Regulation of Jasmonate-Mediated Stamen Development and Seed Production by a bHLH-MYB Complex in Arabidopsis

ICE1 (Inducer of CBF Expression 1) Is Essential for the Jasmonate-Regulated Development of Stamen in Arabidopsis thaliana

Floral organ development, pollen germination and pollen tube growth are crucial for plant sexual reproduction. Phytohormones maintain these processes by regulating the expression and activity of various transcription factors. ICE1, a MYC-like bHLH transcription factor, has been revealed to be involved in cold acclimatisation of Arabidopsis. This study shows that ICE1 regulates multiple aspects of sexual reproduction, including stamen development, pollen development and germination. Loss-of-function mutants of ICE1 exhibit floral organs with shorter filaments, defective anther dehiscence and lower pollen viability compared to the wild type. These abnormalities result in disrupted fertilisation, leading to short siliques, a high rate of seed abortion, and dark, shriveled mature seeds. JAZ proteins (JAZ1 and JAZ9) interact with ICE1, inhibiting its transcriptional activity on jasmonic acid (JA)-responsive genes, including MYB21, MYB24 and MYB108. This study highlights the essential role of ICE1 as a signalling agent in the JA-regulated maintenance of sexual reproduction in Arabidopsis thaliana.

Genome-wide analysis of KCS genes in tomato and functional characterization of SlKCS8 and SlKCS10 in drought tolerance

KCS, an endogenous cellular enzyme, catalyzes the elongation of fatty acid chains and plays a crucial role in the biosynthesis of plant epidermal wax. Through processes such as transfer, decarboxylation, and fixation, it contributes to plant growth and adaptation to abiotic and biotic stresses. However, the mechanism by which KCS genes participate in the response of tomato plants to driught remains unclear. In this study, 15 SlKCS gene family members were identified in tomato using bioinformatics methods. Comprehensive analyses were conducted on their amino acid sequences, conserved motifs, cis-elements, phylogenetic relationships, duplication events, and collinearity. Transcriptome and qRT-PCR analysis revealed diverse expression patterns of SlKCS genes under abiotic stresses, with SlKCS8 and SlKCS10 displaying significant upregulation during drought conditions. The two genes were localized to the plasma membrane and exhibit tissue-specific expression. Functional studies demonstrated that silencing SlKCS8 and SlKCS10 reduced drought tolerance in tomato by disrupting stomatal closure. Further analysis revealed that the silencing of KCS compromised the drought tolerance of tomato by reducing its capacity to scavenge reactive oxygen species. These findings provide critical insights into the regulatory functions of SlKCS genes, particularly SlKCS8 and SlKCS10, in drought resistance. Additionally, this research offers important genetic resources for developing drought-tolerant tomato cultivars.

Research Advances and Perspectives on Early Flowering Traits in Cucumber

Early flowering refers to the phenomenon in which the first flower appears in fewer days than normal, regardless of the sex of the flower. It is a significant feature impacting the early maturity and economic yield of cucumbers. The early flowering trait of cucumber is influenced by several factors. Considering its heritability, technologies such as whole-genome sequencing, genetic modification, bioinformatics analysis, quantitative trait locus (QTL) mapping, molecular marker-assisted selection, and gene editing are widely used to explore the regulatory genes and molecular mechanisms of the early flowering trait in cucumbers. This review aimed to summarize the factors, QTL mapping, molecular regulation mechanisms, and omics analysis related to early flowering traits in cucumbers. This review contributes theoretical insights to support both cucumber breeding for early flowering and fundamental research on early flowering traits.

The LoMYB26/LoJAZ4-LoCOMT module regulates anther dehiscence via Jasmonic acid-mediated endothecium lignification in lily

INTRODUCTION

Timely anther dehiscence is a key step for successful sexual reproduction in plants. Secondary cell wall thickening of anther endothecium is a vital process during anther dehiscence that provides an indispensable mechanical force for successful dehiscence. Anther dehiscence depends on anther lignification, and it is a timely and sophisticated process regulated by phytohormones and transcription factors. However, whether endothecium lignification occurs during anther dehiscence in lily and underlying mechanisms are still largely unclear.

OBJECTIVES

Our work focuses on identifying the course of endothecium lignification during anther dehiscence and elucidating the molecular mechanisms underlying endothecium lignification-dependent anther dehiscence in lily.

METHODS

Lignin fluorescence analysis and ultraviolet spectrophotometry were employed to elucidate the endothecium lignification process. Target genes were isolated from the transcriptomic data of anther dehiscence and lignification process. Virus-induced gene silencing (VIGS) and transient overexpression in lily anthers were used to analyze the LoMYB26 function. Yeast one-hybrid (Y1H), electrophoretic mobility shift assay (EMSA), and dual-luciferase (LUC) assay analyzed the regulatory mechanisms. Yeast two-hybrid (Y2H), luciferase complementation imaging (LCI), and bimolecular fluorescence complementation (BiFC) assays illustrated the interaction between LoMYB26 and LoJAZ4.

RESULTS

Our results showed that endothecium lignification occurred in S6-S7 stages when anther dehiscence had not yet occurred. The R2R3-type MYB transcription factor, LoMYB26, was found to promote endothecium lignification. LoMYB26 directly bound to the Caffeic Acid O-methyltransferase (LoCOMT) promoter and activated its transcription. Meanwhile, LoMYB26 interacted with jasmonate-ZIM domain protein 4 (LoJAZ4), which repressed the LoMYB26-mediated activation of LoCOMT transcription. Additionally, the exogenous application of methyl-jasmonate (Me-JA) induced LoMYB26 transcription and promoted endothecium lignification.

CONCLUSION

Our findings demonstrate that LoMYB26 promotes endothecium lignification and anther dehiscence. LoMYB26 interacted with LoJAZ4, forming a heterodimer that participates in JA-mediated endothecium lignification and anther dehiscence. This study offers valuable insights and a theoretical foundation for the breeding of anther-indehiscent lily.

Transcriptomic analysis of regulating the growth and development of tomato seedlings by the crosstalk between JA and TOR signaling

KEY MESSAGE

Transcription factors MYB, WRKY, bHLH, bZIP and NAC were identified as key candidate genes for JA and TOR regulation of tomato seedling growth and development. Jasmonic acid (JA) and Target of Rapamycin (TOR) signaling pathways interact to regulate plant growth, development, and stress responses. In this study, transcriptomic and weighted gene co-expression network analysis (WGCNA) were conducted on tomato wild-type (WT) and spr2 mutant lines treated with the TOR inhibitor RAP and activator MHY1485. We identified key roles of MAPK kinase and ethylene signaling in mediating JA-TOR interaction. Core transcription factors, including MYB, WRKY, bHLH, bZIP, and NAC, were highlighted as central regulators within the interaction between JA and TOR signaling network. These findings advance our understanding of how JA and TOR signaling coordinate plant growth and stress adaptation.

Identification of Nuclear Localization Sequence (NLS) Sites in R2R3-MYB Transcription Factor Involved in Anther Development

The R2R3-MYB family of transcription factors (TFs) plays a crucial role in cell specification and secondary metabolism regulation during plant development. In Arabidopsis, MS188, a typical R2R3-MYB protein, is essential for tapetal development and pollen wall formation. However, the nuclear localization sequence (NLS) responsible for directing MS188 into the nucleus has not been fully elucidated. In this study, the subcellular localization of the NLS-containing proteins was determined by GFP tagging in tobacco leaves, and three NLS regions within MS188 were identified: two located at the N-terminus of R2-MYB and one at the C-terminus of R3-MYB. We further narrowed the NLSs located at amino acids (AAs) 12-15, 18-22, and 96-107 via point mutation analysis. Combined with the cytoplasmic protein FBA6, these NLSs fusion proteins could localize in the nucleus. Importantly, the proteins with mutations in AAs 18-22 exhibited completely cytoplasmic signals, whereas other mutated sites partially abolished the nuclear signals. These findings suggest that the NLS at AAs 18-22 is sufficient for nuclear localization. To confirm the NLS functions in vivo, we constructed the vectors including the MS188 gene without the NLS sites, which failed to complement the male sterile phenotype of ms188. We also searched the highly conserved NLSs in other R2R3-MYB TFs and showed they are required for nuclear localization. Collectively, these findings revealed the specific NLS regions within R2R3-MYB transcription factors and highlighted their critical role for subcellular localization in plant developmental regulation.

Transcriptome and Metabolome Profiling Provide Insights into Flavonoid Biosynthesis and the Mechanism of Color Formation in Zanthoxylum bungeanum Maxim

The color of Zanthoxylum bungeanum Maxim. (Z. bungeanum) is a key quality indicator and a factor limiting the development of its industry. However, the underlying mechanisms governing color formation remain largely unexplored. In this study, an integrative analysis of transcriptome and metabolome profiles was conducted across four developmental stages to elucidate the color formation mechanism in Z. bungeanum. A total of 137 flavonoids were identified as the fruits ripened, with high levels of differentially accumulated metabolites (DAMs), including tricetin and (-)-epigallocatechin, which were strongly associated with color formation. This suggests their significant contribution to the pigmentation process. Nine differentially expressed genes (DEGs) were identified as candidate genes involved in color development. Additionally, 15 transcription factors (TFs) (12 MYB and 3 bHLH) exhibited expression patterns similar to those of structural genes in the flavonoid biosynthetic pathway, indicating their role in regulating flavonoid synthesis. The bioinformatics analysis of three key flavonoid synthesis genes-ZbCHI, ZbFLS, and ZbANR-revealed that all three proteins exhibit hydrophobic structures without transmembrane domains. Among them, ZbANR possesses signal peptide regions, whereas ZbCHI and ZbFLS do not. Subcellular localization predictions suggest that ZbCHI is most likely localized in the chloroplast, ZbFLS in the cytoplasm, and ZbANR in the membrane. Functional analyses revealed that their transient expression in Nicotiana benthamiana (N. benthamiana) increased the flavonoid content, with ZbANR overexpression producing a distinct white phenotype in the plants. This study enriches transcriptomic data and provides a comprehensive understanding of flavonoid metabolism and the molecular basis of color formation in Z. bungeanum, offering a valuable theoretical foundation for future breeding programs.

The concerted function of a novel class of transcription factors, ZBFs, in light, jasmonate, and abscisic acid signaling pathways

Several classes of transcription factors have been investigated in light signaling pathways that bind to the light-responsive elements (LREs) present in the promoters of light regulatory genes for transcriptional regulation. Some of these transcription factors have been shown to bind to numerous promoters through genome-wide ChIP-on-chip (ChIP-chip) studies. Furthermore, through the integration of ChIP-seq and RNA-seq techniques, it has been demonstrated that a transcription factor modifies the expression of numerous genes with which it interacts. However, the mode of action of these transcription factors and their dependency on other regulators in the pathway has just started to be unraveled. In this review, we focus on a particular class of transcription factors, ZBFs (Z-box-binding factors), and their associated partners within the same or other classes of transcription factors and regulatory proteins during photomorphogenesis. Moreover, we have further made an attempt to summarize the crosstalk of these transcription factors with jasmonic acid-, abscisic acid-, and salicylic acid-mediated defense signaling pathways. This review offers an in-depth insight into the manner in which ZBFs and their interactors reshape cellular functions and plant behavior. The underlying principles not only contribute to a comprehensive understanding but also establish a framework for analyzing the interplay between early developmental events and hormone signaling, a regulation orchestrated by the ZBF family.

Genome-wide identification of the bHLH gene family and the mechanism regulation of anthocyanin biosynthesis by ChEGL1 in Cerasus humilis

Cerasus humilis is a fruit tree with enormous potential economic value, and its fruit is rich in various bioactive substances. The basic helix loop helix (bHLH) gene family plays an important role in the biosynthesis of plant anthocyanins. However, there was no research on the ChbHLH gene family in C. humilis. In this study, 114 ChbHLH genes were identified from the C. humilis genome and divided into 17 subgroups. Then, evolutionary relationships, conserved motifs, gene structures, and cis-acting elements were analyzed. By predicting the interaction network between ChbHLH proteins and ChMYB1, it was found that ChbHLH44 (here named as ChEGL1) was located at the core of the interaction network. Further experiments revealed that ChEGL1 and ChMYB1 could interact with each other both in vivo and in vitro. In addition, ChEGL1 significantly increased the anthocyanin content in transgenic tomato plants. This study provides a comprehensive understanding of the ChbHLH gene family and supports further enrichment of the regulation mechanism of anthocyanin biosynthesis in C. humilis fruit.

The AMS/DYT1-MYB module interacts with the MED25-MYC-MYB complexes to inhibit jasmonate-regulated floral defense in Arabidopsis

The phytohormone jasmonates (JAs) regulate plant growth and defense responses. The reproductive organs of flowers are devastated by insect herbivores. However, the molecular mechanisms of floral defense remain largely unknown. Here, we found that the Arabidopsis JA receptor CORONATINE INSENSITIVE1 (COI1) and its substrates JA ZIM-domain (JAZ) repressors, and the mediator subunit MEDIATOR25-based MED25-MYC-MYB (MMM) complexes, including MYC2/3/4/5 and MYB28/29/76, mediated floral defense against the insects Helicoverpa armigera, Spodoptera exigua, and Spodoptera frugiperda. The flower-specific IIIa bHLH factors ABORTED MICROSPORES (AMS) and DYSFUNCTIONAL TAPETUM 1 (DYT1) were JAZ-interaction proteins. They interacted with members of the MMM complexes, inhibited the transcriptional activity of MYC2 and MYB28, and repressed floral defense against insects. AMS and DYT1 recruited the flower-specific MYB21/24, and these MYBs interacted with members of MMM complexes, inhibited the MYC2-MYB28 function, and suppressed floral defense against insects. Our study revealed that the JA-COI1-JAZ-MMM pathway mediated flower defense, and the AMS/DYT1-MYB21/24 module antagonized the MMM complexes to repress floral defense against insects.

ERF114/115/109 are essential for jasmonate-repressed non-canonical JAZ8 activity in JA signaling

Jasmonate (JA), a key plant hormone, regulates various aspects of plant development and stress responses, primarily through the degradation of canonical jasmonate-ZIM domain (JAZ) proteins by the SCFCOI1 complex. While JAZ8, a non-canonical JAZ protein lacking the degron signal, has been shown to repress JA responses, the mechanism by which JA inhibits JAZ8 activity remains unclear. Here, we demonstrate that Arabidopsis ethylene response factor 114 (ERF114), ERF115, and ERF109 regulate JA signaling through interacting with JAZ8. This interaction disrupts the formation of the MYC2/3/4-JAZ8 and root hair defective 6 (RHD6)-JAZ8 complexes. We show that ERF114 positively regulates JA-induced transcriptional responses and that JA-promoted root hair growth is highly alleviated in erf114 mutants. Furthermore, the transcription of ERF114/115/109 is induced by JA in an MYC2-dependent manner, thus forming a positive feedback loop in JA signaling. Collectively, this study reveals a regulatory pathway in which ERF114/115/109 regulate JA signaling by targeting non-canonical JAZ proteins.

MsMYB206-MsMYB450-MsHY5 complex regulates alfalfa tolerance to salt stress via regulating flavonoid biosynthesis during the day and night cycles

Flavonoids are the major secondary metabolites participating in many biological processes of plants. Although flavonoid biosynthesis has been extensively studied, its regulatory mechanisms during the day and night cycles remain poorly understood. In this study, three proteins, MsMYB206, MsMYB450, and MsHY5, were found to interact with each other, in which MsMYB206 directly transactivated two flavonoid biosynthetic genes, MsFLS and MsF3'H. The expression patterns of MsMYB206, MsMYB450, MsFLS, and MsF3'H were fully consistent at regular intervals across day/night cycles that were higher at night than in the daytime. On the contrary, both gene expression levels and protein contents of MsHY5 increased in the daytime but decreased at night, and the lower expression of MsHY5 at night led to strengthened interaction between MsMYB206 and MsMYB450. The MsMYB206-overexpression plants were more salt-tolerant and their flavonoid contents were higher than the WT during the day/night cycles. This study revealed one mechanism interpreting the fluctuating flavonoid contents during day/night cycles regulated by the MsMYB206/MsMYB450/MsHY5-MsFLS/MsF3'H module that also contributed to salt tolerance in alfalfa.

EMBRYONIC FLOWER 1 regulates male reproduction by repressing the jasmonate pathway downstream transcription factor MYB26

The evolutionarily conserved Polycomb repressive complexes (PRCs) mediate genome-wide transcriptional silencing and regulate a plethora of development, as well as environmental responses in multicellular organisms. The PRC2-catalyzed trimethylation of lysine 27 on histone H3 (H3K27me3) is recognized by reader-effector modules of Polycomb repressive complex 1 (PRC1) to implement gene repression. Here, we report that the Arabidopsis (Arabidopsis thaliana) H3K27me3 effector EMBRYONIC FLOWER 1 (EMF1) interacts with and constrains the R2R3 DNA binding transcription factor MYB26 by a eudicot-conserved motif in the stamen. MYB26 activates the transcription of two NAC domain genes, NAC SECONDARY WALL THICKENING PROMOTING FACTOR1 (NST1) and NST2, whose encoded proteins mediate anther secondary cell thickening in jasmonate (JA)-regulated stamen maturation. In this process, the transcriptional activity of MYB26 is negatively modulated by the JAZ-PRC repressive complex to precisely regulate the expression of NST1 and NST2. Disruption of EMF1 repression stimulates MYB26, leading to the excessive transcription of the two NAC genes and male sterility. Our results reveal a novel mechanism in Polycomb-mediated gene silencing and illustrate that the plant Polycomb complex regulates stamen development by preventing the hypersensitivity of JA responses in male reproduction.

Jasmonate induces translation of the Arabidopsis transfer RNA-binding protein YUELAO1, which activates MYC2 in jasmonate signaling

Jasmonate is ubiquitous in the plant kingdom and regulates multiple physiological processes. Although jasmonate signaling has been thoroughly investigated in Arabidopsis thaliana, most studies have focused on the transcriptional mechanisms underlying various jasmonate responses. It remains unclear whether (and how) translation-related pathways help improve transcription efficiency to modulate jasmonate signaling, which may enable plants to respond to stressful conditions effectively. Here, we demonstrate that jasmonate induces translation of the transfer RNA (tRNA)-binding protein YUELAO 1 (YL1) via a specific region in its 3' untranslated region (3' UTR). YL1 and its homolog YL2 redundantly stimulate jasmonate responses such as anthocyanin accumulation and root growth inhibition, with the YL1 3' UTR being critical for YL1-promoted jasmonate responses. Once translated, YL1 acts as an activator of the MYC2 transcription factor through direct interaction, and disrupting YL1 3' UTR impairs the YL1-mediated transcriptional activation of MYC2. YL1 enhances jasmonate responses mainly in a MYC2-dependent manner. Together, these findings reveal a translational mechanism involved in jasmonate signaling and advance our understanding of the transcriptional regulation of jasmonate signaling. The YL1 3' UTR acts as a crucial signal transducer that integrates translational and transcriptional regulation, allowing plants to respond to jasmonate in a timely fashion.

Transcriptomics and metabolomics analyses reveal pollen abortion mechanism in alfalfa early stage male sterile lines

Alfalfa (Medicago sativa L.), a prominent perennial forage in the legume family, is widely cultivated across Europe and America. Given its substantial economic value for livestock, breeding efforts have focused on developing high-yield and high-quality varieties since the discovery of CMS lines. However, progress is restricted by the limitations of existing CMS lines, necessitating the development of new lines and study of the molecular mechanisms underlying pollen abortion. This study investigates early-stage anther development in cytoplasmic male sterile (CMS) alfalfa lines (MSJN1A) in relation to the isotypic maintainer line (MSJN1B). Histological analyses revealed abnormal degradation of tapetal cells post-meiosis in the CMS line. Notably, during the early mononuclear stage, the central vacuoles in the microspores were absent, leading to evident pollen abortion. These findings suggest that pollen abortion in the CMS line is associated with the delayed disintegration of the tapetum and structural anomalies in microspore vacuoles. Non-targeted metabolome sequencing revealed 401 and 405 metabolites at late tetrad and early mononuclear stages of alfalfa, respectively. Among these, 39 metabolites were consistently upregulated, whereas 85 metabolites were downregulated. Differential analysis revealed 45 and 37 unique metabolites at each respective stage. These metabolites were primarily featured in pathways related to energy, phenylpropane, sucrose and starch, and fatty acid metabolism. Integrated analysis demonstrated that differentially expressed genes and differential metabolites were co-enriched in these pathways. Additionally, quantitative real-time PCR and physiological index analysis confirmed downregulation of key genes involved in anther development, illustrating that changes in upstream gene regulation could significantly impact downstream metabolite levels, ultimately influencing pollen fertility. Pollen abortion is related to abnormal phenylpropane metabolism, fatty acid metabolism and starch and sucrose pathway, which provides reference for further research on the causes of pollen abortion of alfalfa.

bHLH19 and bHLH20 repress jasmonate-mediated plant defense against insect herbivores in Arabidopsis

Plants are attacked by various insect herbivores. Upon attack-triggered biosynthesis of the phytohormone jasmonates (JAs), the JA receptor CORONATINE INSENSITIVE 1 recruits the JA-ZIM domain (JAZ) repressors for ubiquitination, releases the MYC-MYB transcription factor (TF) complexes, and enhances glucosinolates (GSs) biosynthesis to promote defense against insects in Arabidopsis. However, the negative regulation of JA-regulated defense remains largely unclear. Here, we found that Arabidopsis IVa bHLH TFs bHLH19 and bHLH20 interacted with JAZs. The bhlh19/20 mutations enhanced defense against the insects Spodoptera frugiperda and S. exigua, while their overexpression inhibited defense. bHLH19/20 repressed defense via at least two layers of regulation: first, bHLH19/20 interacted with the members MYC2/3/4/5 and MYB34/51/122 of MYC-MYB complexes, and inhibited the interaction/transcription activity of MYC2-MYB34; second, bHLH19/20 activated the RNA level of nitrile-specifier protein 1, which converts GSs into the less toxic nitriles. bhlh19/20 exhibited no penalty in JA-regulated growth inhibition. Collectively, our findings reveal the molecular mechanism for negatively regulating JA-mediated defense against insects in Arabidopsis without growth penalty by the pair of bHLH19/20 TFs.

The MYC2 and MYB43 transcription factors cooperate to repress HMA2 and HMA4 expression, altering cadmium tolerance in Arabidopsis thaliana

Cadmium (Cd) represents a hazardous heavy metal, prevalent in agricultural soil due to industrial and agricultural expansion. Its propensity for being absorbed by edible plants, even at minimal concentrations, and subsequently transferred along the food chain poses significant risks to human health. Accordingly, it is imperative to investigate novel genes and mechanisms that govern Cd tolerance and detoxification in plants. Here, we discovered that the transcription factor MYC2 directly binds to the promoters of HMA2 and HMA4 to repress their expression, thereby altering the distribution of Cd in plant tissues and negatively regulating Cd stress tolerance. Additionally, molecular, biochemical, and genetic analyses revealed that MYC2 interacts and cooperates with MYB43 to negatively regulate the expression of HMA2 and HMA4 and Cd stress tolerance. Notably, under Cd stress conditions, MYC2 undergoes degradation, thereby alleviating its inhibitory effect on HMA2 and HMA4 expression and plant tolerance to Cd stress. Thus, our study highlights the dynamic regulatory role of MYC2, in concert with MYB43, in regulating the expression of HMA2 and HMA4 under both normal and Cd stress conditions. These findings present MYC2 as a promising target for directed breeding efforts aimed at mitigating Cd accumulation in edible plant roots.

Genome-Wide Profiling of the ACTIN Gene Family and Its Implications for Agronomic Traits in Brassica napus: A Bioinformatics Study

ACTINs are key structural proteins in plants, which form the actin cytoskeleton and are engaged in numerous routine cellular processes. Meanwhile, ACTIN, recognized as a housekeeping gene, has not yet been thoroughly investigated in Brassica napus. The current research has led to the detection of 69 actin genes in B. napus, which were organized into six distinct subfamilies on the basis of phylogenetic relationships. Functional enrichment analysis, along with the construction of protein interaction networks, suggested that BnACTINs play roles in Preserving cell morphology and facilitating cytoplasmic movement, plant development, and adaptive responses to environmental stress. Moreover, the BnACTIN genes presented a wide range of expression levels among different tissues, whereas the majority experienced a substantial increase in expression when subjected to various abiotic stresses, demonstrating a pronounced sensitivity to abiotic factors. Furthermore, association mapping analysis indicated that some BnACTINs potentially affected certain key agronomic traits. Overall, our research deepens the knowledge of BnACTIN genes, promotes the cultivation of improved B. napus strains, and lays the groundwork for subsequent functional research.

The Arabidopsis ARID-HMG DNA-BINDING PROTEIN 15 modulates jasmonic acid signaling by regulating MYC2 during pollen development

The intricate process of male gametophyte development in flowering plants is regulated by jasmonic acid (JA) signaling. JA signaling initiates with the activation of the basic helix-loop-helix transcription factor (TF), MYC2, leading to the expression of numerous JA-responsive genes during stamen development and pollen maturation. However, the regulation of JA signaling during different stages of male gametophyte development remains less understood. This study focuses on the characterization of the plant ARID-HMG DNA-BINDING PROTEIN 15 (AtHMGB15) and its role in pollen development in Arabidopsis (Arabidopsis thaliana). Phenotypic characterization of a T-DNA insertion line (athmgb15-4) revealed delayed bolting, shorter siliques, and reduced seed set in mutant plants compared to the wild type. Additionally, AtHMGB15 deletion resulted in defective pollen morphology, delayed pollen germination, aberrant pollen tube growth, and a higher percentage of nonviable pollen grains. Molecular analysis indicated the downregulation of JA biosynthesis and signaling genes in the athmgb15-4 mutant. Quantitative analysis demonstrated that JA and its derivatives were ∼10-fold lower in athmgb15-4 flowers. Exogenous application of methyl jasmonate could restore pollen morphology and germination, suggesting that the low JA content in athmgb15-4 impaired JA signaling during pollen development. Furthermore, our study revealed that AtHMGB15 physically interacts with MYC2 to form a transcription activation complex. This complex promotes the transcription of key JA signaling genes, the R2R3-MYB TFs MYB21 and MYB24, during stamen and pollen development. Collectively, our findings highlight the role of AtHMGB15 as a positive regulator of the JA pathway, controlling the spatiotemporal expression of key regulators involved in Arabidopsis stamen and pollen development.

Genome-Wide Identification, Phylogenetic, and Expression Analysis of Jasmonate ZIM-Domain Gene Family in Medicago Sativa L

JASMONATE ZIM domain (JAZ) proteins, inhibitors of the jasmonic acid (JA) signaling pathway, are identified in different plants, such as rice and Arabidopsis. These proteins are crucial for growth, development, and abiotic stress responses. However, limited information is available regarding the JAZ family in alfalfa. This study identified 11 JAZ genes (MsJAZs) in the "Zhongmu No.1" reference genome of alfalfa. The physical and chemical properties, chromosome localization, phylogenetic relationships, gene structure, cis-acting elements, and collinearity of the 11 MsJAZ genes were subsequently analyzed. Tissue-specific analysis revealed distinct functions of different MsJAZ genes in growth and development. The expression patterns of MsJAZ genes under salt stress conditions were validated using qRT-PCR. All MsJAZ genes responded to salt stress, with varying levels of upregulation over time, highlighting their role in stress responses. Furthermore, heterogeneous expression of MsJAZ1 in Arabidopsis resulted in significantly lower seed germination and survival rates in OE-2 and OE-4 compared to the WT under 150 mM NaCl treatment. This study establishes a foundation for further exploration of the function of the JAZ family and provides significant insights into the genetic improvement of alfalfa.

Identification of MYC genes in four Cucurbitaceae species and their roles in the response to temperature stress

BACKGROUND

Myelocytomatosis (MYC) transcription factors are crucial mediators of the response of plants to environmental stresses through via binding to DNA regulatory regions. However, few systematic characterizations of MYC genes are available in Cucurbitaceae species.

RESULTS

In this study, we identified 10, 8, 12, and 10 MYC genes in Cucumis sativus, Cucumis melo, Citrullus lanatus, and Benincasa hispida, respectively. Characterization revealed that all of the MYC proteins contain a highly conserved H4-V5-E6-E8-R9-R11-R12 sequence, which is essential for the binding of DNA regulatory regions. Evolutionary analysis enabled us to categorize 40 predicted MYC proteins from seven species into five distinct groups and revealed that the expansion of the MYC genes occurred before the divergence of monocots and dicots. The upstream promoter regions of the MYC genes contain a variety of developmental, stress, and hormone-responsive regulatory elements. The expression of cucumber MYC genes varies significantly across organs, with particularly high expression of CsaV3_3G001710 observed across all organs. Transcriptomic analysis revealed that certain cucumber MYC genes undergo specific upregulation or downregulation in response to both biotic and abiotic stressors. In particular, under temperature stress, the cucumber genes CsaV3_3G007980 and CsaV3_3G001710 were significantly upregulated. Interestingly, the homologs of these two genes in C. lanatus presented a similar expression pattern to that in C. sativus, whereas in B. hispida, they presented the opposite pattern, i.e., significant downregulation. These findings indicated that these two genes indeed respond to temperature stress but with different expression patterns, highlighting the divergent functions of homologous genes across different species.

CONCLUSIONS

This study analyzed the size and composition of the MYC gene family in four Cucurbitaceae species and investigated stress-responsive expression profiles, especially under temperature stress. All the results showed that MYC genes play important roles in development and stress responses, laying a theoretical foundation for further investigations of these response mechanisms.

Dynamic temporal transcriptome analysis reveals grape VlMYB59-VlCKX4 regulatory module controls fruit set

Fruit set is a key stage in determining yield potential and guaranteeing quality formation and regulation. N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) has been widely applied in grape production, the most iconic of which is the promotion of grape fruit set. However, current studies still lack the molecular mechanism of CPPU-induced grape fruit set. Here, the dynamic, high-resolution stage-specific transcriptome profiles were generated based on two different treatments and five developmental periods during fruit set in 'Kyoho' grape (Vitis vinifera L. × V. labrusca L.). Pairwise comparison and functional category analysis showed that phytohormone action cytokinin was significantly enriched during the CPPU-induced grape fruit set, but not the natural one. Value differentially expressed gene (VDEG) was a newly proposed analysis strategy for mining genes related to the grape fruit set. Notably, the cytokinin metabolic process was significantly enriched among up-regulated VDEGs. Of importance, a key VDEG VlCKX4 related to the cytokinin metabolic process was identified as related to the grape fruit set. Overexpression of VlCKX4 gene promoted the Arabidopsis plants that produce more and heavier siliques. The transcription factor VlMYB59 directly bound to the promoter of VlCKX4 and activated its expression. Moreover, overexpression of VlMYB59 gene also promoted the Arabidopsis fruit set. Overall, VlMYB59 responded to CPPU treatment and directly activated the expression of VlCKX4, thus promoting the fruit set. A regulatory pathway of the VlMYB59-VlCKX4 module in the fruit set was uncovered, which provides important insights into the molecular mechanisms of the fruit set and good genetic resources for high fruit set rate breeding.

Overexpression of a 'Paulownia fortunei' MYB Factor Gene, PfMYB44, Increases Salt and Drought Tolerance in Arabidopsis thaliana

Paulownia fortunei (Seem.) Hemsl is a Paulownia Sieb.et tree of the family Scrophulariaceae. It has become an important short-to-medium-term fast-growing multi-purpose tree species in China due to its rapid growth, strong adaptability, and excellent material properties. MYB transcription factors in plants have numerous and diverse functions, playing important roles in various aspects such as plant stress response. To investigate the function of MYB transcription factors in Paulownia fortunei, this study used PCR technology to clone the PfMYB44 gene from Paulownia fortunei. The homology of PfMYB44 and SiMYB44 (Sesamum indicum) was the highest. Expression analysis results showed that PfMYB44 was expressed in the root, stem, young leaf, and mature leaf of Paulownia fortunei, with the highest content in the root. Cold, drought, hot, salt, and ABA treatments could increase the expression level of PfMYB44. Overexpression-PfMYB44 plants were constructed, and physiological and molecular analysis showed that PfMYB44 could positively regulate salt and drought stresses. Under drought stress, the expression levels of AtP5CS, AtCAT1, AtNCED3 and AtSnRK2.4 in transgenic lines were significantly induced. Salt stress induced the expression of AtNHX1, AtSOS1, AtSOS2 and AtSOS3 genes, and the relative expression levels of these genes in transgenic Arabidopsis were higher. In conclusion, the functional study of PfMYB44 laid a certain foundation for the study of Paulownia stress resistance, and was helpful to the study of its stress resistance mechanism and the cultivation of new stress resistance varieties.

The jasmonate pathway promotes nodule symbiosis and suppresses host plant defense in Medicago truncatula

Root nodule symbiosis (RNS) between legumes and rhizobia is a major source of nitrogen in agricultural systems. Effective symbiosis requires precise regulation of plant defense responses. The role of the defense hormone jasmonic acid (JA) in the immune response has been extensively studied. Current research shows that JA can play either a positive or negative regulatory role in RNS depending on its concentration, but the molecular mechanisms remain to be elucidated. In this study, we found that inoculation with the rhizobia Sm1021 induces the JA pathway in Medicago truncatula, and blocking the JA pathway significantly reduces the number of infection threads. Mutations in the MtMYC2 gene, which encodes a JA signaling master transcription factor, significantly inhibited rhizobia infection, terminal differentiation, and symbiotic cell formation. Combining RNA sequencing and chromatin immunoprecipitation sequencing, we discovered that MtMYC2 regulates the expression of nodule-specific MtDNF2, MtNAD1, and MtSymCRK to suppress host defense, while it activates MtDNF1 expression to regulate the maturation of MtNCRs, which in turn promotes bacteroid formation. More importantly, MtMYC2 participates in symbiotic signal transduction by promoting the expression of MtIPD3. Notably, the MtMYC2-MtIPD3 transcriptional regulatory module is specifically present in legumes, and the Mtmyc2 mutants are susceptible to the infection by the pathogen Rhizoctonia solani. Collectively, these findings reveal the molecular mechanisms of how the JA pathway regulates RNS, broadening our understanding of the roles of JA in plant-microbe interactions.

The characteristic analysis of TaTDF1 reveals its function related to male sterility in wheat (Triticum aestivum L.)

BACKGROUND

The male sterile lines are an important foundation for heterosis utilization in wheat (Triticum aestivum L.). Thereinto, pollen development is one of the indispensable processes of wheat reproductive development, and its fertility plays an important role in wheat heterosis utilization, and are usually influencing by genes. However, these key genes and their regulatory networks during pollen abortion are poorly understood in wheat.

RESULTS

DEFECTIVE IN TAPETAL DEVELOPMENT AND FUNCTION 1 (TDF1) is a member of the R2R3-MYB family and has been shown to be essential for early tapetal layer development and pollen grain fertility in rice (Oryza sativa L.) and Arabidopsis thaliana. In order to clarify the function of TDF1 in wheat anthers development, we used OsTDF1 gene as a reference sequence and homologous cloned wheat TaTDF1 gene. TaTDF1 is localized in the nucleus. The average bolting time of Arabidopsis thaliana overexpressed strain (TaTDF1-OE) was 33 d, and its anther could be colored normally by Alexander staining solution, showing red. The dominant Mosaic suppression silence-line (TaTDF1-EAR) was blue-green in color, and the anthers were shrimpy and thin. The TaTDF1 interacting protein (TaMAP65) was confirmed using Yeast Two-Hybrid Assay (Y2H) and Bimolecular-Fluorescence Complementation (BiFC) experiments. The results showed that downregulated expression of TaTDF1 and TaMAP65 could cause anthers to be smaller and shrunken, leading to pollen abortion in TaTDF1 wheat plants induced by virus-induced gene-silencing technology. The expression pattern of TaTDF1 was influenced by TaMAP65.

CONCLUSIONS

Thus, systematically revealing the regulatory mechanism of wheat TaTDF1 during anther and pollen grain development may provide new information on the molecular mechanism of pollen abortion in wheat.

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.

FhMYB108 Regulates the Expression of Linalool Synthase Gene in Freesia hybrida and Arabidopsis

Acting as the most abundant and widely distributed volatile secondary metabolites in plants, terpenoids play crucial roles in diverse physiological regulations and metabolic processes. Terpene synthases play a decisive role in determining the composition and diversity of terpenoids. Though the regulation of terpene synthases has been extensively investigated across various plant species, limited studies have focused on the upstream transcriptional regulation of terpene synthases. In this study, we have identified linalool as the predominant volatile compound that is released gradually from Freesia hybrida flowers throughout flower blooming. In the context of the transcriptome, a typical MYB transcription factor, FhMYB108, was screened based on homologous gene comparison. FhMYB108 is capable of regulating the expression of FhTPS1, and both their expression levels showed gradual increase during flower opening. Moreover, FhMYB108 exerts a stimulatory effect on the transcription of Arabidopsis thaliana AtTPS14, while no significant increase in AtTPS14 expression is observed upon the stabilization of FhMYB108 in A. thaliana. The highly expressed AtMYC2 in A. thaliana could interact with FhMYB108 to suppress the activation of AtTPS14 by FhMYB108. The present study not only elucidates the regulatory mechanism underlying linalool synthesis but also discovers the synergistic effect of MYB and bHLH transcription factors in governing the biosynthesis of volatile terpenoids.

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.

Transcription factor NtNAC56 regulates jasmonic acid-induced leaf senescence in tobacco

Leaf senescence is a vital aspect of plant physiology and stress responses and is induced by endogenous factors and environmental cues. The plant-specific NAC (NAM, ATAF1/2, CUC2) transcription factor family influences growth, development, and stress responses in Arabidopsis (Arabidopsis thaliana) and other species. However, the roles of NACs in tobacco (Nicotiana tabacum) leaf senescence are still unclear. Here, we report that NtNAC56 regulates leaf senescence in tobacco. Transgenic plants overexpressing NtNAC56 (NtNAC56-OE) showed induction of senescence-related genes and exhibited early senescence and lower chlorophyll content compared to wild-type (WT) plants and the Ntnac56-19 mutant. In addition, root development and seed germination were inhibited in the NtNAC56-OE lines. Transmission electron microscopy observations accompanied by physiological and biochemical assays revealed that NtNAC56 overexpression triggers chloroplast degradation and reactive oxygen species accumulation in tobacco leaves. Transcriptome analysis demonstrated that NtNAC56 activates leaf senescence-related genes and jasmonic acid (JA) biosynthesis pathway genes. In addition, the JA content of NtNAC56-OE plants was higher than in WT plants, and JA treatment induced NtNAC56 expression. We performed DNA affinity purification sequencing to identify direct targets of NtNAC56, among which we focused on LIPOXYGENASE 5 (NtLOX5), a key gene in JA biosynthesis. A dual-luciferase reporter assay and a yeast one-hybrid assay confirmed that NtNAC56 directly binds to the TTTCTT motif in the NtLOX5 promoter. Our results reveal a mechanism whereby NtNAC56 regulates JA-induced leaf senescence in tobacco and provide a strategy for genetically manipulating leaf senescence and plant growth.

Transcriptomics analyses reveal the key genes involved in stamen petaloid formation in Alcea rosea L

Alcea rosea L. is a traditional flower with a long cultivation history. It is extensively cultivated in China and is widely planted in green belt parks or used as cut flowers and potted ornamental because of its rich colors and flower shapes. Double-petal A. rosea flowers have a higher aesthetic value compared to single-petal flowers, a phenomenon determined by stamen petaloid. However, the underlying molecular mechanism of this phenomenon is still very unclear. In this study, an RNA-based comparative transcriptomic analysis was performed between the normal petal and stamen petaloid petal of A. rosea. A total of 3,212 differential expressed genes (DEGs), including 2,620 up-regulated DEGs and 592 down-regulated DEGs, were identified from 206,188 unigenes. Numerous DEGs associated with stamen petaloid were identified through GO and KEGG enrichment analysis. Notably, there were 63 DEGs involved in the plant hormone synthesis and signal transduction, including auxin, cytokinin, gibberellin, abscisic acid, ethylene, brassinosteroid, jasmonic acid, and salicylic acid signaling pathway and 56 key transcription factors (TFs), such as MADS-box, bHLH, GRAS, and HSF. The identification of these DEGs provides an important clue for studying the regulation pathway and mechanism of stamen petaloid formation in A. rosea and provides valuable information for molecular plant breeding.

Chromosome-level genome assembly and population genomics reveals crucial selection for subgynoecy development in chieh-qua

Chieh-qua is an important cucurbit crop and very popular in South China and Southeast Asia. Despite its significance, its genetic basis and domestication history are unclear. In this study, we have successfully generated a chromosome-level reference genome assembly for the chieh-qua 'A36' using a hybrid assembly strategy that combines PacBio long reads and Illumina short reads. The assembled genome of chieh-qua is approximately 953.3 Mb in size and is organized into 12 chromosomes, with contig N50 of 6.9 Mb and scaffold N50 of 68.2 Mb. Notably, the chieh-qua genome is comparable in size to the wax gourd genome. Through gene prediction analysis, we have identified a total of 24 593 protein-coding genes in the A36 genome. Additionally, approximately 56.6% (539.3 Mb) of the chieh-qua genome consists of repetitive sequences. Comparative genome analysis revealed that chieh-qua and wax gourd are closely related, indicating a close evolutionary relationship between the two species. Population genomic analysis, employing 129 chieh-qua accessions and 146 wax gourd accessions, demonstrated that chieh-qua exhibits greater genetic diversity compared to wax gourd. We also employed the GWAS method to identify related QTLs associated with subgynoecy, an interested and important trait in chieh-qua. The MYB59 (BhiCQ0880026447) exhibited relatively high expression levels in the shoot apex of four subgynoecious varieties compared with monoecious varieties. Overall, this research provides insights into the domestication history of chieh-qua and offers valuable genomic resources for further molecular research.

The regulatory pathway of transcription factor MYB36 from Trichoderma asperellum Tas653 resistant to poplar leaf blight pathogen Alternaria alternata Aal004

In fungi, MYB transcription factors (TFs) mainly regulate growth, development, and resistance to stress. However, as major disease-resistance TFs, they have rarely been studied in biocontrol fungi. In this study, MYB36 of Trichoderma asperellum Tas653 (Ta) was shown to respond strongly to the stress caused by Alternaria alternata Aa1004. Compared with wild-type Ta (Ta-Wt), the inhibition rate of the MYB36 knockout strain (Ta-Kn) on Aa1004 decreased by 11.06%; the superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities decreased by 82.15 U/g, 0.19 OD470/min/g, and 1631.2 μmol/min/g, respectively. The MYB36 overexpression strain (Ta-Oe) not only enhanced hyperparasitism on Aa1004, caused its hyphae to swell, deform, or even rupture, but also reduced the incidence rate of poplar leaf blight. MYB36 regulates downstream (TFs, detoxification genes, defense genes, and other antifungal-related genes by binding to the cis-acting elements "ACAT" and "ATCG". Zinc finger TFs, as the main antifungal TFs, account for 90% of the total TFs, and Zn37.5 (23.24-) and Zn83.7 (23.18-fold) showed the greatest expression difference when regulated directly by MYB36. The detoxification genes mainly comprised 11 major major facilitator superfamily (MFS) genes, among which MYB36 directly increased the expression levels of three genes by more than 2-3.44-fold. The defense genes mainly encoded cytochrome P450 (P450) and hydrolases. e.g., P45061.3 (2-10.95-), P45060.2 (2-7.07-), and Hyd44.6 (2-2.30-fold). This study revealed the molecular mechanism of MYB36 regulation of the resistance of T. asperellum to A. alternata and provides theoretical guidance for the biocontrol of poplar leaf blight and the anti-disease mechanism of biocontrol fungi.

Rice transcriptional repressor OsTIE1 controls anther dehiscence and male sterility by regulating JA biosynthesis

Proper anther dehiscence is essential for successful pollination and reproduction in angiosperms, and jasmonic acid (JA) is crucial for the process. However, the mechanisms underlying the tight regulation of JA biosynthesis during anther development remain largely unknown. Here, we demonstrate that the rice (Oryza sativa L.) ethylene-response factor-associated amphiphilic repression (EAR) motif-containing protein TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTORS (TCP) INTERACTOR CONTAINING EAR MOTIF PROTEIN1 (OsTIE1) tightly regulates JA biosynthesis by repressing TCP transcription factor OsTCP1/PCF5 during anther development. The loss of OsTIE1 function in Ostie1 mutants causes male sterility. The Ostie1 mutants display inviable pollen, early stamen filament elongation, and precocious anther dehiscence. In addition, JA biosynthesis is activated earlier and JA abundance is precociously increased in Ostie1 anthers. OsTIE1 is expressed during anther development, and OsTIE1 is localized in nuclei and has transcriptional repression activity. OsTIE1 directly interacts with OsTCP1, and overexpression of OsTCP1 caused early anther dehiscence resembling that of Ostie1. JA biosynthesis genes including rice LIPOXYGENASE are regulated by the OsTIE1-OsTCP1 complex. Our findings reveal that the OsTIE1-OsTCP1 module plays a critical role in anther development by finely tuning JA biosynthesis and provide a foundation for the generation of male sterile plants for hybrid seed production.

The genetic control of herkogamy

Herkogamy is the spatial separation of anthers and stigmas within complete flowers, and is a key floral trait that promotes outcrossing in many angiosperms. The degree of separation between pollen-producing anthers and receptive stigmas has been shown to influence rates of self-pollination amongst plants, with a reduction in herkogamy increasing rates of successful selfing in self-compatible species. Self-pollination is becoming a critical issue in horticultural crops grown in environments where biotic pollinators are limited, absent, or difficult to utilise. In these cases, poor pollination results in reduced yield and misshapen fruit. Whilst there is a growing body of work elucidating the genetic basis of floral organ development, the genetic and environmental control points regulating herkogamy are poorly understood. A better understanding of the developmental and regulatory pathways involved in establishing varying degrees of herkogamy is needed to provide insights into the production of flowers more adept at selfing to produce consistent, high-quality fruit. This review presents our current understanding of herkogamy from a genetics and hormonal perspective.

Transcriptional regulation of flavonol biosynthesis in plants

Flavonols are a class of flavonoids that play a crucial role in regulating plant growth and promoting stress resistance. They are also important dietary components in horticultural crops due to their benefits for human health. In past decades, research on the transcriptional regulation of flavonol biosynthesis in plants has increased rapidly. This review summarizes recent progress in flavonol-specific transcriptional regulation in plants, encompassing characterization of different categories of transcription factors (TFs) and microRNAs as well as elucidation of different transcriptional mechanisms, including direct and cascade transcriptional regulation. Direct transcriptional regulation involves TFs, such as MYB, AP2/ERF, and WRKY, which can directly target the key flavonol synthase gene or other early genes in flavonoid biosynthesis. In addition, different regulation modules in cascade transcriptional regulation involve microRNAs targeting TFs, regulation between activators, interaction between activators and repressors, and degradation of activators or repressors induced by UV-B light or plant hormones. Such sophisticated regulation of the flavonol biosynthetic pathway in response to UV-B radiation or hormones may allow plants to fine-tune flavonol homeostasis, thereby balancing plant growth and stress responses in a timely manner. Based on orchestrated regulation, molecular design strategies will be applied to breed horticultural crops with excellent health-promoting effects and high resistance.

Jasmonate signaling pathway confers salt tolerance through a NUCLEAR FACTOR-Y trimeric transcription factor complex in Arabidopsis

Jasmonate (JA) is a well-known phytohormone essential for plant response to biotic stress. Recently, a crucial role of JA signaling in salt resistance has been highlighted; however, the specific regulatory mechanism remains largely unknown. In this study, we found that the NUCLEAR FACTOR-Y (NF-Y) subunits NF-YA1, NF-YB2, and NF-YC9 form a trimeric complex that positively regulates the expression of salinity-responsive genes, whereas JASMONATE-ZIM DOMAIN protein 8 (JAZ8) directly interacts with three subunits and acts as the key repressor to suppress both the assembly of the NF-YA1-YB2-YC9 trimeric complex and the transcriptional activation activity of the complex. When plants encounter high salinity, JA levels are elevated and perceived by the CORONATINE INSENSITIVE (COI) 1 receptor, leading to the degradation of JAZ8 via the 26S proteasome pathway, thereby releasing the activity of the NF-YA1-YB2-YC9 complex, initiating the activation of salinity-responsive genes, such as MYB75, and thus enhancing the salinity tolerance of plants.

A tau class glutathione S-transferase in tea plant, CsGSTU45, facilitates tea plant susceptibility to Colletotrichum camelliae infection mediated by jasmonate signaling pathway

Tea plant [Camellia sinensis (L.) O. Kuntze], as one of the most important commercial crops, frequently suffers from anthracnose caused by Colletotrichum camelliae. The plant-specific tau (U) class of glutathione S-transferases (GSTU) participates in ROS homeostasis. Here, we identified a plant-specific GST tau class gene from tea plant, CsGSTU45, which is induced by various stresses, including C. camelliae infection, by analyzing multiple transcriptomes. CsGSTU45 plays a negative role in disease resistance against C. camelliae by accumulating H2 O2 . JA negatively regulates the resistance of tea plants against C. camelliae, which depends on CsGSTU45. CsMYC2.2, which is the key regulator in the JA signaling pathway, directly binds to and activates the promoter of CsGSTU45. Furthermore, silencing CsMYC2.2 increased disease resistance associated with reduced transcript and protein levels of CsGSTU45, and decreased contents of H2 O2 . Therefore, CsMYC2.2 suppresses disease resistance against C. camelliae by binding to the promoter of the CsGSTU45 gene and activating CsGSTU45. CsJAZ1 interacts with CsMYC2.2. Silencing CsJAZ1 attenuates disease resistance, upregulates the expression of CsMYC2.2 elevates the level of the CsGSTU45 protein, and promotes the accumulation of H2 O2 . As a result, CsJAZ1 interacts with CsMYC2.2 and acts as its repressor to suppress the level of CsGSTU45 protein, eventually enhancing disease resistance in tea plants. Taken together, the results show that the JA signaling pathway mediated by CsJAZ1-CsMYC2.2 modulates tea plant susceptibility to C. camelliae by regulating CsGSTU45 to accumulate H2 O2 .

The Histone Variant H3.3 Is Required for Plant Growth and Fertility in Arabidopsis

Histones are the core components of the eukaryote chromosome, and have been implicated in transcriptional gene regulation. There are three major isoforms of histone H3 in Arabidopsis. Studies have shown that the H3.3 variant is pivotal in modulating nucleosome structure and gene transcription. However, the function of H3.3 during development remains to be further investigated in plants. In this study, we disrupted all three H3.3 genes in Arabidopsis. Two triple mutants, h3.3cr-4 and h3.3cr-5, were created by the CRISPR/Cas9 system. The mutant plants displayed smaller rosettes and decreased fertility. The stunted growth of h3.3cr-4 may result from reduced expression of cell cycle regulators. The shorter stamen filaments, but not the fertile ability of the gametophytes, resulted in reduced fertility of h3.3cr-4. The transcriptome analysis suggested that the reduced filament elongation of h3.3cr-4 was probably caused by the ectopic expression of several JASMONATE-ZIM DOMAIN (JAZ) genes, which are the key repressors of the signaling pathway of the phytohormone jasmonic acid (JA). These observations suggest that the histone variant H3.3 promotes plant growth, including rosette growth and filament elongation.

The transcription factors and pathways underpinning male reproductive development in Arabidopsis

As Arabidopsis flowers mature, specialized cells within the anthers undergo meiosis, leading to the production of haploid microspores that differentiate into mature pollen grains, each containing two sperm cells for double fertilization. During pollination, the pollen grains are dispersed from the anthers to the stigma for subsequent fertilization. Transcriptomic studies have identified a large number of genes expressed over the course of male reproductive development and subsequent functional characterization of some have revealed their involvement in floral meristem establishment, floral organ growth, sporogenesis, meiosis, microsporogenesis, and pollen maturation. These genes encode a plethora of proteins, ranging from transcriptional regulators to enzymes. This review will focus on the regulatory networks that control male reproductive development, starting from flower development and ending with anther dehiscence, with a focus on transcription factors and some of their notable target genes.

Jasmonate activates secondary cell wall biosynthesis through MYC2-MYB46 module

Formation of secondary cell wall (SCW) is tightly regulated spatiotemporally by various developmental and environmental signals. Successful fine-tuning of the trade-off between SCW biosynthesis and stress responses requires a better understanding of how plant growth is regulated under environmental stress conditions. However, the current understanding of the interplay between environmental signaling and SCW formation is limited. The lipid-derived plant hormone jasmonate (JA) and its derivatives are important signaling components involved in various physiological processes including plant growth, development, and abiotic/biotic stress responses. Recent studies suggest that JA is involved in SCW formation but the signaling pathway has not been studied for how JA regulates SCW formation. We tested this hypothesis using the transcription factor MYB46, a master switch for SCW biosynthesis, and JA treatments. Both the transcript and protein levels of MYB46, a master switch for SCW formation, were significantly increased by JA treatment, resulting in the upregulation of SCW biosynthesis. We then show that this JA-induced upregulation of MYB46 is mediated by MYC2, a central regulator of JA signaling, which binds to the promoter of MYB46. We conclude that this MYC2-MYB46 module is a key component of the plant response to JA in SCW formation.

MdbHLH93 confers drought tolerance by activating MdTyDC expression and promoting dopamine biosynthesis

Dopamine and its biosynthesis-limiting enzyme tyrosine decarboxylase (TyDC) play a vital part in mediating plant growth and the response to drought stress. However, the underlying molecular mechanism remains poorly understood. Here, drought stress markedly induced the expression of Malus domestica bHLH93 (MdbHLH93), the apple basic helix-loop-helix transcription factor. Moreover, MdbHLH93 directly bound to the Malus domestica TyDC (MdTyDC) promoter and positively regulated its expression, which resulted in dopamine synthesis and enhanced drought tolerance. Furthermore, the additive effect of overexpressing MdbHLH93 and MdTyDC simultaneously promoted dopamine synthesis and drought tolerance in apples, while the interference of MdbHLH93 inhibited this effect, indicating that MdTyDC-regulated dopamine synthesis and drought tolerance were positively regulated by MdbHLH93. Taken together, these findings suggest the positive regulation of dopamine accumulation by MdbHLH93 through its transcriptional regulation of MdTyDC and show that increased dopamine content confers drought tolerance in apples.

OsJAZ4 Fine-Tunes Rice Blast Resistance and Yield Traits

JAZ proteins function as transcriptional regulators that form a jasmonic acid-isoleucine (JA-Ile) receptor complex with coronatine insensitive 1 (COI1) and regulate plant growth and development. These proteins also act as key mediators in signal transduction pathways that activate the defense-related genes. Herein, the role of OsJAZ4 in rice blast resistance, a severe disease, was examined. The mutation of OsJAZ4 revealed its significance in Magnaporthe oryzae (M. oryzae) resistance and the seed setting rate in rice. In addition, weaker M. oryzae-induced ROS production and expression of the defense genes OsO4g10010, OsWRKY45, OsNAC4, and OsPR3 was observed in osjaz4 compared to Nipponbare (NPB); also, the jasmonic acid (JA) and gibberellin4 (GA4) content was significantly lower in osjaz4 than in NPB. Moreover, osjaz4 exhibited a phenotype featuring a reduced seed setting rate. These observations highlight the involvement of OsJAZ4 in the regulation of JA and GA4 content, playing a positive role in regulating the rice blast resistance and seed setting rate.

Transcription Factors and Their Regulatory Roles in the Male Gametophyte Development of Flowering Plants

Male gametophyte development in plants relies on the functions of numerous genes, whose expression is regulated by transcription factors (TFs), non-coding RNAs, hormones, and diverse environmental stresses. Several excellent reviews are available that address the genes and enzymes associated with male gametophyte development, especially pollen wall formation. Growing evidence from genetic studies, transcriptome analysis, and gene-by-gene studies suggests that TFs coordinate with epigenetic machinery to regulate the expression of these genes and enzymes for the sequential male gametophyte development. However, very little summarization has been performed to comprehensively review their intricate regulatory roles and discuss their downstream targets and upstream regulators in this unique process. In the present review, we highlight the research progress on the regulatory roles of TF families in the male gametophyte development of flowering plants. The transcriptional regulation, epigenetic control, and other regulators of TFs involved in male gametophyte development are also addressed.

From epidermal cells to functional pores: Understanding stomatal development

Stomata, small hydromechanical valves in the leaf epidermis, are fundamental in regulating gas exchange and water loss between plants and the environment. Stomatal development involves a series of coordinated events ranging from the initial cell division that determines the meristemoid mother cells to forming specialized structures such as guard cells. These events are orchestrated by the transcription factors SPEECHLESS, FAMA, and MUTE through signaling networks. The role of plant hormones (e.g., abscisic acid, jasmonic acid, and brassinosteroids) in regulating stomatal development has been elucidated through these signaling cascades. In addition, environmental factors, such as light availability and CO2 concentration, also regulate the density and distribution of stomata in leaves, ultimately affecting overall water use efficiency. In this review, we highlight the mechanisms underlying stomatal development, connecting key signaling processes that activate or inhibit cell differentiation responsible for forming guard cells in the leaf epidermis. The factors responsible for integrating transcription factors, hormonal responses, and the influence of climatic factors on the signaling network that leads to stomatal development in plants are further discussed. Understanding the intricate connections between these factors, including the metabolic regulation of plant development, may enable us to maximize plant productivity under specific environmental conditions in changing climate scenarios.

Partial desensitization of MYC2 transcription factor alters the interaction with jasmonate signaling components and affects specialized metabolism

The activity of bHLH transcription factor MYC2, a key regulator in jasmonate signaling and plant specialized metabolism, is sensitive to repression by JASMONATE-ZIM-domain (JAZ) proteins and co-activation by the mediator subunit MED25. The substitution of a conserved aspartic acid (D) to asparagine (N) in the JAZ-interacting domain (JID) of Arabidopsis MYC2 affects interaction with JAZ, although the mechanism remained unclear. The effects of the conserved residue MYC2D128 on interaction with MED25 have not been investigated. Using tobacco as a model, we generated all possible substitutions of aspartic acid 128 (D128) in NtMYC2a. NtMYC2aD128N partially desensitized the repression by JAZ proteins, while strongly interacting with MED25, resulting in increased expression of nicotine pathway genes and nicotine accumulation in tobacco hairy roots overexpressing NtMYC2aD128N compared to those overexpressing NtMYC2a. The proline substitution, NtMYC2aD128P, negatively affected transactivation and abolished the interaction with JAZ proteins and MED25. Structural modeling and simulation suggest that the overall stability of the JID binding pocket is a predominant cause for the observed effects of substitutions at D128. The D128N substitution has an overall stabilizing effect on the binding pocket, which is destabilized by D128P. Our study offers an innovative tool to increase the production of plant natural products.

MYB24 orchestrates terpene and flavonol metabolism as light responses to anthocyanin depletion in variegated grape berries

Variegation is a rare type of mosaicism not fully studied in plants, especially fruits. We examined red and white sections of grape (Vitis vinifera cv. 'Béquignol') variegated berries and found that accumulation of products from branches of the phenylpropanoid and isoprenoid pathways showed an opposite tendency. Light-responsive flavonol and monoterpene levels increased in anthocyanin-depleted areas in correlation with increasing MYB24 expression. Cistrome analysis suggested that MYB24 binds to the promoters of 22 terpene synthase (TPS) genes, as well as 32 photosynthesis/light-related genes, including carotenoid pathway members, the flavonol regulator HY5 HOMOLOGUE (HYH), and other radiation response genes. Indeed, TPS35, TPS09, the carotenoid isomerase gene CRTISO2, and HYH were activated in the presence of MYB24 and MYC2. We suggest that MYB24 modulates ultraviolet and high-intensity visible light stress responses that include terpene and flavonol synthesis and potentially affects carotenoids. The MYB24 regulatory network is developmentally triggered after the onset of berry ripening, while the absence of anthocyanin sunscreens accelerates its activation, likely in a dose-dependent manner due to increased radiation exposure. Anthocyanins and flavonols in variegated berry skins act as effective sunscreens but for different wavelength ranges. The expression patterns of stress marker genes in red and white sections of 'Béquignol' berries strongly suggest that MYB24 promotes light stress amelioration but only partly succeeds during late ripening.

MYB transcription factors and their roles in the male reproductive development of flowering plants

As one of the largest transcription factor families with complex functional differentiation in plants, the MYB transcription factors (MYB TFs) play important roles in the physiological and biochemical processes of plant growth and development. Male reproductive development, an essential part of sexual reproduction in flowering plants, is undoubtedly regulated by MYB TFs. In this review, we summarize the roles of the MYB TFs involved in the three stages of male reproductive development: pollen grains formation and maturation, filament elongation and anther dehiscence, and fertilization. Also, the potential downstream target genes and upstream regulators of these MYB TFs are discussed. Furthermore, we propose the underlying regulatory mechanisms of these MYB TFs: (1) A complex network of MYB TFs regulates various aspects of male reproductive development; (2) MYB homologous genes in different species may be functionally conserved or differentiated; (3) MYB TFs often form regulatory complexes with bHLH TFs.

AcbHLH144 transcription factor negatively regulates phenolic biosynthesis to modulate pineapple internal browning

Internal browning (IB), a major physiological disorder of pineapples, usually happens in postharvest processes, but the underlying mechanism remains elusive. The bHLH transcription factors are involved in regulating various biological processes, but whether they could regulate tissue browning in fruit during storage remains unknown. Here we showed that the phenolic biosynthesis pathway was activated in pineapples showing IB following 9 days of storage. AcbHLH144 expression was the highest of the 180 transcription factors identified, downregulated in pineapple with IB, and negatively correlated with the major phenolic biosynthetic genes. AcbHLH144 was shown to be localized in the nucleus and its transient overexpression in pineapples and overexpression in Arabidopsis decreased phenolic biosynthesis. The yeast one-hybrid assay and electrophoretic mobility shift assay showed that AcbHLH144 directly bound to the Ac4CL5 promoter and the dual-luciferase reporter assay showed that it inactivated Ac4CL5 transcription. These results strongly suggest AcbHLH144 as a repressor for phenolic biosynthesis. Abscisic acid (ABA) alleviated IB, reduced phenolic accumulation, and downregulated phenolic biosynthetic genes, including Ac4CL5. Transcriptomic analysis showed that AcbHLH144 was the most upregulated of all 39 bHLHs in response to ABA. ABA enhanced AcbHLH144 expression, reduced phenolic contents, and downregulated phenolic biosynthetic genes in pineapples transiently overexpressing AcbHLH144. Moreover, ABA enhanced enzyme activity of GUS driven by the AcbHLH144 promoter. These results showed that AcbHLH144 as a repressor for phenolic biosynthesis could be activated by ABA. Collectively, the work demonstrated that AcbHLH144 negatively regulated phenolic biosynthesis via inactivating Ac4CL5 transcription to modulate pineapple IB. The findings provide novel insight into the role of AcbHLH144 in modulating pineapple IB during postharvest processes.

The Arabidopsis F-box protein SKP1-INTERACTING PARTNER 31 modulates seed maturation and seed vigor by targeting JASMONATE ZIM DOMAIN proteins independently of jasmonic acid-isoleucine

F-box proteins have diverse functions in eukaryotic organisms, including plants, mainly targeting proteins for 26S proteasomal degradation. Here, we demonstrate the role of the F-box protein SKP1-INTERACTING PARTNER 31 (SKIP31) from Arabidopsis (Arabidopsis thaliana) in regulating late seed maturation events, seed vigor, and viability through biochemical and genetic studies using skip31 mutants and different transgenic lines. We show that SKIP31 is predominantly expressed in seeds and that SKIP31 interacts with JASMONATE ZIM DOMAIN (JAZ) proteins, key repressors in jasmonate (JA) signaling, directing their ubiquitination for proteasomal degradation independently of coronatine/jasmonic acid-isoleucine (JA-Ile), in contrast to CORONATINE INSENSITIVE 1, which sends JAZs for degradation in a coronatine/JA-Ile dependent manner. Moreover, JAZ proteins interact with the transcription factor ABSCISIC ACID-INSENSITIVE 5 (ABI5) and repress its transcriptional activity, which in turn directly or indirectly represses the expression of downstream genes involved in the accumulation of LATE EMBRYOGENESIS ABUNDANT proteins, protective metabolites, storage compounds, and abscisic acid biosynthesis. However, SKIP31 targets JAZ proteins, deregulates ABI5 activity, and positively regulates seed maturation and consequently seed vigor. Furthermore, ABI5 positively influences SKIP31 expression, while JAZ proteins repress ABI5-mediated transactivation of SKIP31 and exert feedback regulation. Taken together, our findings reveal the role of the SKIP31-JAZ-ABI5 module in seed maturation and consequently, establishment of seed vigor.

Genome-wide association study of ear tip barrenness in waxy maize

Ear tip-barrenness (ETB), which results from aborted kernels or infertile florets at the ear tip, is an undesirable factor affecting the yield and quality of waxy maize. To uncover the genetic basis of ETB, a genome-wide association study (GWAS) was conducted using the genotype with 27,354 SNPs and phenotype with three environments. Five SNPs that distributed on chromosomes 1, 3 and 6, were identified to be significantly associated with ETB based on the threshold of false discovery rate (FDR) at 0.05. Among these significant loci, three SNPs were clustered together and colocalized with genomic regions previously reported. The average length of ETB decreased almost linearly from the inbred lines containing no favorable alleles across the three loci (1.75 cm) to those with one (1.18 cm), two (0.94 cm) and three (0.65 cm) favorable alleles. Moreover, three important genes, Zm00001d030028, Zm00001d041510 and Zm00001d038676 were predicted for three significant QTLs, respectively. These results promote the understanding genetic basis for ETB and will be useful for breeding waxy maize varieties with high-quality and high-yield.