Indole-3 acetic acid negatively regulates rose black spot disease resistance through antagonizing the salicylic acid signaling pathway via jasmonic acid.

MAIN CONCLUSION: IAA cooperates with JA to inhibit SA and negatively regulates rose black spot disease resistance. Black spot disease caused by the fungus Marssonina rosae is the most prevalent and severe ailment in rose cultivation, leading to the appearance of black spots on leaves and eventual leaf fall, significantly impacting the utilization of roses in gardens. Salicylic acid (SA) and jasmonic acid (JA) are pivotal hormones that collaborate with indole-3 acetic acid (IAA) in regulating plant defense responses; however, the detailed mechanisms underlying the induction of black spot disease resistance by IAA, JA, and SA remain unclear. In this study, transcript analysis was conducted on resistant (R13-54) and susceptible (R12-26) lines following M. rosae infection. In addition, the impact of exogenous interference with IAA on SA- and JA-mediated disease resistance was examined. The continuous accumulation of JA, in synergy with IAA, inhibited activation of the SA signaling pathway in the early infection stage, thereby negatively regulating the induction of effective resistance to black spot disease. IAA administration alleviated the inhibition of SA on JA to negatively regulate the resistance of susceptible strains by further enhancing the synthesis and accumulation of JA. However, IAA did not contribute to the negative regulation of black spot resistance when high levels of JA were inhibited. Virus-induced gene silencing of RcTIFY10A, an inhibitor of the JA signaling pathway, further suggested that IAA upregulation led to a decrease in disease resistance, a phenomenon not observed when the JA signal was inhibited. Collectively, these findings indicate that the IAA-mediated negative regulation of black spot disease resistance relies on activation of the JA signaling pathway.

Lactic acid induced defense responses in tobacco against Phytophthora nicotianae.

Induced resistance is considered an eco-friendly disease control strategy, which can enhance plant disease resistance by inducing the plant's immune system to activate the defense response. In recent years, studies have shown that lactic acid can play a role in plant defense against biological stress; however, whether lactic acid can improve tobacco resistance to Phytophthora nicotianae, and its molecular mechanism remains unclear. In our study, the mycelial growth and sporangium production of P. nicotianae were inhibited by lactic acid in vitro in a dose-dependent manner. Application of lactic acid could reduce the disease index, and the contents of total phenol, salicylic acid (SA), jasmonic acid (JA), lignin and H2O2, catalase (CAT) and phenylalanine ammonia-lyase (PAL) activities were significantly increased. To explore this lactic acid-induced protective mechanism for tobacco disease resistance, RNA-Seq analysis was used. Lactic acid enhances tobacco disease resistance by activating Ca2+, reactive oxygen species (ROS) signal transduction, regulating antioxidant enzymes, SA, JA, abscisic acid (ABA) and indole-3-acetic acid (IAA) signaling pathways, and up-regulating flavonoid biosynthesis-related genes. This study demonstrated that lactic acid might play a role in inducing resistance to tobacco black shank disease; the mechanism by which lactic acid induces disease resistance includes direct antifungal activity and inducing the host to produce direct and primed defenses. In conclusion, this study provided a theoretical basis for lactic acid-induced resistance and a new perspective for preventing and treating tobacco black shank disease.

Genome-wide identification of ZmMYC2 binding sites and target genes in maize.

BACKGROUND: Jasmonate (JA) is the important phytohormone to regulate plant growth and adaption to stress signals. MYC2, an bHLH transcription factor, is the master regulator of JA signaling. Although MYC2 in maize has been identified, its function remains to be clarified. RESULTS: To understand the function and regulatory mechanism of MYC2 in maize, the joint analysis of DAP-seq and RNA-seq is conducted to identify the binding sites and target genes of ZmMYC2. A total of 3183 genes are detected both in DAP-seq and RNA-seq data, potentially as the directly regulating genes of ZmMYC2. These genes are involved in various biological processes including plant growth and stress response. Besides the classic cis-elements like the G-box and E-box that are bound by MYC2, some new motifs are also revealed to be recognized by ZmMYC2, such as nGCATGCAnn, AAAAAAAA, CACGTGCGTGCG. The binding sites of many ZmMYC2 regulating genes are identified by IGV-sRNA. CONCLUSIONS: All together, abundant target genes of ZmMYC2 are characterized with their binding sites, providing the basis to construct the regulatory network of ZmMYC2 and better understanding for JA signaling in maize.

[Characterization of sequences, expression profiling, and natural allelic variation analysis of the MYC gene family in sorghum (Sorghum bicolor)].

Sorghum aphid (Melanaphis sacchari) and head smut fungi (Sporisorium reilianum) infesting sorghum cause delayed growth and development, and reduce yield and quality. This study use bioinformatics and molecular biological approaches to profile the gene expression pattern during sorghum development and under pest infestation, and analyzed the natural allelic DNA variation of sorghum MYC gene family. The findings provide insights for potential application in breeding the stress resistant and high productivity sorghum varieties. The results indicated that there are 28 MYC genes identified in sorghum genome, distributed on 10 chromosomes. The bHLH_MYC_N and HLH domains are the conserved domains of the MYC gene in sorghum. Gene expression analysis showed that SbbHLH35.7g exhibited high expression levels in leaves, SbAbaIn showed strong expression in early grains, and SbMYC2.1g showed high expression levels in mature pollen. In anti-aphid strains at the 5-leaf stage, SbAbaIn, SbLHW.4g and SbLHW.2g were significantly induced in leaves, while SbbHLH35.7g displayed the highest expression level in panicle tissue, which was significantly induced by the infection of head smut. Promoter cis-element analysis identified methyl jasmonate (MJ), abscisic acid (ABA), salicylic acid (SA) and MYB-binding sites related to drought-stress inducibility. Furthermore, genomic resequencing data analysis revealed natural allelic DNA variations such as single nucleotide polymorphism (SNP) and insertion-deletion (INDEL) for the key SbMYCs. Protein interaction network analysis using STRING indicated that SbAbaIn interacts with TIFYdomain protein, and SbbHLH35.7g interacts with MDR and imporin. SbMYCs exhibited temporal and spatial expression patterns and played vital roles during the sorghum development. Infestation by sugarcane aphids and head smut fungi induced the expression of SbAbaIn and SbbHLH35.7g, respectively. SbAbaIn modulated the jasmonic acid (JA) pathway to regulate the expression of defensive genes, conferring resistance to insects. On the other hand, SbbHLH35.7g participated in detoxification reactions to defend against pathogens.

Jasmonic acid (JA)-mediating MYB transcription factor1, JMTF1, coordinates the balance between JA and auxin signalling in the rice defence response.

The plant hormone jasmonic acid (JA) is a signalling compound involved in the regulation of cellular defence and development in plants. In this study, we investigated the roles of a JA-responsive MYB transcription factor, JMTF1, in the JA-regulated defence response against rice bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo). JMTF1 did not interact with any JASMONATE ZIM-domain (JAZ) proteins. Transgenic rice plants overexpressing JMTF1 showed a JA-hypersensitive phenotype and enhanced resistance against Xoo. JMTF1 upregulated the expression of a peroxidase, OsPrx26, and monoterpene synthase, OsTPS24, which are involved in the biosynthesis of lignin and antibacterial monoterpene, γ-terpinene, respectively. OsPrx26 was mainly expressed in the vascular bundle. Transgenic rice plants overexpressing OsPrx26 showed enhanced resistance against Xoo. In addition to the JA-hypersensitive phenotype, the JMTF1-overexpressing rice plants showed a typical auxin-related phenotype. The leaf divergence and shoot gravitropic responses were defective, and the number of lateral roots decreased significantly in the JMTF1-overexpressing rice plants. JMTF1 downregulated the expression of auxin-responsive genes but upregulated the expression of OsIAA13, a suppressor of auxin signalling. The rice gain-of-function mutant Osiaa13 showed high resistance against Xoo. Transgenic rice plants overexpressing OsEXPA4, a JMTF1-downregulated auxin-responsive gene, showed increased susceptibility to Xoo. JMTF1 is selectively bound to the promoter of OsPrx26 in vivo. These results suggest that JMTF1 positively regulates disease resistance against Xoo by coordinating crosstalk between JA- and auxin-signalling in rice.

Natural variation in OsMYB8 confers diurnal floret opening time divergence between indica and japonica subspecies.

The inter-subspecific indica-japonica hybrid rice confer potential higher yield than the widely used indica-indica intra-subspecific hybrid rice. Nevertheless, the utilization of this strong heterosis is currently hindered by asynchronous diurnal floret opening time (DFOT) of indica and japonica parental lines. Here, we identify OsMYB8 as a key regulator of rice DFOT. OsMYB8 induces the transcription of JA-Ile synthetase OsJAR1, thereby regulating the expression of genes related to cell osmolality and cell wall remodeling in lodicules to promote floret opening. Natural variations of OsMYB8 promoter contribute to its differential expression, thus differential transcription of OsJAR1 and accumulation of JA-Ile in lodicules of indica and japonica subspecies. Furthermore, introgression of the indica haplotype of OsMYB8 into japonica effectively promotes DFOT in japonica. Our findings reveal an OsMYB8-OsJAR1 module that regulates differential DFOT in indica and japonica, and provide a strategy for breeding early DFOT japonica to facilitate breeding of indica-japonica hybrids.

pH change accompanying long-distance electrical signal controls systemic jasmonate biosynthesis.

Local damaging stimuli cause a rapid increase in the content of the defense phytohormone jasmonic acid (JA) and its biologically active derivative jasmonoyl-L-isoleucine (JA-Ile) in undamaged distal tissues. The increase in JA and JA-Ile levels was coincident with a rapid decrease in the levels of the precursor 12-oxo-phytodienoic acid (OPDA). The propagation of a stimulus-induced long-distance electrical signal, variation potential (VP), which is accompanied by intracellular changes in pH and Ca2+ levels, preceded systemic changes in jasmonate content. The decrease in pH during VP, mediated by transient inactivation of the plasma membrane H+-ATPase, induced the conversion of OPDA to JA, probably by regulating the availability of the OPDA substrate to JA biosynthetic enzymes. The regulation of systemic synthesis of JA and JA-Ile by the Ca2+ wave accompanying VP most likely occurs by the same mechanism of pH-induced conversion of OPDA to JA due to Ca2+-mediated decrease in pH as a result of H+-ATPase inactivation. Thus, the transient increase in intracellular Ca2+ levels and the transient decrease in intracellular pH are most likely the key mechanisms of VP-mediated regulation of jasmonate production in systemic tissues upon local stimulation.

Identification of transcription factor genes responsive to MeJA and characterization of a LaMYC2 transcription factor positively regulates lycorine biosynthesis in Lycoris aurea.

Jasmonates (JAs) are among the main phytohormones, regulating plant growth and development, stress responses, and secondary metabolism. As the major regulator of the JA signaling pathway, MYC2 also plays an important role in plant secondary metabolite synthesis and accumulation. In this study, we performed a comparative transcriptome analysis of Lycoris aurea seedlings subjected to methyl jasmonate (MeJA) at different treatment times. A total of 31,193 differentially expressed genes (DEGs) were identified by RNA sequencing. Among them, 732 differentially expressed transcription factors (TFs) comprising 51 TF families were characterized. The most abundant TF family was WRKY proteins (80), followed by AP2/ERF-EFR (67), MYB (59), bHLH (52), and NAC protein (49) families. Subsequently, by calculating the Pearson's correlation coefficient (PCC) between the expression level of TF DEGs and the lycorine contents, 41 potential TF genes (|PCC| >0.8) involved in lycorine accumulation were identified, including 36 positive regulators and 5 negative regulators. Moreover, a MeJA-inducible MYC2 gene (namely LaMYC2) was cloned on the basis of transcriptome sequencing. Bioinformatic analyses revealed that LaMYC2 proteins contain the bHLH-MYC_N domain and bHLH-AtAIB_like motif. LaMYC2 protein is localized in the cell nucleus, and can partly rescue the MYC2 mutant in Arabidopsis thaliana. LaMYC2 protein could interact with most LaJAZs (especially LaJAZ3 and LaJAZ4) identified previously. Transient overexpression of LaMYC2 increased lycorine contents in L. aurea petals, which might be associated with the activation of the transcript levels of tyrosine decarboxylase (TYDC) and phenylalanine ammonia lyase (PAL) genes. By isolating the 887-bp-length promoter fragment upstream of the start codon (ATG) of LaTYDC, we found several different types of E-box motifs (CANNTG) in the promoter of LaTYDC. Further study demonstrated that LaMYC2 was indeed able to bind the E-box (CACATG) present in the LaTYDC promoter, verifying that the pathway genes involved in lycorine biosynthesis could be regulated by LaMYC2, and that LaMYC2 has positive roles in the regulation of lycorine biosynthesis. These findings demonstrate that LaMYC2 is a positive regulator of lycorine biosynthesis and may facilitate further functional research of the LaMYC2 gene, especially its potential regulatory roles in Amaryllidaceae alkaloid accumulation in L. aurea.

Signalling responses in the bark and foliage of canker-susceptible and -resistant cypress clones inoculated with Seiridium cardinale.

The necrotrophic fungus Seiridium cardinale is the main responsible for Cypress Canker Disease (CCD), a pandemic affecting many Cupressaceae worldwide. The present study aims to elucidate the signalling of the early responses in the bark and foliage of CCD-susceptible and -resistant C. sempervirens clones to S. cardinale inoculation (SI and RI, respectively). In the bark of SI, a peaking production of ethylene (Et) and jasmonic acid (JA) occurred at 3 and 4 days post inoculation (dpi), respectively, suggesting an attempted plant response to the pathogen. A response that, however, was ineffective, as confirmed by the severe accumulation of malondialdehyde by-products at 13 dpi (i.e., lipid peroxidation). Differently, Et emission peaked in RI bark at 3 and 13 dpi, whereas abscisic acid (ABA) accumulated at 1, 4 and 13 dpi, resulting in a lower MDA accumulation (and unchanged levels of antioxidant capacity). In the foliage of SI, Et was produced at 1 and 9 dpi, whereas JA and salicylic acid (SA) accumulated at 1 and 3 dpi. Conversely, an increase of ABA and SA occurred at 1 dpi in the RI foliage. This outcome indicates that some of the observed metabolic alterations, mainly occurring as local defence mechanisms, might be able to gradually shift to a systemic resistance, although an accumulation of MDA was observed in both SI and RI foliage (but with an increased antioxidant capacity reported only in the resistant clone). We believe that the results reported here will be useful for the selection of clones able to limit the spread and damage of CCD.

NaWRKY70 is a key regulator of Nicotiana attenuata resistance to Alternaria alternata through regulation of phytohormones and phytoalexins biosynthesis.

Jasmonate (JA) and abscisic acid (ABA) are two major phytohormones involved in pathogen resistance. However, how their biosynthesis is regulated is not well understood. We silenced NaWRKY70 in wild tobacco Nicotiana attenuata and determined its role in regulating genes involved in the production of JA, ABA and the phytoalexin capsidiol in response to the fungal pathogen Alternaria alternata using techniques including electrophoretic mobility shift, chromatin immunoprecipitation, transient overexpression and virus-induced gene silencing. Silencing NaWRKY70 dramatically reduced both basal and A. alternata-induced jasmonoyl-isoleucine (JA-Ile) and ABA. Further evidence showed that NaWRKY70 directly binds to the W-boxes of the promoters of NaAOS and NaJAR4 (JA biosynthesis), NaNCED1 and NaXD1-like (ABA biosynthesis), and NaMPK4 (ABA signaling) to activate their expression, while binding but repressing the expression of NaCYP707A4-like3 (ABA degradation). Additionally, NaWRKY70 regulates capsidiol production through its key enzyme genes NaEASs and NaEAHs, and interacts with its regulator NaERF2-like to enhance their expression, whereas ABA negatively regulates capsidiol biosynthesis. Our results highlight the key role of NaWRKY70 in controlling both JA-Ile and ABA production, as well as capsidiol production, thus providing new insight into the defense mechanism of plant resistance to A. alternata.

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.

Tomato CYP94C1 inactivates bioactive JA-Ile to attenuate jasmonate-mediated defense during fruit ripening.

As the master regulators of the ET signaling pathway, EIL transcription factors directly activate the expression of CYP94C1 to inactivate bioactive JA-Ile, thereby attenuating JA-mediated defense during fruit ripening. Knockout of CYP94C1 improves tomato fruit resistance to necrotrophs without compromising fruit quality.

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

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

Contrasting plant transcriptome responses between a pierce-sucking and a chewing herbivore go beyond the infestation site.

BACKGROUND: Plants have acquired a repertoire of mechanisms to combat biotic stressors, which may vary depending on the feeding strategies of herbivores and the plant species. Hormonal regulation crucially modulates this malleable defense response. Jasmonic acid (JA) and salicylic acid (SA) stand out as pivotal regulators of defense, while other hormones like abscisic acid (ABA), ethylene (ET), gibberellic acid (GA) or auxin also play a role in modulating plant-pest interactions. The plant defense response has been described to elicit effects in distal tissues, whereby aboveground herbivory can influence belowground response, and vice versa. This impact on distal tissues may be contingent upon the feeding guild, even affecting both the recovery of infested tissues and those that have not suffered active infestation. RESULTS: To study how phytophagous with distinct feeding strategies may differently trigger the plant defense response during and after infestation in both infested and distal tissues, Arabidopsis thaliana L. rosettes were infested separately with the chewing herbivore Pieris brassicae L. and the piercing-sucker Tetranychus urticae Koch. Moderate infestation conditions were selected for both pests, though no quantitative control of damage levels was carried out. Feeding mode did distinctly influence the transcriptomic response of the plant under these conditions. Though overall affected processes were similar under either infestation, their magnitude differed significantly. Plants infested with P. brassicae exhibited a short-term response, involving stress-related genes, JA and ABA regulation and suppressing growth-related genes. In contrast, T. urticae elicited a longer transcriptomic response in plants, albeit with a lower degree of differential expression, in particular influencing SA regulation. These distinct defense responses transcended beyond infestation and through the roots, where hormonal response, flavonoid regulation or cell wall reorganization were differentially affected. CONCLUSION: These outcomes confirm that the existent divergent transcriptomic responses elicited by herbivores employing distinct feeding strategies possess the capacity to extend beyond infestation and even affect tissues that have not been directly infested. This remarks the importance of considering the entire plant's response to localized biotic stresses.

External jasmonic acid isoleucine mediates amplification of plant elicitor peptide receptor (PEPR) and jasmonate-based immune signalling.

Jasmonic acid-isoleucine (JA-Ile) is a plant defence hormone whose cellular levels are elevated upon herbivory and regulate defence signalling. Despite their pivotal role, our understanding of the rapid cellular perception of bioactive JA-Ile is limited. This study identifies cell type-specific JA-Ile-induced Ca2+ signal and its role in self-amplification and plant elicitor peptide receptor (PEPR)-mediated signalling. Using the Ca2+ reporter, R-GECO1 in Arabidopsis, we have characterized a monophasic and sustained JA-Ile-dependent Ca2+ signature in leaf epidermal cells. The rapid Ca2+ signal is independent of positive feedback by the JA-Ile receptor, COI1 and the transporter, JAT1. Microarray analysis identified up-regulation of receptors, PEPR1 and PEPR2 upon JA-Ile treatment. The pepr1 pepr2 double mutant in R-GECO1 background exhibits impaired external JA-Ile induced Ca2+ cyt elevation and impacts the canonical JA-Ile responsive genes. JA responsive transcription factor, MYC2 binds to the G-Box motif of PEPR1 and PEPR2 promoter and activates their expression upon JA-Ile treatment and in myc2 mutant, this is reduced. External JA-Ile amplifies AtPep-PEPR pathway by increasing the AtPep precursor, PROPEP expression. Our work shows a previously unknown non-canonical PEPR-JA-Ile-Ca2+ -MYC2 signalling module through which plants sense JA-Ile rapidly to amplify both AtPep-PEPR and jasmonate signalling in undamaged cells.

Integrative effects of phytohormones in the phenolic acids production in Salvia verticillata L. under multi-walled carbon nanotubes and methyl jasmonate elicitation.

Salvia verticillata L. is a well-known herb rich in rosmarinic acid (RA) and with therapeutic values. To better understand the possible roles of phytohormones in the production of phenolic acids in S. verticillata, in this work, we investigated some physiological and biochemical responses of the species to methyl jasmonate (MJ) and multi-walled carbon nanotubes (MWCNTs) as two effective elicitors. The leaves were sprayed with aqueous solutions containing 100 mg L-1 MWCNTs and 100 µM MJ and then harvested during interval times of exposure up to 96 h. The level of abscisic acid, as the first effective phytohormone, was altered in the leaves in response to MJ and MWCNTs elicitation (2.26- and 3.06-fold more than the control, respectively), followed by significant increases (P ˂ 0.05) detected in jasmonic acid and salicylic acid contents up to 8 h after exposure. Obtained data revealed that simultaneously with changes in phytohormone profiles, significant (P ˂ 0.05) rises were observed in the content of H2O2 (8.85- and 9.74-folds of control), and the amount of lipid peroxidation (10.18- and 17.01-folds of control) during the initial times after exposure to MJ and MWCNTs, respectively. Later, the content of phenolic acids increased in the elicited leaves due to changes in the transcription levels of key enzymes involved in their biosynthesis pathways, so 2.71- and 11.52-fold enhances observed in the RA content of the leaves after exposure to MJ and MWCNTs, respectively. It is reasonable to conclude that putative linkages between changes in some phytohormone pools lead to the accumulation of phenolic acids in the leaves of S. verticillata under elicitation. Overall, the current findings help us improve our understanding of the signal transduction pathways of the applied stimuli that led to enhanced secondary metabolite production in medicinal plants.

Galactinol Regulates JA Biosynthesis to Enhance Tomato Cold Tolerance.

Low temperatures can inhibit plant growth and development and reduce fruit yield. This study demonstrated that the expression of AnGolS1 from Ammopiptanthus nanus (A. nanus) encoding a galactinol synthase enhanced tomato cold tolerance. In AnGolS1-overexpressing plants, the jasmonic acid (JA) biosynthesis substrates 13-hydroperoxylinolenicacid and 12,13-epoxylinolenicacid were significantly accumulated, and the expression levels of the ethylene response factor (SlERF4-7) and serine protease inhibitor (SlSPI5) were increased. We speculated that there may be correlations among galactinol, ethylene signaling, the protease inhibitor, protease, and JA levels. The expression levels of SlERF4-7 and SlSPI5 as well as the JA content were significantly increased under exogenous galactinol treatment. Additionally, the expression of SlSPI5 was reduced in SlERF4-7-silenced plants, and SlERF4-7 was confirmed to bind to the dehydration-responsive element (DRE) of the SlSPI5 promoter. These results suggest that SlSPI5 is a target gene of the SlERF4-7 transcription factor. In addition, SlSPI5 interacted with cysteine protease (SlCPase), while SlCPase interacted with lipoxygenase (SlLOX5) and allene oxide synthase (SlAOS2). When SlCPase was silenced, JA levels increased and plant cold tolerance was enhanced. Therefore, galactinol regulates JA biosynthesis to enhance tomato cold tolerance through the SlERF4-7-SlSPI5-SlCPase-SlLOX5/SlAOS2 model. Overall, our study provides new perspectives on the role of galactinol in the JA regulatory network in plant adaptation to low-temperature stress.

The phenylalanine ammonia-lyase inhibitor AIP induces rice defence against the root-knot nematode Meloidogyne graminicola.

The phenylalanine ammonia-lyase (PAL) enzyme catalyses the conversion of l-phenylalanine to trans-cinnamic acid. This conversion is the first step in phenylpropanoid biosynthesis in plants. The phenylpropanoid pathway produces diverse plant metabolites that play essential roles in various processes, including structural support and defence. Previous studies have shown that mutation of the PAL genes enhances disease susceptibility. Here, we investigated the functions of the rice PAL genes using 2-aminoindan-2-phosphonic acid (AIP), a strong competitive inhibitor of PAL enzymes. We show that the application of AIP can significantly reduce the PAL activity of rice crude protein extracts in vitro. However, when AIP was applied to intact rice plants, it reduced infection of the root-knot nematode Meloidogyne graminicola. RNA-seq showed that AIP treatment resulted in a rapid but transient upregulation of defence-related genes in roots. Moreover, targeted metabolomics demonstrated higher levels of jasmonates and antimicrobial flavonoids and diterpenoids accumulating after AIP treatment. Furthermore, chemical inhibition of the jasmonate pathway abolished the effect of AIP on nematode infection. Our results show that disturbance of the phenylpropanoid pathway by the PAL inhibitor AIP induces defence in rice against M. graminicola by activating jasmonate-mediated defence.

Eggplant transcription factor SmMYB5 integrates jasmonate and light signaling during anthocyanin biosynthesis.

Low light conditions severely suppress anthocyanin synthesis in fruit skins, leading to compromised fruit quality in eggplant (Solanum melongena L.) production. In this study, we found that exogenous methyl-jasmonate (MeJA) application can effectively rescue the poor coloration of the eggplant pericarp under low light conditions. However, the regulatory relationship between jasmonate and light signaling for regulating anthocyanin synthesis remains unclear. Here, we identified a JA response factor, SmMYB5, as an anthocyanin positive regulator by applying RNA-sequencing and characterization of transgenic plants. Firstly, we resolved that SmMYB5 can interact with TRANSPARENT TESTA8 (SmTT8), an anthocyanin-promoted BASIC HELIX-LOOP-HELIX (bHLH) transcription factor, to form the SmMYB5-SmTT8 complex and activate CHALCONE SYNTHASE (SmCHS), FLAVANONE-3-HYDROXYLASE (SmF3H), and ANTHOCYANIN SYNTHASE (SmANS) promoters by direct binding. Secondly, we revealed that JA signaling repressors JASMONATE ZIM DOMAIN5 (SmJAZ5) and SmJAZ10 can interfere with the stability and transcriptional activity of SmMYB5-SmTT8 by interacting with SmMYB5. JA can partially rescue the transcriptional activation of SmF3H and SmANS promoters by inducing SmJAZ5/10 degradation. Thirdly, we demonstrated that the protein abundance of SmMYB5 is regulated by light. CONSTITUTIVELY PHOTOMORPHOGENIC1 (SmCOP1) interacts with SmMYB5 to trigger SmMYB5 degradation via the 26S proteasome pathway. Finally, we delineated a light-dependent JA-SmMYB5 signaling pathway that promotes anthocyanin synthesis in eggplant fruit skins. These results provide insights into the mechanism of the integration of JA and light signals in regulating secondary metabolite synthesis in plants.