RAV transcription factors are essential for disease resistance against cassava bacterial blight via activation of melatonin biosynthesis genes

Transcriptomic and metabolomic analyses unveil TaASMT3-mediated wheat resistance against stripe rust by promoting melatonin biosynthesis

Plants have evolved a series of complicated defense mechanisms to counteract pathogen invasions. Although many studies have provided molecular evidence of resistance proteins and downstream signal transduction networks, the mechanisms by which plants resist pathogens remain poorly understood at the metabolite level. Here, we performed transcriptomic analyses of wheat leaves infected with Puccinia striiformis f. sp. tritici (Pst), the causal agent of wheat stripe rust. Functional enrichment analysis of identified differentially expressed genes (DEGs) revealed the strongest resistance responses at 24 h post-inoculation (hpi) in the incompatible wheat-Pst interaction system. Integrated with the metabolomics data at 24 hpi, we found that the amino acid metabolic pathways appeared to be directly involved in stripe rust resistance. Among these, five differentially abundant metabolites (DAMs) indole, tryptophan, tryptamine, N-Methylserotonin, and 5-Methoxyindoleacetate were enriched to the biosynthesis pathway of melatonin, a branch of tryptophan metabolism. Subsequent UPLC-MS/MS analysis confirmed that melatonin was highly accumulated in the incompatible wheat-Pst system, but not in the compatible interaction system. Exogenous melatonin treatment induced wheat resistance to Pst. The most significantly upregulated melatonin biosynthesis-related gene in the incompatible wheat-Pst system was TaASMT3, which encodes an acetylserotonin O-methyltransferase. Virus-induced gene silencing analysis revealed that knocking down TaASMT3 reduced wheat resistance to stripe rust, further suggesting a positive role of melatonin in wheat resistance to Pst. Taken together, these data suggest that melatonin was accumulated during Pst infection to activate wheat defense responses, offering a new perspective for elucidation of wheat stripe rust resistance based on metabolic dynamics.

Exogenous melatonin and salicylic acid enhance postharvest quality and boost antioxidant capacity in Vitis vinifera cv. 'Cuibao seedless' grape berries

The quality of table grape is a key factor influencing consumer purchasing decisions and market prices. However, grape is soft, juicy, and prone to rotting and deterioration, making them unsuitable for storage. To ensure grape quality and extend its shelf life, this study applied salicylic acid (SA), melatonin (MT), and SA + MT treatments to postharvest mature grape. The appearance index, antioxidant content, enzyme activity, and gene expression levels of fruits stored at low temperatures for varying durations were measured. The results showed that SA, MT, and SA + MT treatments effectively reduced the browning index(BI), minimized weight loss(WL), and preserved the contents of ascorbic acid (AsA), soluble sugars (SS), and soluble proteins (SP). Compared to the control group, the contents of total phenols (TP), flavonoids (TF), proline (Pro), and the activities of superoxide dismutase (SOD), catalase (CAT), and phenylalanine ammonia lyase (PAL) were higher in each hormone treatment group, while malondialdehyde (MDA) levels and the activities of polyphenol oxidase (PPO) and peroxidase (POD) were lower. Principal component analysis (PCA) revealed that MT treatment was most effective, followed by SA and SA + MT treatments. Correlation analysis indicated a positive correlation between the contents of TP and TF and their associated structural enzymes. Furthermore, the expression levels of genes related to phenolic and flavonoid synthesis (VvPAL, VvCHI, VvF3H2, VvANR) were significantly upregulated in all treatment groups. This study provides a foundation for further exploring the effects of hormones on postharvest grape.

MsbZIP55 regulates salinity tolerance by modulating melatonin biosynthesis in alfalfa

Soil salinity is a severe abiotic stress that damages plant growth and development. As an antioxidant and free radical scavenger, melatonin is well known for helping plants survive abiotic conditions, including salinity stress. Here, we report that the salt-related gene MsSNAT1, encoding a rate-limiting melatonin biosynthesis enzyme, is located in the chloroplast and contributes to salinity stress tolerance in alfalfa. We found that the MsSNAT1 overexpressing alfalfa lines exhibited higher endogenous melatonin levels and increased tolerance to salt stress by promoting antioxidant systems and improving ion homeostasis. Furthermore, through a combination of transcriptome sequencing, dual-luciferase assays and transgenic analysis, we identified that the basic leucine zipper (bZIP) transcription factor, MsbZIP55, is associated with salt response and MsSNAT1 expression. EMSA analysis and ChIP-qPCR uncovered that MsbZIP55 can recognize and directly bind to the MsSNAT1 promoter in vitro and in vivo. MsbZIP55 acts as a negative regulator of MsSNAT1 expression, thereby reducing melatonin biosynthesis. Morphological analysis revealed that overexpressing MsbZIP55 conferred salt sensitivity to transgenic alfalfa through a higher Na+/K+ ratio and lower antioxidant activities, which could be alleviated by applying exogenous melatonin. Silencing of MsbZIP55 by RNA interference in alfalfa resulted in higher expression of MsSNAT1 and promoted salt tolerance by enhancing the antioxidant system enzyme activities and ion homeostasis. Our findings indicate that the MsbZIP55-MsSNAT1 module plays a crucial role in regulating melatonin biosynthesis in alfalfa while facilitating protection against salinity stress. These results shed light on the regulatory mechanism of melatonin biosynthesis related to the salinity stress response in alfalfa.

Evolutionary-Distinct Viral Proteins Subvert Rice Broad-Spectrum Antiviral Immunity Mediated by the RAV15-MYC2 Module

A variety of plant viruses employ different virulence strategies to achieve successful infection, resulting in abnormal plant development. However, the common pathogenicity of distinct viruses has rarely been studied. Here, it is shown that a plant-specific RAV-type transcription factor, OsRAV15, is specifically targeted by several distinct viral proteins for facilitating viral infection. OsRAV15 is found to activate jasmonic acid (JA)-mediated broad-spectrum antiviral immunity by physically associating with JA signaling essential components OsMYC2-OsJAZ complex. To facilitate viral infection, evolutionarily distinct viral proteins encoded by diverse rice viruses generally disrupt the OsRAV15-OsMYC2 complex to attenuate activation of JA signaling. Together, the results reveal a common counter-defense strategy used by different viruses to suppress the OsRAV15-OsMYC2 module that plays a vital role in fine-tuning JA-mediated antiviral defense.

The melatonin synthase-encoding gene ASMT mediates poplar resistance to drought stress and fungi Dothiorella gregaria

In recent years, the increase in extreme climates, such as persistent high temperatures and drought, has adversely affected the growth and development of fast-growing trees. Melatonin (MT) plays an important role in plant responses to biotic and abiotic stresses, yet there is a lack of research on the specific role of limiting enzyme genes for MT biosynthesis in fast-growing woody plants. In this study, we investigated the function of PtoASMT, a key rate-limiting enzyme encoding gene for MT biosynthesis, which can be induced by drought, salt, and the phytohormones ABA, SA and JA. Our results show that: (1) PtoASMT was widely expressed in all tissues of poplar, but was highly expressed in petioles, moderately expressed in roots, stems, shoots and young leaves, exhibiting a typical diurnal expression rhythm in leaves, with the encoded protein localized on chloroplasts; (2) the content of MT was significantly promoted in overexpressing PtoASMT transgenic poplar plants, but there were no obvious differences in their growth and development; (3) overexpressing PtoASMT plants exhibited stronger drought tolerance, accumulating less reactive oxygen species (ROS) under drought stress relative to wild-type plants, whereas knockout PtoASMT plants were more sensitive and accumulated more ROS; (4) overexpressing PtoASMT plants were more resistant to fungi Dothiorella gregaria than WT plants, while knockout plants showed higher sensitivity; meanwhile, the expression of disease resistance-related genes (PRs and JAZ10) was significantly altered. We conclude that PtoASMT enhances the resistance of poplar to drought and Dothiorella gregaria by mediating MT biosynthesis in poplar. These findings contribute to a better understanding the role of ASMT gene in MT accumulation and stress resistance in poplar.

The transcription factor CitPH4 regulates plant defense-related metabolite biosynthesis in citrus

Wild citrus (Citrus L.) exhibits high disease resistance accompanied by high-acidity fruit, whereas cultivated citrus produces tastier fruit but is more susceptible to disease. This is a common phenomenon, but the underlying molecular mechanisms remain unknown. Citrus PH4 (CitPH4) is a key transcription factor promoting citric acid accumulation in fruits. Accordingly, CitPH4 expression decreased during citrus domestication, along with a reduction in citric acid levels. Here, we demonstrate that a CitPH4-knockout mutant exhibits an acidless phenotype and displays substantially lower resistance to citrus diseases. Metabolome and transcriptome analyses of CitPH4-overexpressing citrus callus, Arabidopsis, and CitPH4-knockout citrus fruits revealed that quercetin, pipecolic acid (Pip), and N-hydroxypipecolic acid (NHP) are pivotal defense-related metabolites. Application of quercetin and Pip inhibited the growth of Xcc and Penicillium italicum, while NHP inhibited the growth of P. italicum and Huanglongbing. Biochemical experiments demonstrated that CitPH4 enhances the expression of quercetin and NHP biosynthesis genes by binding to their promoters. Moreover, Pip and quercetin contents were positively associated with citric acid content in the pulp of fruits from natural citrus populations. Finally, the heterologous expression of CitPH4 in Arabidopsis promoted the expression of stress response genes and enhanced its resistance to the fungal pathogen Botrytis cinerea. The overexpression of CitPH4 in tobacco (Nicotiana tabacum) enhanced disease resistance. This study reveals the mechanism by which CitPH4 regulates disease resistance and fruit acidity, providing a conceptual strategy to control fruit acidity and resistance to devastating diseases.

The potential of melatonin and its crosstalk with other hormones in the fight against stress

Climate change not only leads to high temperatures, droughts, floods, storms and declining soil quality, but it also affects the spread and mutation of pests and diseases, which directly influences plant growth and constitutes a new challenge to food security. Numerous hormones like auxin, ethylene and melatonin, regulate plant growth and development as well as their resistance to environmental stresses. To mitigate the impact of diverse biotic and abiotic stressors on crops, single or multiple phytohormones in combination have been applied. Melatonin is a multifunctional signaling molecule engaged in the development and stress response of plants. In the current review, we discuss the synthesis and action of melatonin, as well as its utilization for plant resistance to different stresses from the perspective of practical application. Simultaneously, we elucidate the regulatory effects and complex mechanisms of melatonin and other plant hormones on the growth of plants, explore the practical applications of melatonin in combination with other phytohormones in crops. This will aid in the planning of management strategies to protect plants from damage caused by environmental stress.

Overexpression of the RAV Transcription Factor OsAAT1 Confers Enhanced Arsenic Tolerance by Modulating Auxin Hemostasis in Rice

Characterization of arsenic (As)-responsive genes is fundamental to solving the issue of As contamination in rice. Herein, we establish the involvement of an RAV transcription factor OsAAT1 (Arsenic Accumulation and Tolerance 1) in regulating As response in rice. The expression of OsAAT1 is significantly higher in roots and stems of rice seedlings and is clearly upregulated by higher concentrations of arsenite [As(III)]. Compared with wild-type (WT) plants, OsAAT1-overexpressed transgenic lines (OE-OsAAT1) exhibit tolerance, while OsAAT1-knockout mutants (Osaat1) are sensitive to As(III) stress. Notably, the application of exogenous 1-naphthylacetic acid (NAA) greatly enhances the As tolerance of WT and transgenic lines, with stronger effects on OE-OsAAT1. The change in OsAAT1 expression leads to the alteration of As and auxin accumulation in transgenic plants by regulating the expression of OsLsi1, OsLsi2, OsCRL4, and OsAUX1 genes. Moreover, overexpression of OsAAT1 accelerates ROS scavenging and phytochelatins (PCs) synthesis, especially with the addition of exogenous NAA. OsAAT1 localizes in the nucleus and works as a transcriptional suppressor. OsGH3-12, belonging to the auxin-responsive GH3 gene family, is the downstream target gene of OsAAT1, whose expression is extensively downregulated by As(III). These findings provide new insights into As response via auxin signaling pathway in rice.

Genome-wide analysis of the AP2/ERF gene family in Pennisetum glaucum and the negative role of PgRAV_01 in drought tolerance

APETALA2/ethylene-responsive (AP2/ERF) plays crucial roles in resisting diverse stresses and in regulating plant growth and development. However, little is known regarding the structure and function of the AP2/ERF genes in pearl millet (Pennisetum glaucum). The AP2/ERF gene family may be involved in the development and maintenance of P. glaucum resilience to abiotic stresses, central to its role as a vital forage and cereal crop. In this study, PgAP2/ERF family members were identified and comprehensive bioinformatics analyses were performed, including determination of phylogenetic relationships, gene structures, conserved motifs, chromosomal localization, gene duplication, expression pattern, protein interaction network, and functional characterization of PgRAV_01 (Related to ABI3/VP1). In total, 78 PgAP2/ERF members were identified in the P. glaucum genome and classified into five subfamilies: AP2, ERF, DREB, RAV, and soloist. Members within the same clade of the PgAP2/ERF family showed similar gene structures and motif compositions. Six duplication events were identified in the PgAP2/ERF family; calculation of Ka/Ks values showed that purification selection dominated the evolution of PgAP2/ERFs. Subsequently, a potential interaction network of PgAP2/ERFs was generated to predict the interaction relationships. Additionally, abiotic stress expression analysis showed that most PgAP2/ERFs were induced in response to drought and heat stresses. Furthermore, overexpression of PgRAV_01 negatively regulated drought tolerance in Nicotiana benthamiana by reducing its antioxidant capacity and osmotic adjustment. Taken together, these results provide valuable insights into the characteristics and functions of PgAP2/ERF genes, with implications for abiotic stress tolerance, and will ultimately contribute to the genetic improvement of cereal crop breeding.

A novel RAV transcription factor from pear interacts with viral RNA-silencing suppressors to inhibit viral infection

In plants, RNA silencing constitutes a strong defense against viral infection, which viruses counteract with RNA-silencing suppressors (RSSs). Understanding the interactions between viral RSSs and host factors is crucial for elucidating the molecular arms race between viruses and host plants. We report that the helicase motif (Hel) of the replicase encoded by apple stem grooving virus (ASGV)-the main virus affecting pear trees in China-is an RSS that can inhibit both local and systemic RNA silencing, possibly by binding double-stranded (ds) siRNA. The transcription factor related to ABSCISIC ACID INSENSITIVE3/VIVIPAROUS1 from pear (PbRAV1) enters the cytoplasm and binds Hel through its C terminus, thereby attenuating its RSS activity by reducing its binding affinity to 21- and 24-nt ds siRNA, and suppressing ASGV infection. PbRAV1 can also target p24, an RSS encoded by grapevine leafroll-associated virus 2 (GLRaV-2), with similar negative effects on p24's suppressive function and inhibition of GLRaV-2 infection. Moreover, like the positive role of the PbRAV1 homolog from grapevine (VvRAV1) in p24's previously reported RSS activity, ASGV Hel can also hijack VvRAV1 and employ the protein to sequester 21-nt ds siRNA, thereby enhancing its own RSS activity and promoting ASGV infection. Furthermore, PbRAV1 neither interacts with CP, an RSS encoded by grapevine inner necrosis virus, nor has any obvious effect on CP's RSS activity. Our results identify an RSS encoded by ASGV and demonstrate that PbRAV1, representing a novel type of RAV transcription factor, plays a defensive role against viral infection by targeting viral RSSs.

Melatonin Enhances Heat Tolerance via Increasing Antioxidant Enzyme Activities and Osmotic Regulatory Substances by Upregulating zmeno1 Expression in Maize (Zea mays L.)

Heat stress severely affects the yield and quality of maize. Melatonin (N-acetyl-5-methoxy-tryptamin, MT) plays an important role in various types of stress resistance in plants, including heat tolerance. Enolase (ENO, 2-phospho-D-glycerate hydrolyase) contributes to plant growth, development, and stress response. As of now, the molecular mechanisms by which MT and ENO1 affect heat tolerance are unknown. In our research, we have revealed that heat stress (H) and heat stress + MT (MH) treatment upregulate ZmENO1 expression levels by 15 and 20 times, respectively. ZmENO1 overexpression and mutant maize lines were created by transgenic and genome editing. These results illustrate that heat stress has a significant impact on the growth of maize at the seedling stage. However, ZmENO1-OE lines showed a lower degree of susceptibility to heat stress, whereas the mutant exhibited the most severe effects. Under heat stress, exogenous application of MT improves heat resistance in maize. The ZmENO1-OE lines exhibited the best growth and highest survival rate, while the zmeno1 mutants showed the least desirable results. Following treatment with H and MH, the level of MT in ZmENO1-OE lines exhibited the greatest increase and reached the maximum value, whereas the level of MT in the zmeno1 mutant was the lowest. Heat stress decreased the maize's relative water content and fresh weight, although ZmENO1-OE lines had the highest and zmeno1 mutants had the lowest. Heat stress led to an increase in the levels of MDA, hydrogen peroxide, and superoxide in all plants. Additionally, the ionic permeability and osmotic potential of the plants were significantly increased. However, the levels of MT were decreased in all plants, with the greatest decrease observed in the ZmENO1-OE lines. Interestingly, the zmeno1 mutant plants had the highest expression levels of MT. Heat stress-induced upregulation of ZmSOD, ZmPOD, ZmAPX, ZmCAT, ZmP5CS, and ZmProDH in all plants. However, the ZmENO1-OE lines exhibited the greatest increase in expression levels, while the zmeno1 mutants showed the lowest increase following MT spraying. The patterns of SOD, POD, APX, and CAT enzyme activity, as well as proline and soluble protein content, aligned with the variations in the expression levels of these genes. Our findings indicate that MT can upregulate the expression of the ZmENO1 gene. Upregulating the ZmENO1 gene resulted in elevated expression levels of ZmSOD, ZmPOD, ZmAPX, ZmCAT, ZmP5CS, and ZmProDH. This led to increased activity of antioxidant enzymes and higher levels of osmoregulatory substances. Consequently, it mitigated the cell membrane damage caused by heat stress and ultimately improved the heat resistance of maize. The results of this study provide genetic resources for molecular design breeding and lay a solid foundation for further exploring the molecular mechanism of MT regulation of heat stress tolerance in maize.

Revealing the Effects of Zinc Sulphate Treatment on Melatonin Synthesis and Regulatory Gene Expression in Germinating Hull-Less Barley through Transcriptomic Analysis

This study investigated the transcriptomic mechanisms underlying melatonin accumulation and the enhancement of salt tolerance in hull-less barley seeds subjected to zinc sulphate stress. Following zinc sulphate treatment, hull-less barley seeds demonstrated increased melatonin accumulation and improved salt tolerance. Through transcriptome analysis, the study compared gene expression alterations in seeds (using the first letter of seed, this group is marked as 'S'), seeds treated with pure water (as the control group, is marked as 'C'), and germinated seeds exposed to varying concentrations of zinc sulphate (0.2 mM and 0.8 mM, the first letter of zinc sulphate, 'Z', is used to mark groups 'Z1' and 'Z2'). The analysis revealed that 8176, 759, and 622 differentially expressed genes (DEGs) were identified in the three comparison groups S.vs.C, C.vs.Z1, and C.vs.Z2, respectively. Most of the DEGs were closely associated with biological processes, including oxidative-stress response, secondary metabolite biosynthesis, and plant hormone signaling. Notably, zinc sulphate stress influenced the expression levels of Tryptophan decarboxylase 1 (TDC1), Acetylserotonin O-methyltransferase 1 (ASMT1), and Serotonin N-acetyltransferase 2 (SNAT2), which are key genes involved in melatonin synthesis. Furthermore, the expression changes of genes such as Probable WRKY transcription factor 75 (WRKY75) and Ethylene-responsive transcription factor ERF13 (EFR13) exhibited a strong correlation with fluctuations in melatonin content. These findings contribute to our understanding of the mechanisms underlying melatonin enrichment in response to zinc sulphate stress.

Phytomelatonin: From Intracellular Signaling to Global Horticulture Market

Melatonin (N-acetyl-5-methoxytryptamine), a well-known mammalian hormone, has been having a great relevance in the Plant World in recent years. Many of its physiological actions in plants are leading to possible features of agronomic interest, especially those related to improvements in tolerance to stressors and in the postharvest life of fruits and vegetables. Thus, through the exogenous application of melatonin or by modifying the endogenous biosynthesis of phytomelatonin, some change can be made in the functional levels of melatonin in tissues and their responses. Also, acting in the respective phytomelatonin biosynthesis enzymes, regulating the expression of tryptophan decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), serotonin N-acetyltransferase (SNAT), N-acetylserotonin O-methyltransferase (ASMT), and caffeic acid O-methyltransferase (COMT), and recently the possible action of deacetylases on some intermediates offers promising opportunities for improving fruits and vegetables in postharvest and its marketability. Other regulators/effectors such as different transcription factors, protein kinases, phosphatases, miRNAs, protein-protein interactions, and some gasotransmitters such as nitric oxide or hydrogen sulfide were also considered in an exhaustive vision. Other interesting aspects such as the role of phytomelatonin in autophagic responses, the posttranslational reprogramming by protein-phosphorylation, ubiquitylation, SUMOylation, PARylation, persulfidation, and nitrosylation described in the phytomelatonin-mediated responses were also discussed, including the relationship of phytomelatonin and several plant hormones, for chilling injury and fungal decay alleviating. The current data about the phytomelatonin receptor in plants (CAND2/PMTR1), the effect of UV-B light and cold storage on the postharvest damage are presented and discussed. All this on the focus of a possible new action in the preservation of the quality of fruits and vegetables.

Identification and expression analyses of B3 genes reveal lineage-specific evolution and potential roles of REM genes in pepper

BACKGROUND

The B3 gene family, one of the largest plant-specific transcription factors, plays important roles in plant growth, seed development, and hormones. However, the B3 gene family, especially the REM subfamily, has not been systematically and functionally studied.

RESULTS

In this study, we performed genome-wide re-annotation of B3 genes in five Solanaceae plants, Arabidopsis thaliana, and Oryza sativa, and finally predicted 1,039 B3 genes, including 231 (22.2%) newly annotated genes. We found a striking abundance of REM genes in pepper species (Capsicum annuum, Capsicum baccatum, and Capsicum chinense). Comparative motif analysis revealed that REM and other subfamilies (ABI3/VP1, ARF, RAV, and HSI) consist of different amino acids. We verified that the large number of REM genes in pepper were included in the specific subgroup (G8) through the phylogenetic analysis. Chromosome location and evolutionary analyses suggested that the G8 subgroup genes evolved mainly via a pepper-specific recent tandem duplication on chromosomes 1 and 3 after speciation between pepper and other Solanaceae. RNA-seq analyses suggested the potential functions of REM genes under salt, heat, cold, and mannitol stress conditions in pepper (C. annuum).

CONCLUSIONS

Our study provides evolutionary and functional insights into the REM gene family in pepper.

Coat protein of cassava common mosaic virus targets RAV1 and RAV2 transcription factors to subvert immunity in cassava

Cassava common mosaic virus (CsCMV, genus Potexvirus) is a prevalent virus associated with cassava mosaic disease, so it is essential to elucidate the underlying molecular mechanisms of the coevolutionary arms race between viral pathogenesis and the cassava (Manihot esculenta Crantz) defense response. However, the molecular mechanism underlying CsCMV infection is largely unclear. Here, we revealed that coat protein (CP) acts as a major pathogenicity determinant of CsCMV via a mutant infectious clone. Moreover, we identified the target proteins of CP-related to abscisic acid insensitive3 (ABI3)/viviparous1 (VP1) (MeRAV1) and MeRAV2 transcription factors, which positively regulated disease resistance against CsCMV via transcriptional activation of melatonin biosynthetic genes (tryptophan decarboxylase 2 (MeTDC2), tryptamine 5-hydroxylase (MeT5H), N-aceylserotonin O-methyltransferase 1 (MeASMT1)) and MeCatalase6 (MeCAT6) and MeCAT7. Notably, the interaction between CP, MeRAV1, and MeRAV2 interfered with the protein phosphorylation of MeRAV1 and MeRAV2 individually at Ser45 and Ser44 by the protein kinase, thereby weakening the transcriptional activation activity of MeRAV1 and MeRAV2 on melatonin biosynthetic genes, MeCAT6 and MeCAT7 dependent on the protein phosphorylation of MeRAV1 and MeRAV2. Taken together, the identification of the CP-MeRAV1 and CP-MeRAV2 interaction module not only illustrates a molecular mechanism by which CsCMV orchestrates the host defense system to benefit its infection and development but also provides a gene network with potential value for the genetic improvement of cassava disease resistance.

CRISPR/Cas9: an advanced platform for root and tuber crops improvement

Root and tuber crops (RTCs), which include cassava, potato, sweet potato, and yams, principally function as staple crops for a considerable fraction of the world population, in addition to their diverse applications in nutrition, industry, and bioenergy sectors. Even then, RTCs are an underutilized group considering their potential as industrial raw material. Complexities in conventional RTC improvement programs curb the extensive exploitation of the potentials of this group of crop species for food, energy production, value addition, and sustainable development. Now, with the advent of whole-genome sequencing, sufficient sequence data are available for cassava, sweet potato, and potato. These genomic resources provide enormous scope for the improvement of tuber crops, to make them better suited for agronomic and industrial applications. There has been remarkable progress in RTC improvement through the deployment of new strategies like gene editing over the last decade. This review brings out the major areas where CRISPR/Cas technology has improved tuber crops. Strategies for genetic transformation of RTCs with CRISPR/Cas9 constructs and regeneration of edited lines and the bottlenecks encountered in their establishment are also discussed. Certain attributes of tuber crops requiring focus in future research along with putative editing targets are also indicated. Altogether, this review provides a comprehensive account of developments achieved, future lines of research, bottlenecks, and major experimental concerns regarding the establishment of CRISPR/Cas9-based gene editing in RTCs.

Molecular identification and functional characterization of a transcription factor GeRAV1 from Gelsemium elegans

BACKGROUND

Gelsemium elegans is a traditional Chinese medicinal plant and temperature is one of the key factors affecting its growth. RAV (related to ABI3/VP1) transcription factor plays multiple roles in higher plants, including the regulation of plant growth, development, and stress response. However, RAV transcription factor in G. elegans has not been reported.

RESULTS

In this study, three novel GeRAV genes (GeRAV1-GeRAV3) were identified from the transcriptome of G. elegans under low temperature stress. Phylogenetic analysis showed that GeRAV1-GeRAV3 proteins were clustered into groups II, IV, and V, respectively. RNA-sequencing (RNA-seq) and real-time quantitative PCR (qRT-PCR) analyses indicated that the expression of GeRAV1 and GeRAV2 was increased in response to cold stress. Furthermore, the GeRAV1 gene was successfully cloned from G. elegans leaf. It encoded a hydrophilic, unstable, and non-secretory protein that contained both AP2 and B3 domains. The amino acid sequence of GeRAV1 protein shared a high similarity of 81.97% with Camptotheca acuminata CaRAV. Subcellular localization and transcriptional self-activation experiments demonstrated that GeRAV1 was a nucleoprotein without self-activating activity. The GeRAV1 gene was constitutively expressed in the leaves, stems, and roots of the G. elegans, with the highest expression levels in roots. In addition, the expression of the GeRAV1 gene was rapidly up-regulated under abscisic acid (ABA), salicylic acid (SA), and methyl jasmonate (MeJA) stresses, suggesting that it may be involved in hormonal signaling pathways. Moreover, GeRAV1 conferred improved cold and sodium chloride tolerance in Escherichia coli Rosetta cells.

CONCLUSIONS

These findings provided a foundation for further understanding on the function and regulatory mechanism of the GeRAV1 gene in response to low-temperature stress in G. elegans.

SmRAV1, an AP2 and B3 Transcription Factor, Positively Regulates Eggplant's Response to Salt Stress

Salt stress is a lethal abiotic stress threatening global food security on a consistent basis. In this study, we identified an AP2 and B3 domain-containing transcription factor (TF) named SmRAV1, and its expression levels were significantly up-regulated by NaCl, abscisic acid (ABA), and hydrogen peroxide (H2O2) treatment. High expression of SmRAV1 was observed in the roots and sepal of mature plants. The transient expression assay in Nicotiana benthamiana leaves revealed that SmRAV1 was localized in the nucleus. Silencing of SmRAV1 via virus-induced gene silencing (VIGS) decreased the tolerance of eggplant to salt stress. Significant down-regulation of salt stress marker genes, including SmGSTU10 and SmNCED1, was observed. Additionally, increased H2O2 content and decreased catalase (CAT) enzyme activity were recorded in the SmRAV1-silenced plants compared to the TRV:00 plants. Our findings elucidate the functions of SmRAV1 and provide opportunities for generating salt-tolerant lines of eggplant.

The RAV transcription factor TEMPRANILLO1 involved in ethylene-mediated delay of chrysanthemum flowering

TEMPRANILLO1 (TEM1) is a transcription factor belonging to related to ABI3 and VP1 family, which is also known as ethylene response DNA-binding factor 1 and functions as a repressor of flowering in Arabidopsis. Here, a putative homolog of AtTEM1 was isolated and characterized from chrysanthemum, designated as CmTEM1. Exogenous application of ethephon leads to an upregulation in the expression of CmTEM1. Knockdown of CmTEM1 promotes floral initiation, while overexpression of CmTEM1 retards floral transition. Further phenotypic observations suggested that CmTEM1 involves in the ethylene-mediated inhibition of flowering. Transcriptomic analysis established that expression of the flowering integrator CmAFL1, a member of the APETALA1/FRUITFULL subfamily, was downregulated significantly in CmTEM1-overexpressing transgenic plants compared with wild-type plants but was verified to be upregulated in amiR-CmTEM1 lines by quantitative RT-PCR. In addition, CmTEM1 is capable of binding to the promoter of the CmAFL1 gene to inhibit its transcription. Moreover, the genetic evidence supported the notion that CmTEM1 partially inhibits floral transition by targeting CmAFL1. In conclusion, these findings demonstrate that CmTEM1 acts as a regulator of ethylene-mediated delayed flowering in chrysanthemum, partly through its interaction with CmAFL1.

Sweet cherry AP2/ERF transcription factor, PavRAV2, negatively modulates fruit size by directly repressing PavKLUH expression

For sweet cherry, fruit size is one of the main targets in breeding programs owing to the high market value of larger fruits. KLUH/CYP78A5 is an important regulator of seed/fruit size in several plant species, but its molecular mechanism is largely unknown. In this study, we characterized the function of PavKLUH in the regulation of sweet cherry fruit size. The ectopic overexpression of PavKLUH in Arabidopsis increased the size of its siliques and seeds, whereas virus-induced gene silencing of PavKLUH in sweet cherry significantly decreased fruit size by restricting mesocarp cell expansion. We screened out an AP2/ERF transcription factor containing a B3-like domain, designated as PavRAV2, which was able to physically interact with PavKLUH promoter in a yeast one-hybrid (Y1H) system. In Y1H assays, electrophoretic mobility shift assays, and dual-luciferase reporter analyses, PavRAV2 directly bound to the promoter of PavKLUH in vitro and in vivo, and suppressed PavKLUH expression. Silencing of PavRAV2 resulted in enlarged fruit as a result of enhanced mesocarp cell expansion. Together, our results provide new insights into signaling pathways related to fruit size, and outline a possible mechanism for how the RAV transcription factor directly regulates CYP78A family members to influence fruit size and development.

Enhancing the Biological Control of Mite Species Infesting Olive Trees through Application of Predatory Mite Agistemus exsertus Gonzalez (Acari: Stigmaeidae) and Eco-Friendly Natural Compounds

Olive (Olea europaea L.) is a subtropical tree cultivated in arid, dry and temperate regions. Olive orchards in Al-Jouf of Saudi Arabia are the largest worldwide and currently face harmful pest infestation. The present study aimed at evaluating the efficiency of the predatory mite Agistemus exsertus Gonzalez (Acari: Stigmaeidae) and the exogenously applied melatonin (MT), glycine betaine (GB) and 5-aminolevulinic acid (ALA) as eco-friendly approaches for enhancing the biological control of four mite species (Tegolophus hassani, Oxycenus niloticus, Aceria olivi and Tetranychus urticae) infesting olive trees in Al-Jouf under laboratory and field conditions. Field experiment was conducted on 6-year-old Manzanillo olive trees grown in a private orchard farm in Al-Jouf during two seasons, 2020 and 2021. Results revealed that A. exsertus developed successfully from egg to adult. The females of T. hassani, O. niloticus, A. olivi, and T. urticae required 7.36, 8.89, 9.98 and 8.38 days, respectively, to develop from egg to adult at 28°C and 65 ± 5% relative humidity. O. niloticus was the most preferred prey of A. exsertus. The net reproductive rate (R0 ) was 42.1, 38.7, 34.6 and 36.8 females/female/generation, the intrinsic rate of increase (rm ) was 0.27, 0.26, 0.23 and 0.20 females/female/day, and the mean generation time (T) was 16.2, 17.1, 18.6 and 17.2 days when a predator consumed T. hassani, O. niloticus, A. olivi and T. urticae, respectively. The adult female consumed daily about 114 O. niloticus, 105 A. olivi, 95 T. hassani and 15.2 T. urticae individuals, respectively. A. exsertus proved to be an effective biocontrol agent against mites infesting olive trees. In addition, the exogenous application of 1 mM MT, 15 mM GB and 25 mg/L ALA, alone or in combination, caused significant mortality for the four mites. Application of these natural compounds, alone or in combination, also significantly enhanced the growth, relative water content, relative chlorophyll, content of flavonoid and nutrients, antioxidant enzymes activities, stress-related genes expression and fruit yield and quality of the infested olive trees compared to non-treated infested trees. This study is the first that demonstrates the efficiency of these eco-friendly approaches for controlling mites infesting olive trees, and could be used as a replacement for the harmful chemical acaricides.

Superoxide dismutase gene family in cassava revealed their involvement in environmental stress via genome-wide analysis

Superoxide dismutase (SOD) is a crucial metal-containing enzyme that plays a vital role in catalyzing the dismutation of superoxide anions, converting them into molecular oxygen and hydrogen peroxide, essential for enhancing plant stress tolerance. We identified 8 SOD genes (4 CSODs, 2 FSODs, and 2 MSODs) in cassava. Bioinformatics analyses provided insights into chromosomal location, phylogenetic relationships, gene structure, conserved motifs, and gene ontology annotations. MeSOD genes were classified into two groups through phylogenetic analysis, revealing evolutionary connections. Promoters of these genes harbored stress-related cis-elements. Duplication analysis indicated the functional significance of MeCSOD2/MeCSOD4 and MeMSOD1/MeMSOD2. Through qRT-PCR, MeCSOD2 responded to salt stress, MeMSOD2 to drought, and cassava bacterial blight. Silencing MeMSOD2 increased XpmCHN11 virulence, indicating MeMSOD2 is essential for cassava's defense against XpmCHN11 infection. These findings enhance our understanding of the SOD gene family's role in cassava and contribute to strategies for stress tolerance improvement.

Understanding the mechanism of red light-induced melatonin biosynthesis facilitates the engineering of melatonin-enriched tomatoes

Melatonin is a functionally conserved broad-spectrum physiological regulator found in most biological organisms in nature. Enrichment of tomato fruit with melatonin not only enhances its agronomic traits but also provides extra health benefits. In this study, we elucidate the full melatonin biosynthesis pathway in tomato fruit by identifying biosynthesis-related genes that encode caffeic acid O-methyltransferase 2 (SlCOMT2) and N-acetyl-5-hydroxytryptamine-methyltransferases 5/7 (SlASMT5/7). We further reveal that red light supplementation significantly enhances the melatonin content in tomato fruit. This induction relies on the "serotonin-N-acetylserotonin-melatonin" biosynthesis route via the SlphyB2-SlPIF4-SlCOMT2 module. Based on the regulatory mechanism, we design a gene-editing strategy to target the binding motif of SlPIF4 in the promoter of SlCOMT2, which significantly enhances the production of melatonin in tomato fruit. Our study provides a good example of how the understanding of plant metabolic pathways responding to environmental factors can guide the engineering of health-promoting foods.

Melatonin enhances drought tolerance by affecting jasmonic acid and lignin biosynthesis in wheat (Triticum aestivum L.)

Drought severely affects the yield of wheat (Triticum aestivum L.), which is mainly grown in arid and semi-arid regions. Melatonin plays an important role in various types of stress resistance in plants, including drought resistance. However, the molecular mechanism through which melatonin affects drought tolerance remains largely unknown. In this study, we revealed that melatonin (100 μM) significantly improved drought resistance during the maturation stage of Chinese Spring, Shi4185, and Hanxuan10 varieties, but not Chang6878. Further physiological, transcriptomic, and proteomic data analysis at the wheat seedling stage revealed that melatonin increased jasmonic acid (JA) content, upregulating the expression of JA genes (LOX1.5 and LOX2.1) and two transcription factors (HY5 and MYB86) under drought conditions. It also upregulated genes related to lignin biosynthesis (4CL2, P5CS1, and CCR2) as well as starch and sucrose metabolism (PME53 and SUS4). Additionally, melatonin alleviated photosynthetic and cell membrane damage caused by drought stress through maintaining low levels of hydrogen peroxide. The current results elucidate melatonin-regulated pathways in wheat and provide evidence for using melatonin as a potential biostimulant to improve wheat drought resistance under field conditions in the future.

Melatonin: A promising candidate for maintaining food security under the threat of phytopathogens

Plant immune response is tightly controlled by an interplay of various phytohormones and plant growth regulators. Among them, the role of salicylic acid, jasmonic acid, and ethylene is well established while some others such as nitric oxide, polyamines, and hydrogen sulfide have appeared to be key regulators of plant immunity. In addition, some other chemicals, such as melatonin (N-acetyl-5-methoxytryptamine), are apparently turning out to be the novel regulators of plant defense responses. Melatonin has shown promising results in enhancing resistance of plants to a variety of pathogens including fungi, bacteria, and viruses, however, the molecular mechanism of melatonin-mediated plant immune regulation is currently elusive. Evidence gathered so far indicates that melatonin regulates plant immunity by (1) facilitating the maintenance of ROS homeostasis, (2) interacting with other phytohormones and growth regulators, and (3) inducing the accumulation of defense molecules. Therefore, engineering crops with improved melatonin production could enhance crop productivity under stress conditions. This review extends our understanding of the multifaceted role of melatonin in the regulation of plant defense response and presents a putative pathway of melatonin functioning and its interaction with phytohormones during biotic stress.

Melatonin as mitochondria-targeted drug

Oxidative damage is associated to numerous diseases as well as aging development. Mitochondria found in most eukaryotic organisms to create the energy of the cell, generate free radicals during its action and they are chief targets of the oxidants. Mitochondrial activities outspread outside the borders of the cell and effect human physiology by modulating interactions among cells and tissues. Therefore, it has been implicated in several human disorders and conditions. Melatonin (MLT) is an endogenously created indole derivative that modifies several tasks, involving mitochondria-associated activities. These possessions make MLT a powerful defender against a selection of free radical-linked disorders. MLT lessens mitochondrial anomalies causing from extreme oxidative stress and may improve mitochondrial physiology. It is a potent and inducible antioxidant for mitochondria. MLT is produced in mitochondria of conceivably of all cells and it also appears to be a mitochondria directed antioxidant which has related defensive properties as the synthesized antioxidant molecules. This chapter summarizes the suggestion that MLT is produced in mitochondria as well as disorders of mitochondrial MLT production that may associate to a number of mitochondria-linked diseases. MLT as a mitochondria-targeted drug is also discussed.

Genetic and evolutionary dissection of melatonin response signaling facilitates the regulation of plant growth and stress responses

The expansion of gene families during evolution could generate functional diversity among their members to regulate plant growth and development. Melatonin, a phylogenetically ancient molecule, is vital for many aspects of a plant's life. Understanding the functional diversity of the molecular players involved in melatonin biosynthesis, signaling, and metabolism will facilitate the regulation of plant phenotypes. However, the molecular mechanism of melatonin response signaling elements in regulating this network still has many challenges. Here, we provide an in-depth analysis of the functional diversity and evolution of molecular components in melatonin signaling pathway. Genetic analysis of multiple mutants in plant species will shed light on the role of gene families in melatonin regulatory pathways. Phylogenetic analysis of these genes was performed, which will facilitate the identification of melatonin-related genes for future study. Based on the abovementioned signal networks, the mechanism of these genes was summarized to provide reference for studying the regulatory mechanism of melatonin in plant phenotypes. We hope that this work will facilitate melatonin research in higher plants and finely tuned spatio-temporal regulation of melatonin signaling.

Comprehensive analysis of cucumber RAV family genes and functional characterization of CsRAV1 in salt and ABA tolerance in cucumber

The RAV (related to ABI3 and VP1) transcription factors are specific and exist in plants, which contain a B3 DNA binding domain and/or an APETALA2 (AP2) DNA binding domain. RAVs have been extensively studied in plants, and more and more evidences show that RAVs are involved in various aspects of plant growth and development, stress resistance and hormone signal transduction. However, the systematic analysis of RAV family in cucumber is rarely reported. In this study, eight CsRAV genes were identified in cucumber genome and we further comprehensively analyzed their protein physicochemical properties, conserved domains, gene structure and phylogenetic relationships. The synteny analysis and gene duplications of CsRAV genes were also analysed. Cis-element analysis revealed that the CsRAVs promoter contained several elements related to plant hormones and abiotic stress. Expression analysis showed that NaCl and ABA could significantly induce CsRAV genes expression. Subcellular localization revealed that all CsRAVs were localized in the nucleus. In addition, 35S:CsRAV1 transgenic Arabidopsis and cucumber seedlings enhanced NaCl and ABA tolerance, revealing CsRAV1 may be an important regulator of abiotic stress response. In conclusion, comprehensive analysis of CsRAVs would provide certain reference for understanding the evolution and function of the CsRAV genes.

Functions of Melatonin during Postharvest of Horticultural Crops

Melatonin, a tryptophan-derived molecule, is endogenously generated in animal, plant, fungal and prokaryotic cells. Given its antioxidant properties, it is involved in a myriad of signaling functions associated with various aspects of plant growth and development. In higher plants, melatonin (Mel) interacts with plant regulators such as phytohormones, as well as reactive oxygen and nitrogen species including hydrogen peroxide (H2O2), nitric oxide (NO) and hydrogen sulfide (H2S). It shows great potential as a biotechnological tool to alleviate biotic and abiotic stress, to delay senescence and to conserve the sensory and nutritional quality of postharvest horticultural products which are of considerable economic importance worldwide. This review provides a comprehensive overview of the biochemistry of Mel, whose endogenous induction and exogenous application can play an important biotechnological role in enhancing the marketability and hence earnings from postharvest horticultural crops.

Exogenously applied melatonin alleviates the damage in cucumber plants caused by Aphis goosypii through altering the insect behavior and inducing host plant resistance

BACKGROUND

Aphis gossypii Glover is the main pest found in most cucumber-producing areas. Melatonin (MT) has been widely studied in protecting plants from environmental stresses and pathogens. However, little knowledge is available on the impact of MT on insect resistance.

RESULTS

The fecundity of aphids on MT-treated cucumber leaves was inhibited. Interestingly, MT-treated plants were more attractive to aphids, which would prevent the large-scale transmission of viruses caused by the random movement of aphids. Meanwhile, MT caused varying degrees of change in enzyme activities related to methylesterified HG degradation, antioxidants, defense systems and membrane lipid peroxidation. Furthermore, transcriptomic analysis showed that MT induced 2360 differentially expressed genes (DEGs) compared with the control before aphid infection. These DEGs mainly were enriched in hormone signal transduction, MAPK signaling pathway, and plant-pathogen interaction, revealing that MT can help plants acquire inducible resistance and enhance plant immunity. Subsequently, 2397 DEGs were identified after aphid infection. Further analysis showed that MT-treated plants possessed stronger JA signal, reactive oxygen species stability, and the ability of flavonoid synthesis under aphid infection, while mediating plant growth and sucrose metabolism.

CONCLUSION

In summary, MT as an environmentally friendly substance mitigated aphid damage to cucumbers by affecting the aphids themselves and enhancing plant resistance. This will facilitate exploring sustainable MT-based strategies for cucumber aphid control. © 2022 Society of Chemical Industry.

CDK1 serves as a therapeutic target of adrenocortical carcinoma via regulating epithelial-mesenchymal transition, G2/M phase transition, and PANoptosis

Background

Adrenocortical carcinoma (ACC) is an extremely rare, aggressive tumor with few effective therapeutic options or drugs. Mitotane (Mtn), which is the only authorized therapeutic drug, came out in 1970 and is still the only first-line treatment for ACC in spite of serious adverse reaction and a high recurrence rate.

Methods

By in silico analysis of the ACC dataset in the cancer genome atlas (TCGA), we determined that high expression levels of cyclin-dependent kinase-1 (CDK1) were significantly related to the adverse clinical outcomes of ACC. In vitro and in vivo experiments were performed to evaluate the role of CDK1 in ACC progression through gain and loss of function assays in ACC cells. CDK1 inhibitors were screened to identify potential candidates for the treatment of ACC. RNA sequencing, co-immunoprecipitation, and immunofluorescence assays were used to elucidate the mechanism.

Results

Overexpression of CDK1 in ACC cell lines promoted proliferation and induced the epithelial-to-mesenchymal transition (EMT), whereas knockdown of CDK1 expression inhibited growth of ACC cell lines. The CDK1 inhibitor, cucurbitacin E (CurE), had the best inhibitory effect with good time-and dose-dependent activity both in vitro and in vivo. CurE had a greater inhibitory effect on ACC xenografts in nude mice than mitotane, without obvious adverse effects. Most importantly, combined treatment with CurE and mitotane almost totally eliminated ACC tumors. With respect to mechanism, CDK1 facilitated the EMT of ACC cells via Slug and Twist and locked ACC cells into the G2/M checkpoint through interaction with UBE2C and AURKA/B. CDK1 also regulated pyroptosis, apoptosis, and necroptosis (PANoptosis) of ACC cells through binding with the PANoptosome in a ZBP1-dependent way.

Conclusions

CDK1 could be exploited as an essential therapeutic target of ACC via regulating the EMT, the G2/M checkpoint, and PANoptosis. Thus, CurE may be a potential candidate drug for ACC therapy with good safety and efficacy, which will meet the great need of patients with ACC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03641-y.

Melatonin biosynthesis and signal transduction in plants in response to environmental conditions

Melatonin, the most widely distributed hormone in nature, plays important roles in plants. Many physiological processes in plants are linked to melatonin, including seed germination, anisotropic cell growth, and senescence. Compared with animals, different plants possess diverse melatonin biosynthetic pathways and regulatory networks. Whereas melatonin biosynthesis in animals is known to be regulated by ambient signals, little is known about how melatonin biosynthesis in plants responds to environmental signals. Plants are affected by numerous environmental factors, such as light, temperature, moisture, carbon dioxide, soil conditions, and nutrient availability at all stages of development and in different tissues. Melatonin content exhibits dynamic changes that affect plant growth and development. Melatonin plays various species-specific roles in plant responses to different environmental conditions. However, much remains to be learned, as not all environmental factors have been studied, and little is known about the mechanisms by which these factors influence melatonin biosynthesis. In this review, we provide a detailed, systematic description of melatonin biosynthesis and signaling and of the roles of melatonin in plant responses to different environmental factors, providing a reference for in-depth research on this important issue.

Anabolism and signaling pathways of phytomelatonin

Phytomelatonin is a small multifunctional molecule found ubiquitously in plants, which plays an important role in plant growth, development, and biotic and abiotic stress responses. The classical biosynthetic and metabolic pathways of phytomelatonin have been elucidated, and uncovering alternative pathways has deepened our understanding of phytomelatonin synthesis. Phytomelatonin functions mainly via two pathways. In the direct pathway, phytomelatonin mediates the stress-induced reactive oxygen species burst through its strong antioxidant capacity. In the indirect pathway, phytomelatonin acts as a signal to activate signaling cascades and crosstalk with other plant hormones. The phytomelatonin receptor PMTR1/CAND2 was discovered in 2018, which enhanced our understanding of phytomelatonin function. This review summarizes the classical and potential pathways involved in phytomelatonin synthesis and metabolism. To elucidate the functions of phytomelatonin, we focus on the crosstalk between phytomelatonin and other phytohormones. We propose two models to explain how PMTR1 transmits the phytomelatonin signal through the G protein and MAPK cascade. This review will facilitate the identification of additional signaling molecules that function downstream of the phytomelatonin signaling pathway, thus improving our understanding of phytomelatonin signal transmission.

Phytomelatonin as a central molecule in plant disease resistance

Melatonin is an essential phytohormone in the regulation of many plant processes, including during plant development and in response to stress. Pathogen infections cause serious damage to plants and reduce agricultural production. Recent studies indicate that melatonin plays important roles in alleviating bacterial, fungal, and viral diseases in plants and post-harvest fruits. Herein, we summarize information related to the effects of melatonin on plant disease resistance. Melatonin, reactive oxygen species, and reactive nitrogen species form a complex loop in plant-pathogen interaction to regulate plant disease resistance. Moreover, crosstalk of melatonin with other phytohormones including salicylic acid, jasmonic acid, auxin, and abscisic acid further activates plant defense genes. Melatonin plays an important role not only in plant immunity but also in alleviating pathogenicity. We also summarize the known processes by which melatonin mediates pathogenicity via negatively regulating the expression levels of genes related to cell viability as well as virulence-related genes. The multiple mechanisms underlying melatonin influences on both plant immunity and pathogenicity support the recognition of the essential nature of melatonin in plant-pathogen interactions, highlighting phytomelatonin as a critical molecule in plant immune responses.

Genome-Wide Analysis of the RAV Gene Family in Wheat and Functional Identification of TaRAV1 in Salt Stress

RAV transcription factors (TFs) are unique to higher plants and contain both B3 and APETALA2 (AP2) DNA binding domains. Although sets of RAV genes have been identified from several species, little is known about this family in wheat. In this study, 26 RAV genes were identified in the wheat genome. These wheat RAV TFs were phylogenetically clustered into three classes based on their amino acid sequences. A TaRAV gene located on chromosome 1D was cloned and named TaRAV1. TaRAV1 was expressed in roots, stems, leaves, and inflorescences, and its expression was up-regulated by heat while down-regulated by salt, ABA, and GA. Subcellular localization analysis revealed that the TaRAV1 protein was localized in the nucleus. The TaRAV1 protein showed DNA binding activity in the EMSA assay and transcriptional activation activity in yeast cells. Overexpressing TaRAV1 enhanced the salt tolerance of Arabidopsis and upregulated the expression of SOS genes and other stress response genes. Collectively, our data suggest that TaRAV1 functions as a transcription factor and is involved in the salt stress response by regulating gene expression in the SOS pathway.

PP2C1 fine-tunes melatonin biosynthesis and phytomelatonin receptor PMTR1 binding to melatonin in cassava

Melatonin is an important molecule in both animals and plants, regulating circadian rhythms and stress responses. Therefore, the improvement of melatonin accumulation not only strengthens the function of melatonin but also improves stress resistance in crops. Although melatonin biosynthetic enzymes have been identified through reverse genetics previously, an investigation of melatonin level-related genes through forward genetics in plants has yet to be performed. In this study, a genome-wide association study using cassava natural population of 298 genetic resources identified melatonin accumulation 1 (MA1), which regulates the natural variation of melatonin levels in cassava. We found that MA1 encodes type 2C protein phosphatase 1 (PP2C1), which serves as a negative regulator of melatonin levels in cassava. MePP2C1 physically interacts with MeRAV1/2 and MeWRKY20 and dephosphorylates them at serine (S) 35 residue, S34 residue, and S176 residue, respectively, thereby hindering their transcriptional activation on downstream melatonin biosynthetic genes. Notably, MePP2C1 interacts with phytomelatonin receptor MePMTR1 and dephosphorylates it at S11 residue, repressing its binding to melatonin. In summary, this study demonstrates that MePP2C1 as MA1 plays dual roles in negatively regulating both melatonin accumulation and signaling, extending the understanding of the molecular mechanism underlying melatonin accumulation and signaling through forward genetics in plants.

Variation in Melatonin Contents and Genetic Dissection of Melatonin Biosynthesis in Sesame

In recent years, people have become increasingly interested in bioactive molecules in plants that are beneficial to human health, and melatonin (N-acetyl-5-methoxytryptamine) has attracted research attention due to its excellent performance. In this study, the content of melatonin in oilseeds was investigated. From the results, it was found that sesame is an important natural food source of melatonin intake. Furthermore, the variation in melatonin content was explored in a natural sesame population, and its contents varied from 0.04 to 298.62 ng g^-1. Through a genome-wide association study (GWAS), a candidate gene SiWRKY67 was screened that regulates melatonin content in sesame. The sesame hairy root transformation system was developed and used to verify this gene, and it was found that the overexpression of SiWRKY67 could positively promote the melatonin content in the hairy roots. Our results provide not only a foundation for understanding the genetic structure of melatonin content in sesame seeds but also a reference for the marker-assisted breeding of sesame varieties with high melatonin content.

Insight into melatonin-mediated response and signaling in the regulation of plant defense under biotic stress

Melatonin plays a crucial role in the mitigation of plant biotic stress through induced defense responses and pathogen attenuation. Utilizing the current knowledge of signaling and associated mechanism of this phytoprotectant will be invaluable in sustainable plant disease management. Biotic stress in plants involves complex regulatory networks of various sensory and signaling molecules. In this context, the polyfunctional, ubiquitous-signaling molecule melatonin has shown a regulatory role in biotic stress mitigation in plants. The present review conceptualized the current knowledge concerning the melatonin-mediated activation of the defense signaling network that leads to the resistant or tolerant phenotype of the infected plants. Fundamentals of signaling networks involved in melatonin-induced reactive oxygen species (ROS) or reactive nitrogen species (RNS) scavenging through enzymatic and non-enzymatic antioxidants have also been discussed. Increasing evidence has suggested that melatonin acts upstream of mitogen-activated proteinase kinases in activation of defense-related genes and heat shock proteins that provide immunity against pathogen attack. Besides, the direct application of melatonin on virulent fungi and bacteria showed disrupted spore morphology, destabilization of cell ultrastructure, reduced biofilm formation, and enhanced mortality that led to attenuate disease symptoms on melatonin-treated plants. The transcriptome analysis has revealed the down-regulation of pathogenicity genes, metabolism-related genes, and up-regulation of fungicide susceptibility genes in melatonin-treated pathogens. The activation of melatonin-mediated systemic acquired resistance (SAR) through cross-talk with salicylic acid (SA), jasmonic acid (JA) has been essential for viral disease management. The high endogenous melatonin concentration has also been correlated with the up-regulation of genes involved in pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity (ETI). The present review highlights the versatile functions of melatonin towards direct inhibition of pathogen propagule along with active participation in mediating oxidative burst and simulating PTI, ETI and SAR responses. The hormonal cross-talk involving melatonin mediated biotic stress tolerance through defense signaling network suggests its suitability in a sustainable plant protection system.

Transcriptome Analysis Reveals that Exogenous Melatonin Confers Lilium Disease Resistance to Botrytis elliptica

Leaf blight, caused by Botrytis elliptica (Berk.) Cooke, is a devastating disease that limits the production of Lilium in China and in other countries worldwide. Numerous studies have indicated that plants have evolved sophisticated and effective signal transduction and defense-related pathways in response to pathogen invasion. Recently, particular attention has been given to the action(s) of melatonin in plants in response to biotic stress, and the role of melatonin in plant–pathogen interactions has also been discussed. In this study, RNA-seq was applied to analyze the transcriptomic changes in Lilium leaves that were pre-treated and post-treated with melatonin after B. elliptica infection for 0, 12, 24, 36, and 72 h and then compare those changes with those of the control. Treatment with exogenous melatonin and infection with B. elliptica caused differential expression of a large number of genes in Lilium leaves. KEGG pathway analysis showed that, after melatonin treatment, the defense-related DEGs were mainly enriched in plant–pathogen interactions, plant hormone signal transduction, MAPK signaling pathways, phenylpropanoid biosynthesis, and phenylalanine metabolism. RT–qPCR was used to verify the expression changes of 12 DEGs, the results of which were consistent with the RNA-seq analysis results. The expression of DEGs related to the MAPK pathway were significantly different between the MB group and the HB group, suggesting that, via the MAPK signaling cascade, melatonin may play a role in the disease resistance of Lilium to B. elliptica. This study provides a new perspective and information for molecular-based breeding of Lilium disease resistance.

Exogenous Melatonin Improves Pear Resistance to Botryosphaeria dothidea by Increasing Autophagic Activity and Sugar/Organic Acid Levels

Pear is an important fruit tree worldwide, but it is often infected by the pathogen Botryosphaeria dothidea, which causes pear ring rot disease. To explore the effect of exogenous melatonin on the disease resistance of pear, we treated inoculated pear fruits with different concentrations of melatonin. The results showed that 100 μΜ of melatonin had the most significant effect with resistance to B. dothidea. In addition, melatonin treatment significantly reduced the diameter of disease lesions and enhanced the endogenous melatonin content in pears inoculated with B. dothidea. Compared with the control treatment, melatonin treatment suppressed increases in reactive oxygen species (ROS) and activated ROS-scavenging enzymes. Treatment with exogenous melatonin maintained ascorbic acid-glutathione at more reductive status. The expression levels of core autophagic genes and autophagosome formation were elevated by melatonin treatment in pear fruits. Silencing of PbrATG5 in Pyrus pyrifolia conferred sensitivity to inoculation that was only slightly attenuated by melatonin treatment. After inoculation with B. dothidea, exogenous melatonin treatment led to higher levels of soluble sugars and organic acids in pear fruits than H₂O treatment. Overall, our results demonstrate that melatonin enhances resistance to B. dothidea by increasing autophagic activity and soluble sugar/organic acid accumulation.

NF-κB/ABCA1 pathway aggravates ox-LDL-induced cell pyroptosis by activation of NLRP3 inflammasomes in THP-1-derived macrophages

OBJECTIVE

NF-κB (nuclear transcription factor-kappa B) plays a well-known function in the regulation of immune responses and inflammation, but growing evidences support a major role of it in atherosclerosis. Currently, the regulatory mechanism of NF-κB pathway involved in atherosclerosis remains unclear.

METHODS

To investigate the role of ox-LDL (oxidized low-density lipoprotein) in NF-κB regulation, the protein expression of phosphorylated NF-κB, a marker of NF-κB pathway activation was measured. The pyroptosis of macrophage was evaluated by western blot and fluorescence microscope. Cholesterol efflux capacity was determined by fluorescence assay and oil red O staining. The inhibitor of activation of NF-κB signal was used to assess the effect of NF-κB signal on macrophage pyroptosis and cholesterol efflux in macrophage. Small interfering RNA of ABCA1 (cholesterol transporters ATP binding boxes A1) was used to assess the effect of ABCA1 on macrophage pyroptosis.

RESULTS

In this study, we reported THP-1 derived macrophage can be stimulated to increase pyroptosis by ox-LDL in a concentration-dependent manner. Macrophage pyroptosis was correlated with enhanced activation of NF-κB signal. After using inhibitor of NF-κB phosphorylation to attenuate activation of NF-κB signal, we identified and confirmed the decrease of macrophage pyroptosis and the occurrence of ox-LDL-induced cholesterol efflux disorder. Furthermore, we found that the downregulation of ABCA1 led to increased cell inflammation death. But pyroptosis was blocked, may led to cholesterol efflux dysfunction.

CONCLUSION

Taken together, the present results indicate that the mechanism of NF-κB involved in the development of atherosclerosis depends on mediating cell pyroptosis and cholesterol efflux and provide significant light on macrophage NF-κB signal in atherosclerosis.

The co-modulation of RAV transcription factors in ROS burst and extensive transcriptional reprogramming underlies disease resistance in cassava

MeRAVs positively regulate ROS burst and the expression of downstream disease resistance-related genes, which underlie improved disease resistance to Xam. Cassava (Manihot esculenta Crantz) is an important food crop and energy crop, but its yield is seriously affected by cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis (Xam). Related to ABI3/VP1 (RAV) transcription factor family belongs to the APETALA2/Ethylene-Responsive Factor (AP2/ERF) family, which plays an important role in plant growth, development and response to biotic and abiotic stresses. In this study, we found that MeRAVs positively co-regulates the resistance to Xam and stimulates the innate immune response by regulating reactive oxygen species (ROS) burst in cassava. Dual-luciferase assay showed that seven MeRAVs exhibited transcriptional activate activity by binding CAACA motif and CACCTG motif. A large number of differentially expressed genes (DEGs) were identified through RNA-seq analysis of MeRAVs-silenced lines, and the DEGs co-regulated by seven MeRAVs accounted for more than 45% of the total DEGs. In addition, seven MeRAVs positively regulate expression of disease resistance-related genes through directly binding to their promoters. In summary, MeRAVs co-regulate ROS burst and the expression of downstream disease resistance-related genes, which underlie improved disease resistance to Xam.

Exogenous melatonin improves the resistance to cucumber bacterial angular leaf spot caused by Pseudomonas syringae pv. Lachrymans

Pseudomonas syringae pv. Lachrymans (Psl) is a bacterial pathogen that causes cucumber bacterial angular leaf spot (BALS). It is known that melatonin (MT), as a pleiotropic signal molecule, can improve plant stress tolerance, but less information is available about the function of MT on plant resistance to bacteria disease. Here, we investigated the effect of MT on cucumber BALS. Our results show that MT inhibited the bacteria Psl growth significantly in vitro and attenuated cucumber BALS remarkably in vivo. The concentration of bacteria in leaves treated with 0.1 mM MT was approximately 10,000 times reduced at 5 days-post-inoculation (dpi), compared to the control without MT. Transcriptomic analysis showed that 225 differentially expressed genes (DEGs) were induced in leaves after just MT treatment for 3 h. The functions of these DEGs were mainly associated with hormone signal transduction, mitogen-activated protein kinase (MAPK) signaling pathway, and photosynthesis, suggesting that MT could regulate plant growth and induce plant immunity. Moreover, 665 DEGs were induced when leaves were treated with exogenous MT in combination with the bacteria inoculation for 12 h. The functions of these DEGs were much related to plant-pathogen interaction, hormone signal transduction, and amino acids biosynthesis pathways. Many MT-induced DEGs were involved in some distinct signal transduction pathways, such as calmodulin (CaM), polyamines (PAs), nitric oxide (NO), and salicylic acid (SA). The physiological analysis shows that exogenous MT spray reduced the stomatal aperture and enhanced the activities of antioxidant and defense enzymes, which were in consistent with the results of the transcriptome analysis. In addition, MT may function in regulating the metabolic balance between plant growth and defense. In conclusion, our results demonstrate that MT could alleviate the cucumber BALS via inhibiting propagation and invasion of Psl, activating plant signaling, enhancing antioxidative and defense systems, inducing stress-related genes expression, and regulating the plant growth-defense balance.

Fine-tuning of pathogenesis-related protein 1 (PR1) activity by the melatonin biosynthetic enzyme ASMT2 in defense response to cassava bacterial blight

Melatonin is widely involved in plant disease resistance through modulation of immune responses. Pathogenesis-related (PR) proteins play important roles in plant immune responses. However, the direct association between melatonin biosynthetic enzyme and PR protein remains elusive in plants. In this study, we found that N-acetylserotonin O-methyltransferase 2 (MeASMT2) physically interacted with MePR1 in vitro and in vivo, thereby promoting the anti-bacterial activity of MePR1 against Xanthomonas axonopodis pv. manihotis (Xam). Consistently, MeASMT2 improved the effect of MePR1 on positively regulating cassava disease resistance. In addition, we found that type 2C protein phosphatase 1 (MePP2C1) interacted with MeASMT2 to interfere with MePR1-MeASMT2 interaction, so as to inhibiting the effect of MeASMT2 and MePR1 on positively regulating cassava disease resistance. In contrast to the increased transcripts of MeASMT2 and MePR1 in response to Xam infection, the transcript of MePP2C1 was decreased upon Xam infection. Therefore, disease activated MeASMT2 was released from disease inhibited MePP2C1, so as to improving the anti-bacterial activity of MePR1, resulting in improved immune response. In summary, this study illustrates the dynamic modulation of the MePP2C1-MeASMT2-MePR1 module on cassava defense response against cassava bacterial blight (CBB), extending the understanding of the correlation between melatonin biosynthetic enzyme and PR in plants.

Functional roles of the birch BpRAV1 transcription factor in salt and osmotic stress response

RAV (Related to ABI3/VP1) transcription factors play vital roles in regulating plant response to abiotic stresses; however, the regulatory mechanisms underlying stress response are still poorly understood for most of the RAVgenes. In this study, a novel gene BpRAV1 was cloned from white birch (Betula platyphylla). BpRAV1 protein is localized in the nucleus and serves as a transcriptional activator. The expression of BpRAV1 was induced by salt and osmotic stress treatments. BpRAV1-overexpression birch seedlings exhibited dramatically less ROS accumulation and reduced cell death in response to salt and osmotic stresses. BpRAV1 can specifically bind to the known RAV1A element. In addition, a novel cis-acting element (termed RBS1) bound by BpRAV1 was identified by transcription factor (TF)- centered Y1H assay. BpRAV1 activated the RAV1A and RBS1 elements to induce the expression of SOD and POD genes, resulting in increased SOD and POD activities to enhance ROS scavenging ability, thus improving salt and osmotic stress tolerance. These results indicate that BpRAV1 is a positive regulator governing abiotic stress response.

Phosphorylation of RAV1/2 by KIN10 is essential for transcriptional activation of CAT6/7, which underlies oxidative stress response in cassava

Related to ABI3/VP1 (RAV) transcription factors have important roles in plant stress responses; however, it is unclear whether RAVs regulates oxidative stress response in cassava (Manihot esculenta). In this study, we report that MeRAV1/2 positively regulate oxidative stress resistance and catalase (CAT) activity in cassava. Consistently, RNA sequencing (RNA-seq) identifies three MeCATs that are differentially expressed in MeRAV1/2-silenced cassava leaves. Interestingly, MeCAT6 and MeCAT7 are identified as direct transcriptional targets of MeRAV1/2 via binding to their promoters. In addition, protein kinase MeKIN10 directly interacts with MeRAV1/2 to phosphorylate them at Ser45 and Ser44 residues, respectively, to promote their direct transcriptional activation on MeCAT6 and MeCAT7. Site mutation of MeRAV1S45A or MeRAV2S44A has no significant effect on the activities of MeCAT6 and MeCAT7 promoters or on oxidative stress resistance. In summary, this study demonstrates that the phosphorylation of MeRAV1/2 by MeKIN10 is essential for its direct transcriptional activation of MeCAT6/7 in response to oxidative stress.

Cassava diseases caused by Xanthomonas phaseoli pv. manihotis and Xanthomonas cassavae

Xanthomonas phaseoli pv. manihotis (Xpm) and X. cassavae (Xc) are two bacterial pathogens attacking cassava. Cassava bacterial blight (CBB) is a systemic disease caused by Xpm, which might have dramatic effects on plant growth and crop production. Cassava bacterial necrosis is a nonvascular disease caused by Xc with foliar symptoms similar to CBB, but its impacts on the plant vigour and the crop are limited. In this review, we describe the epidemiology and ecology of the two pathogens, the impacts and management of the diseases, and the main research achievements for each pathosystem. Because Xc data are sparse, our main focus is on Xpm and CBB.

Genome-Wide Identification and Expression Analysis of AP2/ERF Transcription Factor Related to Drought Stress in Cultivated Peanut (Arachis hypogaea L.)

APETALA2/ethylene response element-binding factor (AP2/ERF) transcription factors (TFs) have been found to regulate plant growth and development and response to various abiotic stresses. However, detailed information of AP2/ERF genes in peanut against drought has not yet been performed. Herein, 185 AP2/ERF TF members were identified from the cultivated peanut (A. hypogaea cv. Tifrunner) genome, clustered into five subfamilies: AP2 (APETALA2), ERF (ethylene-responsive-element-binding), DREB (dehydration-responsive-element-binding), RAV (related to ABI3/VP), and Soloist (few unclassified factors)). Subsequently, the phylogenetic relationship, intron-exon structure, and chromosomal location of AhAP2/ERF were further characterized. All of these AhAP2/ERF genes were distributed unevenly across the 20 chromosomes, and 14 tandem and 85 segmental duplicated gene pairs were identified which originated from ancient duplication events. Gene evolution analysis showed that A. hypogaea cv. Tifrunner were separated 64.07 and 66.44 Mya from Medicago truncatula L. and Glycine max L., respectively. Promoter analysis discovered many cis-acting elements related to light, hormones, tissues, and stress responsiveness process. The protein interaction network predicted the exitance of functional interaction among families or subgroups. Expression profiles showed that genes from AP2, ERF, and dehydration-responsive-element-binding subfamilies were significantly upregulated under drought stress conditions. Our study laid a foundation and provided a panel of candidate AP2/ERF TFs for further functional validation to uplift breeding programs of drought-resistant peanut cultivars.

A Phytomelatonin-Rich Extract Obtained from Selected Herbs with Application as Plant Growth Regulator

The animal hormone melatonin (N-acetyl-5-methoxytryptamine) is a pleiotropic molecule with multiple and various functions. Phytomelatonin is the melatonin from plants and was discovered in 1995 in some species. Phytomelatonin is considered an interesting molecule in the physiology of plants, as it seems to be involved in many actions, such as germination, growth, rooting and parthenocarpy, including fruit set and ripening; it also seems to play a role during postharvest. It has been studied in processes such as primary and secondary metabolism, photosynthesis and senescence, as well as in the nitrogen and sulfur cycles. Phytomelatonin up- and down-regulates many relevant genes related to plant hormones and key genes related to the above-mentioned aspects. One of the most decisive aspects of phytomelatonin is its relevant role as a bioprotective and alleviating agent against both biotic and abiotic stressors, which has opened up the possibility of using melatonin as a phytoprotector and biostimulant in agriculture. In this respect, using material of plant origin to obtain extracts rich in phytomelatonin instead of using synthetic melatonin (thus avoiding unwanted by-products) has become a topic of discussion. This work characterized the phytomelatonin-rich extracts obtained from selected herbs and determined their contents of phytomelatonin, phenols and flavonoids; the antioxidant activity was also measured. Finally, two melatonin-specific bioassays in plants were applied to demonstrate the excellent biological properties of the natural phytomelatonin-rich extracts obtained. The herb composition and the protocols for obtaining the extracts rich in phytomelatonin are in the process of registration for their legal protection.