation is a very important agronomic trait as it confers resistance to biotic and abiotic stresses, but the causal genes involved in this process in Brassica juncea remain largely unexplored. In this study, we first characterized the haplotypes of BjB02.GL1 among different inbred lines with leaf trichomes or glabrous leaves. A comparative analysis of the number and density of leaf trichomes between the two mustard inbred lines was then performed. BSA analysis of leaves with trichomes and glabrous pools from the F2 segregating population mapped the candidate genes on Chr.A06 and Chr.B02. Two candidate genes, BjA06.GL1 and BjB02.GL1, were subsequently cloned. After sequence alignment of the BjGL1 genes, both single-nucleotide polymorphisms (SNPs) and indel were identified in the BjA06.GL1 and BjB02.GL1 genes. And quantitative real-time polymerase chain reaction (qRT-PCR) analysis further confirmed that both the BjA06.GL1 and BjB02.GL1 genes were more highly expressed in leaves with trichomes than in glabrous leaves. As the leaf size increased, the leaf trichome density decreased. Gene editing of both BjA06.GL1 and BjB02.GL1 changed the leaf trichome to a glabrous leaf phenotype in mustard. In addition, plants with leaf trichomes presented greater resistance to aphids. Taken together, our results revealed that both BjA06.GL1 and BjB02.GL1 positively regulate leaf trichome formation and help increase aphid resistance in mustard. This study provides valuable resources and helps to elucidate the molecular mechanism of leaf trichome formation in B. juncea.

Flavonoids and anthocyanins in seagrasses: implications for climate change adaptation and resilience

Seagrasses are a paraphyletic group of marine angiosperms and retain certain adaptations from the ancestors of all embryophytes in the transition to terrestrial environments. Among these adaptations is the production of flavonoids, versatile phenylpropanoid secondary metabolites that participate in a variety of stress responses. Certain features, such as catalytic promiscuity and metabolon interactions, allow flavonoid metabolism to expand to produce novel compounds and respond to a variety of stimuli. As marine environments expose seagrasses to a unique set of stresses, these plants display interesting flavonoid profiles, the functions of which are often not completely clear. Flavonoids will likely prove to be effective and versatile agents in combating the new host of stress conditions introduced to marine environments by anthropogenic climate change, which affects marine environments differently from terrestrial ones. These new stresses include increased sulfate levels, changes in salt concentration, changes in herbivore distributions, and ocean acidification, which all involve flavonoids as stress response mechanisms, though the role of flavonoids in combatting these climate change stresses is seldom discussed directly in the literature. Flavonoids can also be used to assess the health of seagrass meadows through an interplay between flavonoid and simple phenolic levels, which may prove to be useful in monitoring the response of seagrasses to climate change. Studies focusing on the genetics of flavonoid metabolism are limited for this group, but the large chalcone synthase gene families in some species may provide an interesting topic of research. Anthocyanins are typically studied separately from other flavonoids. The phenomenon of reddening in certain seagrass species typically focuses on the importance of anthocyanins as a UV-screening mechanism, while the role of anthocyanins in cold stress is discussed less often. Both of these stress response functions would be useful for adaptation to climate change-induced deviations in tidal patterns and emersion. However, ocean warming will likely lead to a decrease in anthocyanin content, which may impact the performance of intertidal seagrasses. This review highlights the importance of flavonoids in angiosperm stress response and adaptation, examines research on flavonoids in seagrasses, and hypothesizes on the importance of flavonoids in these organisms under climate change.

Regulatory mechanisms of trichome and root hair development in Arabidopsis

In plants, cell fate determination is regulated temporally and spatially via a complex of signals consisting of a large number of genetic interactions. Trichome and root hair formation are excellent models for studying cell fate determination in plants. Nowadays, the mysteries underlying the reprograming of trichome and root hair and how nature programs the development of trichome and root hair is an interesting topic in the scientific field. In this review, we discuss the spatial and temporal regulatory networks and cross-talk between phytohormones and epigenetic modifications in the regulation of trichome and root hair initiation in Arabidopsis. The discussion in this review provides a good model for understanding the regulatory mechanism of cell differentiation processes in plants. Moreover, we summarize recent advances in the modulation of trichome and root hair initiation in plants and compare different regulatory mechanisms to help illuminate key goals for future research.

The transcription factor MfbHLH104 from Myrothamnus flabellifolia promotes drought tolerance of Arabidopsis thaliana by enhancing stability of the photosynthesis system

The resurrection plant Myrothamnus flabellifolia can survive extreme drought and desiccation conditions, and quickly recover after rewatering. However, little is known about the mechanism underlying the drought tolerance of M. flabellifolia. In this study, MfbHLH104 was cloned and introduced into Arabidopsis thaliana due to the lack of a transgenic system for M. flabellifolia. MfbHLH104 is localized in the nucleus. Its N-terminal region has transactivation ability in yeast, and the C-terminal region may inhibit the transactivation ability. Overexpressing MfbHLH104 significantly increased drought and salt tolerance of A. thaliana at both seedling and adult stages. It enhanced leaf water retention capacity by decreasing water loss rate and increasing drought- and abscisic acid (ABA) -induced stomatal closure. Additionally, it boosted osmolyte accumulation and ROS scavenging ability by up-regulating genes associated with osmolyte biosynthesis and antioxidant enzymes, and enhancing antioxidant enzyme activities. The expression of ABA-responsive genes were also promoted by MfbHLH104. Remarkably, RNA-seq analysis indicated that MfbHLH104 significantly up-regulated 32 genes (FDR < 0.05 and fold change ≥1.5) involved in photosynthesis related pathways (KEGG pathway No: ko00195, ko00196) under drought, which account for 18.7 % of the total up-regulated genes and the most enriched KEGG pathways. This result suggested that it may help to maintain the stability of the photosynthesis system under drought conditions.

Identification of male sterility-related genes in Saccharum officinarum and Saccharum spontaneum

KEY MESSAGE

Candidate male sterility genes were identified in sugarcane, which interacts with kinase-related proteins, transcription factors, and plant hormone signaling pathways to regulate stamen and anther development. Saccharum officinarum is a cultivated sugarcane species that its predominant feature is high sucrose content in stems. Flowering is necessary for breeding new cultivars but will terminate plant growth and reduce sugar yield. The wild sugarcane species Saccharum spontaneum has robust and viable pollen, whereas most S. officinarum accessions are male sterile, which is a desirable trait of a maternal parent in sugarcane breeding. To study male sterility and related regulatory pathways in sugarcane, we carried out RNAseq using flowers in different developmental stages between male-sterile S. officinarum accession 'LA Purple' and fertile S. spontaneum accession 'SES208'. Gene expression profiles were used to detect how genes are differentially expressed between male sterile and fertile flowers and to identify candidate genes for male sterility. Weighted gene correlation networks analysis (WGCNA) was conducted to investigate the regulatory networks. Transcriptomic analyses showed that 988 genes and 2888 alleles were differentially expressed in S. officinarum compared to S. spontaneum. Ten differentially expressed genes and thirty alleles were identified as candidate genes and alleles for male sterility in sugarcane. The gene Sspon.03G0007630 and two alleles of the gene Sspon.08G0002270, Sspon.08G0002270-2B and Sspon.08G0014700-1A, were involved in the early stamen or carpel development stages, while the remaining genes were classified into the post-meiosis stage. Gibberellin, auxin, and jasmonic acid signaling pathways are involved in the stamen development in sugarcane. The results expanded our knowledge of male sterility-related genes in sugarcane and generated genomic resources to facilitate the selection of ideal maternal parents to improve breeding efficiency.

Strigolactones Regulate Secondary Metabolism and Nitrogen/Phosphate Signaling in Tea Plants via Transcriptional Reprogramming and Hormonal Interactions

Strigolactones (SLs) are known to regulate plant architecture formation, nitrogen (N) and phosphorus (P) responses, and secondary metabolism, but their effects in tea plants remain unclear. We demonstrated that the application of a bioactive SL analogue GR24 either to tea roots or leaves initially stimulated but later inhibited catechins, theanine, and caffeine biosynthesis. GR24 treatment also promoted the accumulation of flavonols and insoluble proanthocyanidins in a time- and dose-dependent manner. GR24 influenced flavonoid and theanine biosynthesis genes, such as up-regulating CsTT2c, CsMYB12, and CsbZIP1, modulating N-responsive and assimilation genes (CsNRT1,1, CsGSI/TS1, CsHRS1, CsPHR1, CsNLA1, and CsLBD37/38/39), and repressing N/P transport and signaling genes (CsPHO2, CsPHT1s, CsNRT2,2, CsHHO1, and CsWRKY38). GR24-induced changes in secondary metabolites were also observed in the leaves of tea plants. GR24-regulated CsLBD37a interacted with CsTT8a and CsTT2c, repressing catechins biosynthesis by interrupting MBW complex formation. GR24 regulated caffeine biosynthesis and regulator genes CsS40 and CsNAC7 and may thereby suppress caffeine production. GR24 altered the transcriptomic profiles of multiple hormone biosynthesis and signaling genes that potentially regulate tea characteristic metabolism and N/P signaling. This study provides new insights into SL-induced transcriptional reprogramming that leads to changes in N/P nutrition, secondary metabolism, and hormone signaling in tea plants.

Microbe-Friendly Plants Enable Beneficial Interactions with Soil Rhizosphere Bacteria by Lowering Their Defense Responses

The use of plant growth-promoting rhizobacteria presents a promising addition to conventional mineral fertilizer use and an alternative strategy for sustainable agricultural crop production. However, genotypic variations in the plant host may result in variability of the beneficial effects from these plant-microbe interactions. This study examined growth promotion effects of commercial vegetable crop cultivars of tomato, cucumber and broccoli following application with five rhizosphere bacteria. Biochemical assays revealed that the bacterial strains used possess several nutrient acquisition traits that benefit plants, including nitrogen fixation, phosphate solubilization, biofilm formation, and indole-3-acetic acid (IAA) production. However, different host cultivars displayed genotype-specific responses from the inoculations, resulting in significant (p < 0.05) plant growth promotion in some cultivars but insignificant (p > 0.05) or no growth promotion in others. Gene expression profiling in tomato cultivars revealed that these cultivar-specific phenotypes are reflected in differential expressions of defense and nutrient acquisition genes, suggesting that plants can be categorized into "microbe-friendly" cultivars (with little or no defense responses against beneficial microbes) and "microbe-hostile" cultivars (with strong defense responses). These results validate the notion that "microbe-friendly" (positive interaction with rhizosphere microbes) should be considered an important trait in breeding programs when developing new cultivars which could result in improved crop yields.

Heterografting enhances chrysanthemum resistance to Alternaria alternata via jasmonate-mediated increases in trichomes and terpenoids

Trichomes are specialized hair-like structures in the epidermal cells of the above-ground parts of plants and help to protect them from pests and pathogens, and produce valuable metabolites. Chrysanthemum morifolium, which is used in tea products, has both ornamental and medicinal value; however, it is susceptible to infection by the fungus Alternaria alternata, which can result in substantial economic losses. Increasing the density of glandular trichomes enhances disease resistance and improves the production of medicinal metabolites in chrysanthemums, and jasmonate (JA) is known to promote the formation of trichomes in various plants. However, it remains unclear whether glandular trichomes in chrysanthemums are regulated by JA. In addition, grafting, a technique that can improve plant resistance to biotic stresses, has been poorly examined for its impact on glandular trichomes, terpenoids, and disease resistance. In this study, we demonstrate that grafting with Artemisia vulgaris rootstocks improves the resistance of chrysanthemum scions to A. alternata. Heterografted chrysanthemums exhibited higher trichome density and terpenoid content compared to self-grafted counterparts. Transcriptome analysis highlighted the significant role of CmJAZ1-like in disease resistance in heterografted chrysanthemums. Lines overexpressing CmJAZ1-like exhibited sensitivity to A. alternata, and this was characterized by reduced glandular trichome density and limited terpenoid content. Conversely, CmJAZ1-like silenced lines exhibited resistance to A. alternata and showed increased glandular trichome density and terpenoid content. Higher JA content was found in the heterografted chrysanthemum scions compared to self-grafted ones. Furthermore, we established that JA promoted the development of glandular trichomes and the synthesis of terpenoids while also inducing the degradation of CmJAZ1-like proteins in chrysanthemums. Our findings suggest that higher JA increases trichome density and terpenoid content, thereby enhancing resistance to A. alternata by regulating CmJAZ1-like in heterografted chrysanthemums.

Comparative analysis of element and hormone content in zygotic embryos of Pinus elliottii and P. elliottii × P. caribaea

Somatic embryogenesis is a crucial method for achieving clonal forestry in conifers. Understanding the development of zygotic embryos is essential not only for enhancing the efficiency and quality of somatic embryogenesis, but also for advancing forestry breeding programs. This study investigated dynamic changes of element and hormone contents during ZE development of Pinus elliottii and its hybrid P. elliottii × P. caribaea. Significant differences in embryo development speed among different clones were observed. Elemental analysis was conducted using inductively coupled plasma mass spectrometry (ICP-MS) and identified 68 elements, including major, minor, and beneficial elements. In both species, the contents of potassium (K), calcium (Ca), iron (Fe), boron (B) and five beneficial elements decreased during early ZE development, while phosphorus (P) and copper (Cu) increased. Significantly higher levels of K, Ca and Fe at the initial stage, and sulfur (S) and nickel (Ni) decreased at later stages were detected in P. elliottii than in the hybrid. For the other elements, except for very few significant differences at certain stages, most differences between the two species did not reach a significant level. The contents of endogenous hormones were determined and different accumulation patterns were detected in most hormones between the two species, except abscisic acid (ABA) which simultaneously decreased with developments by stage 8. Significant differences were found in indole-3-acetic acid (IAA) contents at most stages between species, while higher levels of total cytokinin (CK) at each stage were detected in the hybrid in comparison with those in P. elliottii. As a result, lower IAA to CK ratios in the hybrid than in P. elliottii. Methyl jasmonate (JA-me) and gibberellin A3 (GA3) contents showed a similar pattern and exhibited an M-shaped fluctuation in the hybrid. Furthermore, JA-me, GA3, gibberellin A4 (GA4) and brassinolide (BR) showed significantly higher levels in the hybrid than in P. elliottii. K-means clustering and correlation analyses were used to explore relationships between elements and hormones during embryo development, revealing complex interplay in both species. These data indicate different requirement in element and hormone contents for embryogenesis and suggest species-specific media composition for each step in somatic embryogenesis. The findings provide insights into their developmental processes and informing future research and applications in somatic embryogenesis and forestry breeding.

COI1 F-box proteins regulate DELLA protein levels, growth, and photosynthetic efficiency in maize

The F-box protein Coronatine Insensitive (COI) is a receptor for the jasmonic acid signaling pathway in plants. To investigate the functions of the 6 maize (Zea mays) COI proteins (COI1a, COI1b, COI1c, COI1d, COI2a, and COI2b), we generated single, double, and quadruple loss-of-function mutants. The pollen of the coi2a coi2b double mutant was inviable. The coi1 quadruple mutant (coi1-4x) exhibited shorter internodes, decreased photosynthesis, leaf discoloration, microelement deficiencies, and accumulation of DWARF8 and/or DWARF9, 2 DELLA family proteins that repress the gibberellic acid (GA) signaling pathway. Coexpression of COI and DELLA in Nicotiana benthamiana showed that the COI proteins trigger proteasome-dependent DELLA degradation. Many genes that are downregulated in the coi1-4x mutant are GA-inducible. In addition, most of the proteins encoded by the downregulated genes are predicted to be bundle sheath- or mesophyll-enriched, including those encoding C4-specific photosynthetic enzymes. Heterologous expression of maize Coi genes in N. benthamiana showed that COI2a is nucleus-localized and interacts with maize jasmonate zinc-finger inflorescence meristem domain (JAZ) proteins, the canonical COI repressor partners. However, maize COI1a and COI1c showed only partial nuclear localization and reduced binding efficiency to the tested JAZ proteins. Together, these results show the divergent functions of the 6 COI proteins in regulating maize growth and defense pathways.

A bHLH transcription factor AaMYC2-type positively regulates glandular trichome density and artemisinin biosynthesis in Artemisia annua

Artemisinin-based combinational therapies (ACTs) constitute the first line of malaria treatment. However, due to its trichome-specific biosynthesis, low concentration, and poor understanding of regulatory mechanisms involved in artemisinin biosynthesis and trichome development, it becomes very difficult to meet the increased demand for ACTs. Here, we have reported that a bHLH transcription factor, AaMYC2-type, plays an important role in regulating GST development and artemisinin biosynthesis in Artemisia annua. AaMYC2-type encodes a protein that is transcriptionally active and localised to the nucleus. It is prominently expressed in aerial parts like leaves, stems, inflorescence and least expressed in roots. AaMYC2-type expression is significantly increased under different hormonal treatments. In transgenic overexpression lines, AaMYC2-type OE, a significant increase in the expression of trichome development and artemisinin biosynthesis genes was observed. While in knockdown lines, Aamyc2-type, expression of trichome development and artemisinin biosynthesis genes were significantly reduced. Yeast one-hybrid assay clearly shows that the AaMYC2-type directly binds to the E-boxes in the promoter regions of ADS and CYP71AVI. The SEM microscopy depicted the number of trichomes elevated from 11 mm-2 in AaMYC2-type OE lines to 6.1 mm-2 in Aamyc2-type. The final effect of the alteration in biosynthetic and trichome developmental genes was observed in the accumulation of artemisinin. In the AaMYC2-type OE, the artemisinin content was 12 mg g-1DW, which was reduced to 3.2 mg g-1DW in the Aamyc2-type. Altogether, the above findings suggest that the AaMYC2-type play a dual regulating role in controlling both trichome developmental and artemisinin biosynthetic genes.

Advances in functional studies of plant MYC transcription factors

Myelocytomatosis (MYC) transcription factors (TFs) belong to the basic helix-loop-helix (bHLH) family in plants and play a central role in governing a wide range of physiological processes. These processes encompass plant growth, development, adaptation to biotic and abiotic stresses, as well as secondary metabolism. In recent decades, significant strides have been made in comprehending the multifaceted regulatory functions of MYCs. This advancement has been achieved through the cloning of MYCs and the characterization of plants with MYC deficiencies or overexpression, employing comprehensive genome-wide 'omics' and protein-protein interaction technologies. MYCs act as pivotal components in integrating signals from various phytohormones' transcriptional regulators to orchestrate genome-wide transcriptional reprogramming. In this review, we have compiled current research on the role of MYCs as molecular switches that modulate signal transduction pathways mediated by phytohormones and phytochromes. This comprehensive overview allows us to address lingering questions regarding the interplay of signals in response to environmental cues and developmental shift. It also sheds light on the potential implications for enhancing plant resistance to diverse biotic and abiotic stresses through genetic improvements achieved by plant breeding and synthetic biology efforts.

Defects in Glabrous 3 (GL3) functionality underlie the absence of trichomes in Brassica napus

Previously, expression of the Arabidopsis thaliana GLABRA3 (GL3) induced trichome formation in Brassica napus. GL3 orthologues were examined from glabrous (B. oleracea), semi-glabrous (B. napus), moderately hirsute (B. rapa), and very hirsute (B. villosa) Brassica species. Ectopic expression of BnGL3, BrGL3 alleles, or BvGL3 induced trichome formation in glabrous B. napus with the effect on trichome number commensurate with density in the original accessions. Chimeric GL3 proteins in which the B. napus amino terminal region, which interacts with MYB proteins, or the middle region, which interacts with the WD40 protein TTG1, was exchanged with corresponding regions from A. thaliana were as stimulatory to trichome production as AtGL3. Exchange of the carboxy-terminal region containing a bHLH domain and an ACT domain did not alter the trichome stimulatory activity, although modeling of the ACT domain identified differences that could affect GL3 dimerization. B. napus A- and C-genomes orthologues differed in their abilities to form homo- and heterodimers. Modeling of the amino-terminal region revealed a conserved domain that may represent the MYB factor binding pocket. This region interacted with the MYB factors GL1, CPC, and TRY, as well as with JAZ8, which is involved in jasmonic acid-mediated regulation of MYC-like transcription factors. Protein interaction studies indicated that GL1 interaction with GL3 from B. napus and A. thaliana may underlie the difference in their respective abilities to induce trichome formation.

Response of Elymus nutans Griseb. seedling physiology and endogenous hormones to drought and salt stress

Elymus nutans Griseb. (E. nutans), a pioneer plant for the restoration of high quality pasture and vegetation, is widely used to establish artificial grasslands and ecologically restore arid and salinized soils. To investigate the effects of drought stress and salt stress on the physiology and endogenous hormones of E. nutans seedlings, this experiment configured the same environmental water potential (0 (CK), - 0.04, - 0.14, - 0.29, - 0.49, - 0.73, and - 1.02 MPa) of PEG-6000 and NaCl stress to investigate the effects of drought stress and salt stress, respectively, on E. nutans seedlings under the same environmental water potential. The results showed that although the physiological indices and endogenous hormones of the E. nutans seedlings responded differently to drought stress and salt stress under the same environmental water potential, the physiological indices of E. nutans shoots and roots were comprehensively evaluated using the genus function method, and the physiological indices of the E. nutans seedlings under the same environmental water potential exhibited better salt tolerance than drought tolerance. The changes in endogenous hormones of the E. nutans seedlings under drought stress were analyzed to find that treatment with gibberellic acid (GA3), gibberellin A7 (GA7), 6-benzyladenine (6-BA), 6-(y,y-dimethylallylaminopurine) (2.IP), trans-zeatin (TZ), kinetin (KT), dihydrozeatin (DHZ), indole acetic acid (IAA), and 2,6-dichloroisonicotininc acid (INA) was more effective than those under drought stress. By analyzing the amplitude of changes in the endogenous hormones in E. nutans seedlings, the amplitude of changes in the contents of GA3, GA7, 6-BA, 2.IP, TZ, KT, DHZ, IAA, isopentenyl adenosine (IPA), indole-3-butyric acid (IBA), naphthalene acetic acid (NAA), and abscisic acid was larger in drought stress compared with salt stress, which could be because the endogenous hormones are important for the drought tolerance of E. nutans itself. The amplitude of the changes in the contents of DHZ, TZR, salicylic acid, and jasmonic acid was larger in salt stress compared with drought stress. Changes in the content of melatonin were larger in salt stress compared with drought stress, which could indicate that endogenous hormones and substances are important for the salt tolerance of E. nutans itself.

Chemical Driving the Subtype Selectivity of Phytohormone Receptors Is Beneficial for Crop Productivity

Chemicals that modulate phytohormones serve as a research tool in plant science and as products to improve crop productivity. Subtype selectivity refers to a ligand to selectively bind to specific subtypes of a receptor rather than binding to all possible subtypes indiscriminately. It allows for precise and specific control of cellular functions and is widely used in medicine. However, subtype selectivity is rarely mentioned in the realm of plant science, and it requires integrated knowledge from chemistry and biology, including structural features of small molecules as ligands, the redundancy of target proteins, and the response of signaling factors. Here, we present a comprehensive review and evaluation of phytohormone receptor subtype selectivity, leveraging the chemical characteristics of phytohormones and their analogues as clues. This work endeavors to provide a valuable research strategy that integrates knowledge from chemistry and biology to advance research efforts geared toward enhancing crop productivity.

Catechin promotes the germination of Pistacia chinensis seeds via GA biosynthesis

BACKGROUND AND AIMS

Chinese pistachio (Pistacia chinensis), an important horticultural plant species, holds great ornamental value with beautiful leaves and fruits. Seedling propagation of this tree species is restricted by its erratic seed germination; however, the germination mechanism is ambiguous. The aim of this study was to determine the germination mechanism from a novel perspective based on the multi-omics data.

METHODS

The multi-omics technique combined with hormone content measurement was applied to seed germination of Chinese pistachio.

KEY RESULTS

Due to its great accumulation during seed germination, catechin stood out from the identified metabolites in a broadly targeted metabolomic analysis. Exogenous catechin at 10 mg L-1 significantly improved the germination of Chinese pistachio seeds. An interesting result of hormone analysis was that the improving effect of catechin could be attributed to an increase in gibberellic acid 3 (GA3) content rather than a decrease in abscisic acid (ABA) content before germination. Treatments with paclobutrazol (PAC, a GA biosynthesis inhibitor) and PAC + catechin also showed that the promoting effect of catechin on seed germination depends on GA biosynthesis. Transcriptome analysis and qRT‒PCR further revealed that catechin induced the expression of PcGA20ox5 to activate GA biosynthesis. Several transcription factors were induced by catechin and GA treatments, such as TCP, bZIP and C3H, which may play an important regulatory role in GA biosynthesis in a catechin-mediated way.

CONCLUSIONS

Catechin promotes seed germination via GA biosynthesis in Chinese pistachios. This study proposes a novel mechanism by which catechin promotes seed germination via the GA pathway, which provides new insight into a comprehensive understanding of seed dormancy and germination.

Gossypium arboreum PPD2 facilitates root architecture development to increase plant resilience to salt stress

The jasmonic acid (JA) signaling pathway plays an important role in plant responses to abiotic stresses. The PEAPOD (PPD) and jasmonate ZIM-domain (JAZ) protein in the JA signaling pathway belong to the same family, but their functions in regulating plant defense against salt stress remain to be elucidated. Here, Gossypium arboreum PPD2 was overexpressed in Arabidopsis thaliana and systematically silenced in cotton for exploring its function in regulating plant defense to salt stress. The GaPPD2-overexpressed Arabidopsis thaliana plants significantly increased the tolerance to salt stress compared to the wild type in both medium and soil, while the GaPPD2-silenced cotton plants showed higher sensitivity to salt stress than the control in pots. The antioxidant activities experiment showed that GaPPD2 may mitigate the accumulation of reactive oxygen species by promoting superoxide dismutase accumulation, consequently improving plant resilience to salt stress. Through the exogenous application of MeJA (methy jasmonate) and the protein degradation inhibitor MG132, it was found that GaPPD2 functions in plant defense against salt stress and is involved in the JA signaling pathway. The RNA-seq analysis of GaPPD2-overexpressed A. thaliana plants and receptor materials showed that the differentially expressed genes were mainly enriched in antioxidant activity, peroxidase activity, and plant hormone signaling pathways. qRT-PCR results demonstrated that GaPPD2 might positively regulate plant defense by inhibiting GH3.2/3.10/3.12 expression and activating JAZ7/8 expression. The findings highlight the potential of GaPPD2 as a JA signaling component gene for improving the cotton plant resistance to salt stress and provide insights into the mechanisms underlying plant responses to environmental stresses.

GhWER controls fiber initiation and early elongation by regulating ethylene signaling pathway in cotton (Gossypium hirsutum)

Cotton fibers are specialized single-cell trichomes derived from epidermal cells, similar to root hairs and trichomes in Arabidopsis. While the MYB-bHLH-WD40 (MBW) complex has been shown to regulate initiation of both root hairs and trichomes in Arabidopsis, the role of their homologous gene in cotton fiber initiation remains unknown. In this study, we identified a R2R3 MYB transcription factor (TF), GhWER, which exhibited a significant increase in expression within the outer integument of ovule at -1.5 DPA (days post anthesis). Its expression peaked at -1 DPA and then gradually decreased. Knockout of GhWER using CRISPR technology inhibited the initiation and early elongation of fiber initials, resulting in the shorter mature fiber length. Additionally, GhWER interacted with two bHLH TF, GhDEL65 and GhbHLH121, suggesting a potential regulatory complex for fiber development. RNA-seq analysis of the outer integument of the ovule at -1.5 DPA revealed that the signal transduction pathways of ethylene, auxin and gibberellin were affected in the GhWER knockout lines. Further examination demonstrated that GhWER directly activated ethylene signaling genes, including ACS1 and ETR2. These findings highlighted the biological function of GhWER in regulating cotton fiber initiation and early elongation, which has practical significance for improving fiber quality and yield.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01477-6.

Harnessing Phytohormones: Advancing Plant Growth and Defence Strategies for Sustainable Agriculture

Phytohormones, pivotal regulators of plant growth and development, are increasingly recognized for their multifaceted roles in enhancing crop resilience against environmental stresses. In this review, we provide a comprehensive synthesis of current research on utilizing phytohormones to enhance crop productivity and fortify their defence mechanisms. Initially, we introduce the significance of phytohormones in orchestrating plant growth, followed by their potential utilization in bolstering crop defences against diverse environmental stressors. Our focus then shifts to an in-depth exploration of phytohormones and their pivotal roles in mediating plant defence responses against biotic stressors, particularly insect pests. Furthermore, we highlight the potential impact of phytohormones on agricultural production while underscoring the existing research gaps and limitations hindering their widespread implementation in agricultural practices. Despite the accumulating body of research in this field, the integration of phytohormones into agriculture remains limited. To address this discrepancy, we propose a comprehensive framework for investigating the intricate interplay between phytohormones and sustainable agriculture. This framework advocates for the adoption of novel technologies and methodologies to facilitate the effective deployment of phytohormones in agricultural settings and also emphasizes the need to address existing research limitations through rigorous field studies. By outlining a roadmap for advancing the utilization of phytohormones in agriculture, this review aims to catalyse transformative changes in agricultural practices, fostering sustainability and resilience in agricultural settings.

Highlights in gibberellin research: A tale of the dwarf and the slender

It has been almost a century since biologically active gibberellin (GA) was isolated. Here, we give a historical overview of the early efforts in establishing the GA biosynthesis and catabolism pathway, characterizing the enzymes for GA metabolism, and elucidating their corresponding genes. We then highlight more recent studies that have identified the GA receptors and early GA signaling components (DELLA repressors and F-box activators), determined the molecular mechanism of DELLA-mediated transcription reprograming, and revealed how DELLAs integrate multiple signaling pathways to regulate plant vegetative and reproductive development in response to internal and external cues. Finally, we discuss the GA transporters and their roles in GA-mediated plant development.

Genetic interaction between TTG2 and AtPLC1 reveals a role for phosphoinositide signaling in a co-regulated suite of Arabidopsis epidermal pathways

The TTG2 transcription factor of Arabidopsis regulates a set of epidermal traits, including the differentiation of leaf trichomes, flavonoid pigment production in cells of the inner testa (or seed coat) layer and mucilage production in specialized cells of the outer testa layer. Despite the fact that TTG2 has been known for over twenty years as an important regulator of multiple developmental pathways, little has been discovered about the downstream mechanisms by which TTG2 co-regulates these epidermal features. In this study, we present evidence of phosphoinositide lipid signaling as a mechanism for the regulation of TTG2-dependent epidermal pathways. Overexpression of the AtPLC1 gene rescues the trichome and seed coat phenotypes of the ttg2-1 mutant plant. Moreover, in the case of seed coat color rescue, AtPLC1 overexpression restored expression of the TTG2 flavonoid pathway target genes, TT12 and TT13/AHA10. Consistent with these observations, a dominant AtPLC1 T-DNA insertion allele (plc1-1D) promotes trichome development in both wild-type and ttg2-3 plants. Also, AtPLC1 promoter:GUS analysis shows expression in trichomes and this expression appears dependent on TTG2. Taken together, the discovery of a genetic interaction between TTG2 and AtPLC1 suggests a role for phosphoinositide signaling in the regulation of trichome development, flavonoid pigment biosynthesis and the differentiation of mucilage-producing cells of the seed coat. This finding provides new avenues for future research at the intersection of the TTG2-dependent developmental pathways and the numerous molecular and cellular phenomena influenced by phospholipid signaling.

Integrative Metabolomic and Transcriptomic Analysis Elucidates That the Mechanism of Phytohormones Regulates Floral Bud Development in Alfalfa

Floral bud growth influences seed yield and quality; however, the molecular mechanism underlying the development of floral buds in alfalfa (Medicago sativa) is still unclear. Here, we comprehensively analyzed the transcriptome and targeted metabolome across the early, mid, and late bud developmental stages (D1, D2, and D3) in alfalfa. The metabolomic results revealed that gibberellin (GA), auxin (IAA), cytokinin (CK), and jasmonic acid (JA) might play an essential role in the developmental stages of floral bud in alfalfa. Moreover, we identified some key genes associated with GA, IAA, CK, and JA biosynthesis, including CPS, KS, GA20ox, GA3ox, GA2ox, YUCCA6, amid, ALDH, IPT, CYP735A, LOX, AOC, OPR, MFP2, and JMT. Additionally, many candidate genes were detected in the GA, IAA, CK, and JA signaling pathways, including GID1, DELLA, TF, AUX1, AUX/IAA, ARF, GH3, SAUR, AHP, B-ARR, A-ARR, JAR1, JAZ, and MYC2. Furthermore, some TFs related to flower growth were screened in three groups, such as AP2/ERF-ERF, MYB, MADS-M-type, bHLH, NAC, WRKY, HSF, and LFY. The findings of this study revealed the potential mechanism of floral bud differentiation and development in alfalfa and established a theoretical foundation for improving the seed yield of alfalfa.

Characterization and expression analysis of GLABRA3 (GL3) genes in cotton: insights into trichome development and hormonal regulation

BACKGROUND

GLABRA3 (GL3) and ENHANCER OF GLABRA3 (EGL3) genes encode a typical helix-loop-helix (bHLH) transcription factors that primarily regulate trichome branching and root hair development, DNA endoreduplication, trichoblast size, and stomatal formation. The functions of GL3 genes in cotton crop have been poorly characterized. In this study, we performed comprehensive genome-wide scans for GL3 and EGL3 homologs to enhance our comprehension of their potential roles in trichome and fiber development in cotton crop.

METHODS AND RESULTS

Our findings paraded that Gossypium hirsutum and G. barbadense have 6 GL3s each, unevenly distributed on 4 chromosomes whereas, G. arboreum, and G. raimondii have 3 GL3s each, unevenly distributed on 2 chromosomes. Gh_A08G2088 and Gb_A09G2187, despite having the same bHLH domain as the other GL3 genes, were excluded due to remarkable short sequences and limited number of motifs, indicating a lack of potential functional activity. The phylogenetic analysis categorized remaining 16 GL3s into three subfamilies (Group I-III) closely related to A. thaliana. The 16 GL3s have complete bHLH domain, encompassing 590-631 amino acids, with molecular weights (MWs) ranging from 65.92 to 71.36 kDa. Within each subfamily GL3s depicted shared similar gene structures and motifs, indicating conserved characteristics within respective groups. Promoter region analysis revealed 27 cis-acting elements, these elements were responsive to salicylic acid, abscisic acid (ABA), methyl jasmonate (MeJA), and gibberellin. The expression of GL3 genes was analyzed across 12 tissues in both G. barbadense and G. hirsutum using the publicly available RNA-seq data. Among GL3s, Gb_D11G0219, Gb_D11G0214, and Gb_D08G2182, were identified as relatively highly expressed across different tissues, consequently selected for hormone treatment and expression validation in G. barbadense. RT-qPCR results demonstrated significant alterations in the expression levels of Gb_D11G0219 and Gb_D11G0214 following MeJA, GA, and ABA treatment. Subcellular localization prediction revealed that most GL3 proteins were predominantly expressed in the nucleus, while a few were localized in the cytoplasm and chloroplasts.

CONCLUSIONS

In summary, this study lays the foundation for subsequent functional validation of GL3 genes by identifying hormonal regulation patterns and probable sites of action in cotton trichome formation and fiber development. The results stipulate a rationale to elucidate the roles and regulatory mechanisms of GL3 genes in the intricate process of cotton fibre and trichome development.

The MYC2-PUB22-JAZ4 module plays a crucial role in jasmonate signaling in tomato

Jasmonates (JAs), a class of lipid-derived stress hormones, play a crucial role across an array of plant physiological processes and stress responses. Although JA signaling is thought to rely predominantly on the degradation of specific JAZ proteins by SCFCOI1, it remains unclear whether other pathways are involved in the regulation of JAZ protein stability. Here, we report that PUB22, a plant U-box type E3 ubiquitin ligase, plays a critical role in the regulation of plant resistance against Helicoverpa armigera and other JA responses in tomato. Whereas COI1 physically interacts with JAZ1/2/5/7, PUB22 physically interacts with JAZ1/3/4/6. PUB22 ubiquitinates JAZ4 to promote its degradation via the 26S proteasome pathway. Importantly, we observed that pub22 mutants showreduced resistance to H. armigera, whereas jaz4 single mutants and jaz1 jaz3 jaz4 jaz6 quadruple mutants have enhanced resistance. The hypersensitivity of pub22 mutants to herbivores could be partially rescued by JAZ4 mutation. Moreover, we found that expression of PUB22 can be transcriptionally activated by MYC2, thus forming a positive feedback circuit in JA signaling. We noticed that the PUB22-JAZ4 module also regulates other JA responses, including defense against B. cinerea, inhibition of root elongation, and anthocyanin accumulation. Taken together, these results indicate that PUB22 plays a crucial role in plant growth and defense responses, together with COI1-regulated JA signaling, by targeting specific JAZs.

Identification of bZIP Transcription Factors That Regulate the Development of Leaf Epidermal Cells in Arabidopsis thaliana by Single-Cell RNA Sequencing

Epidermal cells are the main avenue for signal and material exchange between plants and the environment. Leaf epidermal cells primarily include pavement cells, guard cells, and trichome cells. The development and distribution of different epidermal cells are tightly regulated by a complex transcriptional regulatory network mediated by phytohormones, including jasmonic acid, and transcription factors. How the fate of leaf epidermal cells is determined, however, is still largely unknown due to the diversity of cell types and the complexity of their regulation. Here, we characterized the transcriptional profiles of epidermal cells in 3-day-old true leaves of Arabidopsis thaliana using single-cell RNA sequencing. We identified two genes encoding BASIC LEUCINE-ZIPPER (bZIP) transcription factors, namely bZIP25 and bZIP53, which are highly expressed in pavement cells and early-stage meristemoid cells. Densities of pavement cells and trichome cells were found to increase and decrease, respectively, in bzip25 and bzip53 mutants, compared with wild-type plants. This trend was more pronounced in the presence of jasmonic acid, suggesting that these transcription factors regulate the development of trichome cells and pavement cells in response to jasmonic acid.

Cytokinin promotes anthocyanin biosynthesis via regulating sugar accumulation and MYB113 expression in Eucalyptus

Anthocyanins are flavonoid-like substances that play important roles in plants' adaptation to various environmental stresses. In this research, we discovered that cytokinin (CK) alone could effectively induce the anthocyanin biosynthesis in Eucalyptus and many other perennial woody plant species, but not in tobacco and Arabidopsis, suggesting a diverse role of CK in regulating anthocyanin biosynthesis in different species. Transcriptomic and metabolomic strategies were used to further clarify the specific role of CK in regulating anthocyanin biosynthesis in Eucalyptus. The results showed that 801 and 2241 genes were differentially regulated at 6 and 24 h, respectively, after CK treatment. Pathway analysis showed that most of the differentially expressed genes were categorized into pathways related to cellular metabolism or transport of metabolites, including amino acids and sugars. The metabolomic results well supported the transcriptome data, which showed that most of the differentially regulated metabolites were related to the metabolism of sugar, amino acids and flavonoids. Moreover, CK treatment significantly induced the accumulation of sucrose in the CK-treated leaves, while sugar starvation mimicked by either defoliation or shading treatment of the basal leaves significantly reduced the sugar increase of the CK-treated leaves and thus inhibited CK-induced anthocyanin biosynthesis. The results of in vitro experiment also suggested that CK-induced anthocyanin in Eucalyptus was sugar-dependent. Furthermore, we identified an early CK-responsive transcription factor MYB113 in Eucalyptus, the expression of which was significantly upregulated by CK treatment in Eucalyptus, but was inhibited in Arabidopsis. Importantly, the overexpression of EgrMYB113 in the Eucalyptus hairy roots was associated with significant anthocyanin accumulation and upregulation of most of the anthocyanin biosynthetic genes. In conclusion, our study demonstrates a key role of CK in the regulation of anthocyanin biosynthesis in Eucalyptus, providing a molecular basis for further understanding the regulatory mechanism and diversity of hormone-regulated anthocyanin biosynthesis in different plant species.

MdbHLH162 connects the gibberellin and jasmonic acid signals to regulate anthocyanin biosynthesis in apple

Anthocyanins are secondary metabolites induced by environmental stimuli and developmental signals. The positive regulators of anthocyanin biosynthesis have been reported, whereas the anthocyanin repressors have been neglected. Although the signal transduction pathways of gibberellin (GA) and jasmonic acid (JA) and their regulation of anthocyanin biosynthesis have been investigated, the cross-talk between GA and JA and the antagonistic mechanism of regulating anthocyanin biosynthesis remain to be investigated. In this study, we identified the anthocyanin repressor MdbHLH162 in apple and revealed its molecular mechanism of regulating anthocyanin biosynthesis by integrating the GA and JA signals. MdbHLH162 exerted passive repression by interacting with MdbHLH3 and MdbHLH33, which are two recognized positive regulators of anthocyanin biosynthesis. MdbHLH162 negatively regulated anthocyanin biosynthesis by disrupting the formation of the anthocyanin-activated MdMYB1-MdbHLH3/33 complexes and weakening transcriptional activation of the anthocyanin biosynthetic genes MdDFR and MdUF3GT by MdbHLH3 and MdbHLH33. The GA repressor MdRGL2a antagonized MdbHLH162-mediated inhibition of anthocyanins by sequestering MdbHLH162 from the MdbHLH162-MdbHLH3/33 complex. The JA repressors MdJAZ1 and MdJAZ2 interfered with the antagonistic regulation of MdbHLH162 by MdRGL2a by titrating the formation of the MdRGL2a-MdbHLH162 complex. Our findings reveal that MdbHLH162 integrates the GA and JA signals to negatively regulate anthocyanin biosynthesis. This study provides new information for discovering more anthocyanin biosynthesis repressors and explores the cross-talk between hormone signals.

SlPHL1 positively modulates acid phosphatase in response to phosphate starvation by directly activating the genes SlPAP10b and SlPAP15 in tomato

Increased acid phosphatase (APase) activity is a prominent feature of tomato (Solanum lycopersicum) responses to inorganic phosphate (Pi) restriction. SlPHL1, a phosphate starvation response (PHR) transcription factor, has been identified as a positive regulator of low Pi (LP)-induced APase activity in tomato. However, the molecular mechanism underlying this regulation remains to be elucidated. Here, SlPHL1 was found to positively regulate the LP-induced expression of five potential purple acid phosphatase (PAP) genes, namely SlPAP7, SlPAP10b, SlPAP12, SlPAP15, and SlPAP17b. Furthermore, we provide evidence that SlPHL1 can stimulate transcription of these five genes by binding directly to the PHR1 binding sequence (P1BS) located on their promoters. The P1BS mutation notably weakened SlPHL1 binding to the promoters of SlPAP7, SlPAP12, and SlPAP17b but almost completely abolished SlPHL1 binding to the promoters of SlPAP10b and SlPAP15. As a result, the transcriptional activation of SlPHL1 on SlPAP10b and SlPAP15 was substantially diminished. In addition, not only did transient overexpression of either SlPAP10b or SlPAP15 in tobacco leaves increase APase activity, but overexpression of SlPAP15 in Arabidopsis and tomato also increased APase activity and promoted plant growth. Subsequently, two SPX proteins, SlSPX1 and SlSPX4, were shown to physically interact with SlPHL1. Moreover, SlSPX1 inhibited the transcriptional activation of SlPHL1 on SlPAP10b and SlPAP15 and negatively regulated the activity of APase. Taken together, these results demonstrate that SlPHL1-mediated LP signaling promotes APase activity by activating the transcription of SlPAP10b and SlPAP15, which may provide valuable insights into the mechanisms of tomato response to Pi-limited stress.

Jasmonates, gibberellins, and powdery mildew modify cell cycle progression and evoke differential spatiotemporal responses along the barley leaf

Barley (Hordeum vulgare) is an important cereal crop, and its development, defence, and stress responses are modulated by different hormones including jasmonates (JAs) and the antagonistic gibberellins (GAs). Barley productivity is severely affected by the foliar biotrophic fungal pathogen Blumeria hordei. In this study, primary leaves were used to examine the molecular processes regulating responses to methyl-jasmonate (MeJA) and GA to B. hordei infection along the leaf axis. Flow cytometry, microscopy, and spatiotemporal expression patterns of genes associated with JA, GA, defence, and the cell cycle provided insights on cell cycle progression and on the gradient of susceptibility to B. hordei observed along the leaf. Notably, the combination of B. hordei with MeJA or GA pre-treatment had a different effect on the expression patterns of the analysed genes compared to individual treatments. MeJA reduced susceptibility to B. hordei in the proximal part of the leaf blade. Overall, distinctive spatiotemporal gene expression patterns correlated with different degrees of cell proliferation, growth capacity, responses to hormones, and B. hordei infection along the leaf. Our results highlight the need to further investigate differential spatial and temporal responses to pathogens at the organ, tissue, and cell levels in order to devise effective disease control strategies in crops.

The R2R3-MYB transcription factor OfMYB21 positively regulates linalool biosynthesis in Osmanthus fragrans flowers

Osmanthus fragrans is a well-known landscape ornamental tree species for its pleasing floral fragrance and abundance of flowers. Linalool, the core floral volatiles of O. fragrans, has tremendous economic value in the pharmaceuticals, cleaning products and cosmetics industries. However, the transcriptional regulatory network for the biosynthesis of linalool in O. fragrans remains unclear. Here, OfMYB21, a potential transcription factor regulating the linalool synthetase OfTPS2, was identified using RNA-seq data and qRT-PCR analysis. Yeast one-hybrid, dual-luciferase and EMSA showed that OfMYB21 directly binds to the promoter of OfTPS2 and activates its expression. Overexpression of OfMYB21 in the petals of O. fragrans led to up-regulation of OfTPS2 and increased accumulation of linalool, while silencing of OfMYB21 led to down-regulation of OfTPS2 and decreased biosynthesis of linalool. Subsequently, yeast two-hybrid, pull-down and BiFC experiments showed that OfMYB21 interacts with JA signaling factors OfJAZ2/3 and OfMYC2. Interestingly, the interaction between OfMYC2 and OfMYB21 further enhanced the transcription of OfTPS2, whereas OfJAZ3 attenuated this effect. Overall, our studies provided novel finding on the regulatory mechanisms responsible for the biosynthesis of the volatile monoterpenoid linalool in O. fragrans.

Transcription factors TgbHLH95 and TgbZIP44 cotarget terpene biosynthesis gene TgGPPS in Torreya grandis nuts

Terpenes are volatile compounds responsible for aroma and the postharvest quality of commercially important xiangfei (Torreya grandis) nuts, and there is interest in understanding the regulation of their biosynthesis. Here, a transcriptomics analysis of xiangfei nuts after harvest identified 156 genes associated with the terpenoid metabolic pathway. A geranyl diphosphate (GPP) synthase (TgGPPS) involved in production of the monoterpene precursor GPP was targeted for functional characterization, and its transcript levels positively correlated with terpene levels. Furthermore, transient overexpression of TgGPPS in tobacco (Nicotiana tabacum) leaves or tomato (Solanum lycopersicum) fruit led to monoterpene accumulation. Analysis of differentially expressed transcription factors identified one basic helix-loop-helix protein (TgbHLH95) and one basic leucine zipper protein (TgbZIP44) as potential TgGPPS regulators. TgbHLH95 showed significant transactivation of the TgGPPS promoter, and its transient overexpression in tobacco leaves led to monoterpene accumulation, whereas TgbZIP44 directly bound to an ACGT-containing element in the TgGPPS promoter, as determined by yeast 1-hybrid test and electrophoretic mobility shift assay. Bimolecular fluorescence complementation, firefly luciferase complementation imaging, co-immunoprecipitation, and GST pull-down assays confirmed a direct protein-protein interaction between TgbHLH95 and TgbZIP44 in vivo and in vitro, and in combination these proteins induced the TgGPPS promoter up to 4.7-fold in transactivation assays. These results indicate that a TgbHLH95/TgbZIP44 complex activates the TgGPPS promoter and upregulates terpene biosynthesis in xiangfei nuts after harvest, thereby contributing to its aroma.

Brassinosteroid signaling regulator BIM1 integrates brassinolide and jasmonic acid signaling during cold tolerance in apple

Although brassinolide (BR) and jasmonic acid (JA) play essential roles in the regulation of cold stress responses, the molecular basis of their crosstalk remains elusive. Here, we show a key component of BR signaling in apple (Malus × domestica), BR INSENSITIVE1 (BRI1)-EMS-SUPPRESSOR1 (BES1)-INTERACTING MYC-LIKE PROTEIN1 (MdBIM1), increases cold tolerance by directly activating expression of C-REPEAT BINDING FACTOR1 (MdCBF1) and forming a complex with C-REPEAT BINDING FACTOR2 (MdCBF2) to enhance MdCBF2-activated transcription of cold-responsive genes. Two repressors of JA signaling, JAZMONATE ZIM-DOMAIN1 (MdJAZ1) and JAZMONATE ZIM-DOMAIN2 (MdJAZ2), interact with MdBIM1 to integrate BR and JA signaling under cold stress. MdJAZ1 and MdJAZ2 reduce MdBIM1-promoted cold stress tolerance by attenuating transcriptional activation of MdCBF1 expression by MdBIM1 and interfering with the formation of the MdBIM1-MdCBF2 complex. Furthermore, the E3 ubiquitin ligase ARABIDOPSIS TÓXICOS en LEVADURA73 (MdATL73) decreases MdBIM1-promoted cold tolerance by targeting MdBIM1 for ubiquitination and degradation. Our results not only reveal crosstalk between BR and JA signaling mediated by a JAZ-BIM1-CBF module but also provide insights into the posttranslational regulatory mechanism of BR signaling.

Jasmonate signaling drives defense responses against Alternaria alternata in chrysanthemum

BACKGROUND

Black spot disease caused by the necrotrophic fungus Alternaria spp. is one of the most devastating diseases affecting Chrysanthemum morifolium. There is currently no effective way to prevent chrysanthemum black spot.

RESULTS

We revealed that pre-treatment of chrysanthemum leaves with the methy jasmonate (MeJA) significantly reduces their susceptibility to Alternaria alternata. To understand how MeJA treatment induces resistance, we monitored the dynamics of metabolites and the transcriptome in leaves after MeJA treatment following A. alternata infection. JA signaling affected the resistance of plants to pathogens through cell wall modification, Ca2+ regulation, reactive oxygen species (ROS) regulation, mitogen-activated protein kinase cascade and hormonal signaling processes, and the accumulation of anti-fungal and anti-oxidant metabolites. Furthermore, the expression of genes associated with these functions was verified by reverse transcription quantitative PCR and transgenic assays.

CONCLUSION

Our findings indicate that MeJA pre-treatment could be a potential orchestrator of a broad-spectrum defense response that may help establish an ecologically friendly pest control strategy and offer a promising way of priming plants to induce defense responses against A. alternata.

MdVQ10 promotes wound-triggered leaf senescence in association with MdWRKY75 and undergoes antagonistic modulation of MdCML15 and MdJAZs in apple

Wounding stress leads to leaf senescence. However, the underlying molecular mechanism has not been elucidated. In this study, we investigated the role of the MdVQ10-MdWRKY75 module in wound-induced leaf senescence. MdWRKY75 was identified as a key positive modulator of wound-induced leaf senescence by activating the expression of the senescence-associated genes MdSAG12 and MdSAG18. MdVQ10 interacted with MdWRKY75 to enhance MdWRKY75-activated transcription of MdSAG12 and MdSAG18, thereby promoting leaf senescence triggered by wounding. In addition, the calmodulin-like protein MdCML15 promoted MdVQ10-mediated leaf senescence by stimulating the interaction between MdVQ10 and MdWRKY75. Moreover, the jasmonic acid signaling repressors MdJAZ12 and MdJAZ14 antagonized MdVQ10-mediated leaf senescence by weakening the MdVQ10-MdWRKY75 interaction. Our results demonstrate that the MdVQ10-MdWRKY75 module is a key modulator of wound-induced leaf senescence and provides insights into the mechanism of leaf senescence caused by wounding.

Sl-lncRNA47980, a positive regulator affects tomato resistance to Phytophthora infestans

Emerging evidence suggests that long non-coding RNAs (lncRNAs) involve in defense respond against pathogen attack and show great potentials to improve plant resistance. Tomato late blight, a destructive plant disease, is caused by the oomycete pathogen Phytophthora infestans, which seriously affects the yield and quality of tomato. Our previous research has shown that Sl-lncRNA47980 is involved in response to P. infestans infection, but its molecular mechanism is unknown. Gain- and loss-of-function experiments revealed that Sl-lncRNA47980 as a positive regulator, played a crucial role in enhancing tomato resistance to P. infestans. The Sl-lncRNA47980-overexpressing transgenic plants exhibited an improved ability to scavenge reactive oxygen species (ROS), decreased contents of endogenous gibberellin (GA) and salicylic acid (SA), and increased contents of jasmonic acid (JA), while silencing of Sl-lncRNA47980 showed an opposite trend in the levels of these hormones. Furthermore, it was found that Sl-lncRNA47980 could upregulate the expression of SlGA2ox4 gene through activation of the promoter of SlGA2ox4 to affect GA content. The increased expression of the tomato GA signaling repressor SlDELLA could activate JA-related genes and inhibit SA-related genes to varying degrees respectively. In addition, exogenous application of GA3 and GA synthesis inhibitor uniconazole could increase disease susceptibility of Sl-lncRNA47980-overexpressing plants and the resistance of Sl-lncRNA47980-silenced plants, respectively, to P. infestans. From thus, it was speculated that Sl-lncRNA47980 conferred tomato resistance to P. infestans, which was related to the decrease in endogenous GA content. Our study provided information to link Sl-lncRNA47980 with changes in ROS accumulation and phytohormone levels in plant immunity, thus providing a new candidate gene for tomato breeding.

Genome-wide identification and bioinformatics analysis of the WD40 transcription factor family and candidate gene screening for anthocyanin biosynthesis in Rhododendron simsii

WD40 transcription factors (TFs) constitute a large gene family in eukaryotes, playing diverse roles in cellular processes. However, their functions in the major ornamental plant, Rhododendron simsii, remain poorly understood. In this study, we identified 258 WD40 proteins in the R. simsii genome, which exhibited an uneven distribution across chromosomes. Based on domain compositions and phylogenetic analysis, we classified these 258 RsWD40 proteins into 42 subfamilies and 47 clusters. Comparative genomic analysis suggested that the expansion of the WD40 gene family predates the divergence of green algae and higher plants, indicating an ancient origin. Furthermore, by analyzing the duplication patterns of RsWD40 genes, we found that transposed duplication played a major role in their expansion. Notably, the majority of RsWD40 gene duplication pairs underwent purifying selection during evolution. Synteny analysis identified significant orthologous gene pairs between R. simsii and Arabidopsis thaliana, Oryza sativa, Vitis vinifera, and Malus domestica. We also investigated potential candidate genes involved in anthocyanin biosynthesis during different flower development stages in R. simsii using RNA-seq data. Specifically, we identified 10 candidate genes during the bud stage and 7 candidate genes during the full bloom stage. GO enrichment analysis of these candidate genes revealed the potential involvement of the ubiquitination process in anthocyanin biosynthesis. Overall, our findings provide a valuable foundation for further investigation and functional analysis of WD40 genes, as well as research on the molecular mechanisms underlying anthocyanin biosynthesis in Rhododendron species.

Hormonal regulation of anthocyanin biosynthesis for improved stress tolerance in plants

Due to unprecedented climate change, rapid industrialization and increasing use of agrochemicals, abiotic stress, such as drought, low temperature, high salinity and heavy metal pollution, has become an increasingly serious problem in global agriculture. Anthocyanins, an important plant pigment, are synthesized through the phenylpropanoid pathway and have a variety of physiological and ecological functions, providing multifunctional and effective protection for plants under stress. Foliar anthocyanin accumulation often occurs under abiotic stress including high light, cold, drought, salinity, nutrient deficiency and heavy metal stress, causing leaf reddening or purpling in many plant species. Anthocyanins are used as sunscreens and antioxidants to scavenge reactive oxygen species (ROS), as metal(loid) chelators to mitigate heavy metal stress, and as crucial molecules with a role in delaying leaf senescence. In addition to environmental factors, anthocyanin synthesis is affected by various endogenous factors. Plant hormones such as abscisic acid, jasmonic acid, ethylene and gibberellin have been shown to be involved in regulating anthocyanin synthesis either positively or negatively. Particularly when plants are under abiotic stress, several plant hormones can induce foliar anthocyanin synthesis to enhance plant stress resistance. In this review, we revisit the role of plant hormones in anthocyanin biosynthesis and the mechanism of plant hormone-mediated anthocyanin accumulation and abiotic stress tolerance. We conclude that enhancing anthocyanin content with plant hormones could be a prospective management strategy for improving plant stress resistance, but extensive further research is essentially needed to provide future guidance for practical crop production.

An integrated transcriptome and metabolome analysis reveals the gene network regulating flower development in Pogostemon cablin

Pogostemon cablin is a well-known protected species widely used in medicine and spices, however the underlying molecular mechanisms and metabolite dynamics of P. cablin flower development remain unclear due to the difficulty in achieving flowering in this species. A comparison of the transcriptome and widely targeted metabolome during P. cablin flower development was first performed in this study. Results showed that a total of 13,469 differentially expressed unigenes (DEGs) and 371 differentially accumulated metabolites (DAMs) were identified. Transcriptomic analysis revealed that the DEGs were associated with starch and sucrose metabolism, terpenoid biosynthesis and phenylpropanoid biosynthesis. Among these DEGs, 75 MIKC-MADS unigenes were associated with the development of floral organs. Gibberellins (GAs), auxin, and aging signaling might form a cross-regulatory network to regulate flower development in P. cablin. According to the metabolic profile, the predominant DAMs were amino acids, flavonoids, terpenes, phenols, and their derivatives. The accumulation patterns of these predominant DAMs were closely associated with the flower developmental stage. The integration analysis of DEGs and DAMs indicated that phenylpropanoids, flavonoids, and amino acids might be accumulated due to the activation of starch and sucrose metabolism. Our results provide some important insights for elucidating the reproductive process, floral organ, and color formation of P. cablin flowers at the molecular level. These results will improve our understanding of the molecular and genetic mechanisms involved in the floral development of P. cablin.

Revealing the Roles of the JAZ Family in Defense Signaling and the Agarwood Formation Process in Aquilaria sinensis

Jasmonate ZIM-domain family proteins (JAZs) are repressors in the signaling cascades triggered by jasmonates (JAs). It has been proposed that JAs play essential roles in the sesquiterpene induction and agarwood formation processes in Aquilaria sinensis. However, the specific roles of JAZs in A. sinensis remain elusive. This study employed various methods, including phylogenetic analysis, real-time quantitative PCR, transcriptomic sequencing, yeast two-hybrid assay, and pull-down assay, to characterize A. sinensis JAZ family members and explore their correlations with WRKY transcription factors. The bioinformatic analysis revealed twelve putative AsJAZ proteins in five groups and sixty-four putative AsWRKY transcription factors in three groups. The AsJAZ and AsWRKY genes exhibited various tissue-specific or hormone-induced expression patterns. Some AsJAZ and AsWRKY genes were highly expressed in agarwood or significantly induced by methyl jasmonate in suspension cells. Potential relationships were proposed between AsJAZ4 and several AsWRKY transcription factors. The interaction between AsJAZ4 and AsWRKY75n was confirmed by yeast two-hybrid and pull-down assays. This study characterized the JAZ family members in A. sinensis and proposed a model of the function of the AsJAZ4/WRKY75n complex. This will advance our understanding of the roles of the AsJAZ proteins and their regulatory pathways.

PHOSPHATE STARVATION RESPONSE1 (PHR1) interacts with JASMONATE ZIM-DOMAIN (JAZ) and MYC2 to modulate phosphate deficiency-induced jasmonate signaling in Arabidopsis

Phosphorus (P) is a macronutrient necessary for plant growth and development. Inorganic phosphate (Pi) deficiency modulates the signaling pathway of the phytohormone jasmonate in Arabidopsis thaliana, but the underlying molecular mechanism currently remains elusive. Here, we confirmed that jasmonate signaling was enhanced under low Pi conditions, and the CORONATINE INSENSITIVE1 (COI1)-mediated pathway is critical for this process. A mechanistic investigation revealed that several JASMONATE ZIM-DOMAIN (JAZ) repressors physically interacted with the Pi signaling-related core transcription factors PHOSPHATE STARVATION RESPONSE1 (PHR1), PHR1-LIKE2 (PHL2), and PHL3. Phenotypic analyses showed that PHR1 and its homologs positively regulated jasmonate-induced anthocyanin accumulation and root growth inhibition. PHR1 stimulated the expression of several jasmonate-responsive genes, whereas JAZ proteins interfered with its transcriptional function. Furthermore, PHR1 physically associated with the basic helix-loop-helix (bHLH) transcription factors MYC2, MYC3, and MYC4. Genetic analyses and biochemical assays indicated that PHR1 and MYC2 synergistically increased the transcription of downstream jasmonate-responsive genes and enhanced the responses to jasmonate. Collectively, our study reveals the crucial regulatory roles of PHR1 in modulating jasmonate responses and provides a mechanistic understanding of how PHR1 functions together with JAZ and MYC2 to maintain the appropriate level of jasmonate signaling under conditions of Pi deficiency.