Jasmonic Acid Biosynthetic Genes Research Articles

Overexpression of PtoMYB99 diminishes poplar tolerance to osmotic stress by suppressing ABA and JA biosynthesis

Drought poses a serious challenge to sustained plant growth and crop yields in the context of global climate change. Drought tolerance in poplars and their underlying mechanisms still remain largely unknown. In this article, we investigated the overexpression of PtoMYB99 – both a drought and abscisic acid (ABA) induced gene constraining drought tolerance in poplars (as compared with wild type poplars). First, we found that PtoMYB99-OE lines exhibited increased stomatal opening and conductance, higher transpiration and photosynthetic rates, as well as reduced levels of ABA and jasmonic acid (JA). Second, PtoMYB99-OE lines accumulated more reactive oxygen species (ROS), including H2O2 and O2−, as well as malonaldehyde (MDA), proline, and soluble sugar under osmotic stress; conversely, the activity of antioxidant enzymes (SOD, POD, and CAT), was weakened in the PtoMYB99-OE lines. Third, the expression of ABA biosynthetic genes, PtoNCED3.1 and PtoNCED3.2, as well as JA biosynthetic genes, PtoOPR3.1 and PtoOPR3.2, was significantly reduced in the PtoMYB99-OE lines under both normal conditions and osmotic stress. Based on our results, we conclude that the overexpression of PtoMYB99 compromises tolerance to osmotic stress in poplar. These findings contribute to the understanding of the role of the MYB genes in drought stress and the biosynthesis of ABA and JA.

GABA primes defense responses against Botrytis cinerea in tomato fruit by modulating ethylene and JA signaling pathways

This research set out to investigate the potential action mechanism of γ-aminobutyric acid (GABA) in the control of Botrytis cinerea (B. cinerea) in tomato fruit. The findings confirmed that 10 mM GABA treatment effectively lowered the disease incidence and lesion diameter of tomato fruit caused by B. cinerea. Meanwhile, GABA treatment maintained lower electrical conductivity, color change index and lycopene content. GABA alone had little effect on most disease resistance indexes, but it triggered faster and stronger defense responses after B. cinerea infection. These responses included increases in total phenolics and flavonoids accumulation as well as the activities of chitinase (CHI), β-1,3-glucanase (GLU), phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), and up-regulated expression of the pathogenesis-related genes (SlPR1, SlPR2a, SlPR2b, SlPR3a, SlPR3b and SlPR-STH2). Furthermore, GABA inhibited the expression of key synthesis genes of ethylene (SlACS2, SlACS4 and SlACO1) and the accumulation of a key metabolic intermediate 1-Aminocyclo-propane-l-carboxylic acid (ACC) in non-infected fruit, leading to a slight reduction in ethylene production. However, it also reduced the ethylene burst carried on by B. cinerea infection at the early storage and restored the ethylene peak at the end of storage. Furthermore, GABA up-regulated the expression level of SlERF6 directly but induced the up-regulation of SlERF2, SlERF.A4, SlERF.B12, SlERF.C6 and SlERF.H9 in a primed manner. In addition, GABA pretreatment markedly enhanced jasmonic acid (JA) content by activating the transcription of JA biosynthetic genes (SlLoxD, SlAOC and SlOPR3), up-regulated the downstream receptor gene SlCOI1 and down-regulated the suppressor gene SlJAZ2. These results demonstrated that tomato fruit treated with GABA can efficiently enhance resistance against B. cinerea through defense priming, and ethylene and JA signaling pathways are involved in this process.

Metabolic and Molecular Rearrangements of Sauvignon Blanc (Vitis vinifera L.) Berries in Response to Foliar Applications of Specific Dry Yeast.

Dry yeast extracts (DYE) are applied to vineyards to improve aromatic and secondary metabolic compound content and wine quality; however, systematic information on the underpinning molecular mechanisms is lacking. This work aimed to unravel, through a systematic approach, the metabolic and molecular responses of Sauvignon Blanc berries to DYE treatments. To accomplish this, DYE spraying was performed in a commercial vineyard for two consecutive years. Berries were sampled at several time points after the treatment, and grapes were analyzed for sugars, acidity, free and bound aroma precursors, amino acids, and targeted and untargeted RNA-Seq transcriptional profiles. The results obtained indicated that the DYE treatment did not interfere with the technological ripening parameters of sugars and acidity. Some aroma precursors, including cys-3MH and GSH-3MH, responsible for the typical aromatic nuances of Sauvignon Blanc, were stimulated by the treatment during both vintages. The levels of amino acids and the global RNA-seq transcriptional profiles indicated that DYE spraying upregulated ROS homeostatic and thermotolerance genes, as well as ethylene and jasmonic acid biosynthetic genes, and activated abiotic and biotic stress responses. Overall, the data suggested that the DYE reduced berry oxidative stress through the regulation of specific subsets of metabolic and hormonal pathways.

JA-mediated MYC2/LOX/AOS feedback loop regulates osmotic stress response in tea plant

Osmotic stress caused by low-temperature, drought and salinity was a prevalent abiotic stress in plant that severely inhibited plant development and agricultural yield, particularly in tea plant. Jasmonic acid (JA) is an important phytohormone involving in plant stress. However, underlying molecular mechanisms of JA modulated osmotic stress response remains unclear. In this study, high concentration of mannitol induced JA accumulation and increase of peroxidase activity in tea plant. Integrated transcriptome mined a JA signaling master, MYC2 transcription factor is shown as a hub regulator that induced by mannitol, expression of which positively correlated with JA biosynthetic genes (LOX and AOS) and peroxidase genes (PER). CsMYC2 was determined as a nuclei-localized transcription activator, furthermore, Protein-DNA interaction analysis indicated that CsMYC2 was positive regulator that activated the transcription of CsLOX7, CsAOS2, CsPER1 and CsPER3 via bound with their promoters, respectively. Suppression of CsMYC2 expression resulted in a reduced JA content and peroxidase activity and osmotic stress tolerance of tea plant. Overexpression of CsMYC2 in Arabidopsis improved JA content, peroxidase activity and plants tolerance against mannitol stress. Together, we proposed a positive feedback loop mediated by CsMYC2, CsLOX7 and CsAOS2 which constituted to increase the tolerance of osmotic stress through fine-tuning the accumulation of JA levels and increase of POD activity in tea plant.

Cytokinin Promotes Jasmonic Acid Accumulation in the Control of Maize Leaf Growth.

Plant organ growth results from the combined activity of cell division and cell expansion. The co-ordination of these two processes depends on the interplay between multiple hormones that determine the final organ size. Using the semidominant Hairy Sheath Frayed1 (Hsf1) maize mutant that hypersignals the perception of cytokinin (CK), we show that CK can reduce leaf size and growth rate by decreasing cell division. Linked to CK hypersignaling, the Hsf1 mutant has an increased jasmonic acid (JA) content, a hormone that can inhibit cell division. The treatment of wild-type seedlings with exogenous JA reduces maize leaf size and growth rate, while JA-deficient maize mutants have increased leaf size and growth rate. Expression analysis revealed the increased transcript accumulation of several JA pathway genes in the Hsf1 leaf growth zone. A transient treatment of growing wild-type maize shoots with exogenous CK also induced the expression of JA biosynthetic genes, although this effect was blocked by the co-treatment with cycloheximide. Together, our results suggest that CK can promote JA accumulation, possibly through the increased expression of specific JA pathway genes.

Single-Bud Expression Analysis of Bud Dormancy Factors in Peach.

Transcriptomic and gene expression analysis have greatly facilitated the identification and characterization of transcriptional regulatory factors and effectors involved in dormancy progression and other physiological processes orchestrated during bud development in peach and other temperate fruit species. Gene expression measurements are most usually based on average values from several or many individual buds. We have performed single-bud gene analysis in flower buds of peach across dormancy release using amplicons from the master regulatory DORMANCY-ASSOCIATED MADS-BOX (DAM) factors, several jasmonic acid biosynthetic genes, other genes related to flowering development, cell growth resumption, and abiotic stress tolerance. This analysis provides a close view on gene-specific, single-bud variability throughout the developmental shift from dormant to dormancy-released stages, contributing to the characterization of putative co-expression modules and other regulatory aspects in this particular tissue.

CsTPS21 encodes a jasmonate-responsive monoterpene synthase producing β-ocimene in citrus against Asian citrus psyllid

Huanglongbing (HLB), spread by the Asian citrus psyllid (ACP), is a widespread, devastating disease that causes significant losses in citrus production. Therefore, controlling the ACP infestation and HLB infection is very important for citrus production. The aim of our study was to identify any citrus volatile which could be used as a repellent or less attractant towards ACP, and to envisage the potential of this strategy to control HLB spread. The present study identified a terpene synthase (TPS)-encoding gene CsTPS21 in citrus plants, and this gene was predicted to encode a monoterpene synthase and had an amino acid sequence similar to β-ocimene synthase. CsTPS21 was significantly upregulated by ACP infestation and methyl jasmonic acid (MeJA) treatment but downregulated by salicylic acid (SA). Further heterologous gene expression studies in yeast cells and tobacco plants indicated that the protein catalyzed the formation of β-ocimene, which acted as an ACP repellent. Detailed analysis of tobacco overexpressing CsTPS21 showed that CsTPS21 synthesizing β-ocimene regulated jasmonic acid (JA)-associated pathways by increasing the JA accumulation and inducing the JA biosynthetic gene expression to defend against insect infestation. These findings provide a basis to plan strategies to manage HLB in the field using β-ocimene and CsTPS21 as candidates.

Airborne Methyl Jasmonate is Metabolized to Jasmonic Acid and 12‐Hydroxyjasmonic Acid, and Induces Jasmonate Biosynthesis in Marchantia polymorpha

AbstractMethyl jasmonate (MeJA) is a volatile jasmonate compound commonly used to induce defense responses in spermatophytes. This study reports that airborne MeJA‐d3, deuterated MeJA, increases the levels of (dinor‐)12‐oxo‐phytodienoic acids [(dn‐)OPDAs] and jasmonic acid (JA) as well as JA‐d3 and 12‐hydroxyjasmonic acid‐d2 (12‐OH‐JA‐d2), MeJA‐d3 metabolites, in the model bryophyte Marchantia polymorpha. Enhancement of JA biosynthesis was substantiated by the expression of JA biosynthetic genes induced by airborne MeJA. Additionally, each of enantiomers, (+)‐MeJA and (−)‐MeJA, was observed to induce the accumulation of JA and (dn‐)OPDAs in M. polymorpha. This study demonstrates that airborne MeJA is metabolized to JA and 12‐OH‐JA, and induces JA biosynthesis in M. polymorpha. Moreover, the transient increase in endogenous JA level after airborne MeJA treatment provides concrete evidence that M. polymorpha biosynthesizes JA.

BcOPR3 Mediates Defense Responses to Biotrophic and Necrotrophic Pathogens in Arabidopsis and Non-heading Chinese Cabbage.

In plants, the salicylic acid (SA) and jasmonic acid (JA) signaling pathways usually mediate the defense response to biotrophic and necrotrophic pathogens, respectively. Our previous work showed that after non-heading Chinese cabbage (NHCC) was infected with the biotrophic pathogen Hyaloperonospora parasitica, expression of the JA biosynthetic gene BcOPR3 is induced; however, its molecular mechanism remains unclear. Here, we overexpressed BcOPR3 in Arabidopsis and silenced BcOPR3 in NHCC001 plants to study the defensive role of BcOPR3 in plants against pathogen invasion. The results showed that overexpression of BcOPR3 increased the susceptibility of Arabidopsis to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) but enhanced its resistance to Botrytis cinerea. BcOPR3-silenced NHCC001 plants with a 50% reduction in BcOPR3 expression increased their resistance to downy mildew by reducing the hyphal density and spores of H. parasitica. In addition, BcOPR3-partly silenced NHCC001 plants were also resistant to B. cinerea, which could be the result of a synergistic effect of JA and SA. These findings indicate a complicated role of BcOPR3 in the mediating defense responses to biotrophic and necrotrophic pathogens.

Transcription factor CsESE3 positively modulates both jasmonic acid and wax biosynthesis in citrus

PLIP lipases can initiate jasmonic acid (JA) biosynthesis. However, little is known about the transcriptional regulation of this process. In this study, an ERF transcription factor (CsESE3) was found to be co-expressed with all necessary genes for JA biosynthesis and several key genes for wax biosynthesis in transcriptomes of ‘Newhall’ navel orange. CsESE3 shows partial sequence similarity to the well-known wax regulator SHINEs (SHNs), but lacks a complete MM protein domain. Ectopic overexpression of CsESE3 in tomato (OE) resulted in reduction of fruit surface brightness and dwarf phenotype compared to the wild type. The OE tomato lines also showed significant increases in the content of wax and JA and the expression of key genes related to their biosynthesis. Overexpression of CsESE3 in citrus callus and fruit enhanced the JA content and the expression of JA biosynthetic genes. Furthermore, CsESE3 could bind to and activate the promoters of two phospholipases from the PLIP gene family to initiate JA biosynthesis. Overall, this study indicated that CsESE3 could mediate JA biosynthesis by activating PLIP genes and positively modulate wax biosynthesis. The findings provide important insights into the coordinated control of two defense strategies of plants represented by wax and JA biosynthesis.

The E3 ubiquitin ligase RING1 interacts with COP9 Signalosome Subunit 4 to positively regulate resistance to root-knot nematodes in Solanum lycopersicum L.

Globally, root-knot nematodes (RKNs) cause massive production losses in all major crops. E3 ubiquitin ligases are involved in plant growth, development and immune response. But their roles in plant defense against RKNs are largely unclear. Here, we show that tomato E3 ubiquitin ligase RING1 interacts with COP9 Signalosome Subunit 4 (CSN4) which is essential for jasmonic acid (JA)-dependent basal defense against RKNs. Tissue-specific expression analysis showed that RING1 expression was the highest in tomato roots and the expression was significantly increased with RKN (Meloidogyne incognita) infection. Compared with the wild-type plants, the number of egg masses in roots significantly increased in the ring1 mutants, while RING1 overexpression conferred resistance against RKNs. Furthermore, RKN infection increased the accumulation of CSN4 protein in the roots of wild-type plants, which was largely compromised in the ring1 mutants but was enhanced in the RING1 overexpressing plants. The RKN-induced transcripts of JA biosynthetic and signaling genes as well as the accumulation of JA and JA-isoleucine were compromised in ring1 mutants but were increased in RING1 overexpressing plants. These results suggest that RING1 positively regulates JA-dependent basal defense against RKNs by interacting with CSN4 proteins.

Jasmonic acid biosynthetic genes TgLOX4 and TgLOX5 are involved in daughter bulb development in tulip (Tulipa gesneriana).

Tulip bulbs are modified underground stems that originate from axillary meristems of mother bulb scales. Hormones, including jasmonic acids (JAs), play key roles in the regulation of tulip bulb development. Here, we compared variations in daughter bulb development through transcriptomic profiling analysis and characterized the functions of JA biosynthesis-related genes during daughter bulb enlargement. The results showed that tulip cultivars exhibited contrasting bulb size variations. Transcriptomic analyses revealed that genes involved in plant hormones and development, including the two lipoxygenase genes TgLOX4 and TgLOX5, showed significant changes in expression following tulip bulb growth. Ectopic overexpression of TgLOX4 and TgLOX5 in Arabidopsis enhanced endogenous JA content, improved plant growth, and increased lateral root numbers. Silencing of these two genes in tulip repressed the growth of daughter bulbs. Furthermore, exogenous JA treatment promoted tulip bulb growth, whereas the JA biosynthesis inhibitor sodium diethyldithiocarbamate (DIECA) inhibited this process. This study offers supporting evidence for the involvement of tulip TgLOX4 and TgLOX5 in the regulation of daughter bulb growth and development.

Integrated transcriptomic and metabolic analyses reveal that ethylene enhances peach susceptibility to Lasiodiplodia theobromae-induced gummosis.

Gummosis, one of the most detrimental diseases to the peach industry worldwide, can be induced by Lasiodiplodia theobromae. Ethylene (ET) is known to trigger the production of gum exudates, but the mechanism underlying fungus-induced gummosis remains unclear. In this study, L. theobromae infection triggered the accumulation of ET and jasmonic acid (JA) but not salicylic acid (SA) in a susceptible peach variety. Gaseous ET and its biosynthetic precursor increased gum formation, whereas ET inhibitors repressed it. SA and methyl-jasmonate treatments did not influence gum formation. RNA-seq analysis indicated that L. theobromae infection and ET treatment induced a shared subset of 1808 differentially expressed genes, which were enriched in the category "starch and sucrose, UDP-sugars metabolism". Metabolic and transcriptional profiling identified a pronounced role of ET in promoting the transformation of primary sugars (sucrose, fructose, and glucose) into UDP-sugars, which are substrates of gum polysaccharide biosynthesis. Furthermore, ethylene insensitive3-like1 (EIL1), a key transcription factor in the ET pathway, could directly target the promoters of the UDP-sugar biosynthetic genes UXS1a, UXE, RGP and MPI and activate their transcription, as revealed by firefly luciferase and yeast one-hybrid assays. On the other hand, the supply of SA and inhibitors of ET and JA decreased the lesion size. ET treatment reduced JA levels and the transcription of the JA biosynthetic gene OPR but increased the SA content and the expression of its biosynthetic gene PAL. Overall, we suggest that endogenous and exogenous ET aggravate gummosis disease by transactivating UDP-sugar metabolic genes through EIL1 and modulating JA and SA biosynthesis in L. theobromae-infected peach shoots. Our findings shed light on the molecular mechanism by which ET regulates plant defense responses in peach during L. theobromae infection.

β-Cyclocitral, a Master Regulator of Multiple Stress-Responsive Genes in Solanum lycopersicum L. Plants

β-cyclocitral (βCC), a major apocarotenoid of β-carotene, enhances plants’ defense against environmental stresses. However, the knowledge of βCC’s involvement in the complex stress-signaling network is limited. Here we demonstrate how βCC reprograms the transcriptional responses that enable Solanum lycopersicum L. (tomato) plants to endure a plethora of environmental stresses. Comparative transcriptome analysis of control and βCC-treated tomato plants was done by generating RNA sequences in the BGISEQ-500 platform. The trimmed sequences were mapped on the tomato reference genome that identifies 211 protein-coding differentially expressed genes. Gene ontology and Kyoto Encyclopedia of Genes and Genomes analysis and their enrichment uncovered that only upregulated genes are attributed to the stress response. Moreover, 80% of the upregulated genes are functionally related to abiotic and biotic stresses. Co-functional analysis of stress-responsive genes revealed a network of 18 genes that code for heat shock proteins, transcription factors (TFs), and calcium-binding proteins. The upregulation of jasmonic acid (JA)-dependent TFs (MYC2, MYB44, ERFs) but not the JA biosynthetic genes is surprising. However, the upregulation of DREB3, an abscisic acid (ABA)-independent TF, validates the unaltered expression of ABA biosynthetic genes. We conclude that βCC treatment upregulates multiple stress-responsive genes without eliciting JA and ABA biosynthesis.

Transcriptome and Oxylipin Profiling Joint Analysis Reveals Opposite Roles of 9-Oxylipins and Jasmonic Acid in Maize Resistance to Gibberella Stalk Rot

Gibberella stalk rot caused by Fusarium graminearum is one of the devastating diseases of maize that causes significant yield losses worldwide. The molecular mechanisms regulating defense against this pathogen remain poorly understood. According to recent studies, a major oxylipin hormone produced by 13-lipoxygenases (LOX) namely jasmonic acid (JA) has been associated with maize susceptibility to GSR. However, the specific roles of numerous 9-LOX-derived oxylipins in defense against Gibberella stalk rot (GSR) remain unexplained. In this study, we have shown that disruption of a 9-LOX gene, ZmLOX5, resulted in increased susceptibility to GSR, indicating its role in defense. To understand how ZmLOX5 regulates GSR resistance, we conducted transcriptome and oxylipin profiling using a zmlox5-3 mutant and near-isogenic wild type B73, upon infection with F. graminearum. The results showed that JA biosynthetic pathway genes were highly up-regulated, whereas multiple 9-LOX pathway genes were down-regulated in the infected zmlox5-3 mutant. Furthermore, oxylipin profiling of the mutant revealed significantly higher contents of several jasmonates but relatively lower levels of 9-oxylipins in zmlox5-3 upon infection. In contrast, B73 and W438, a more resistant inbred line, displayed relatively lower levels of JAs, but a considerable increase of 9-oxylipins. These results suggest antagonistic interaction between 9-oxylipins and JAs, wherein 9-oxylipins contribute to resistance while JAs facilitate susceptibility to F. graminearum.

TaWRKY13-A Serves as a Mediator of Jasmonic Acid-Related Leaf Senescence by Modulating Jasmonic Acid Biosynthesis.

Leaf senescence is crucial for crop yield and quality. Transcriptional regulation is a key step for integrating various senescence-related signals into the nucleus. However, few regulators of senescence implicating transcriptional events have been functionally characterized in wheat. Based on our RNA-seq data, we identified a WRKY transcription factor, TaWRKY13-A, that predominately expresses at senescent stages. By using the virus-induced gene silencing (VIGS) method, we manifested impaired transcription of TaWRKY13-A leading to a delayed leaf senescence phenotype in wheat. Moreover, the overexpression (OE) of TaWRKY13-A accelerated the onset of leaf senescence under both natural growth condition and darkness in Brachypodium distachyon and Arabidopsis thaliana. Furthermore, by physiological and molecular investigations, we verified that TaWRKY13-A participates in the regulation of leaf senescence via jasmonic acid (JA) pathway. The expression of JA biosynthetic genes, including AtLOX6, was altered in TaWRKY13-A-overexpressing Arabidopsis. We also demonstrated that TaWRKY13-A can interact with the promoter of AtLOX6 and TaLOX6 by using the electrophoretic mobility shift assay (EMSA) and luciferase reporter system. Consistently, we detected a higher JA level in TaWRKY13-A-overexpressing lines than that in Col-0. Moreover, our data suggested that TaWRKY13-A is partially functional conserved with AtWRKY53 in age-dependent leaf senescence. Collectively, this study manifests TaWRKY13-A as a positive regulator of JA-related leaf senescence, which could be a new clue for molecular breeding in wheat.

Methyl jasmonate‐induced resistance to Delia platura (Diptera: Anthomyiidae) in Lupinus mutabilis

Andean lupin (Lupinus mutabilis Sweet) is an important leguminous crop from South America with a high protein content. In Ecuador, lupin yields are severely affected by the infestation of Delia platura larvae on germinating seeds. The application of elicitor molecules with activity against herbivorous insects to control D. platura infestation constitutes an unexplored and promising alternative for chemical insecticides. In this study, methyl jasmonate (MeJA), hexanoic acid, menadione sodium bisulfite, and DL-β-aminobutyric acid were evaluated for their ability to induce resistance against D. platura in three commercial lupin cultivars. Only seeds pretreated with MeJA significantly impaired insect performance during choice and no-choice assays. Additionally, fitness indicators such as seed germination and growth were not affected by MeJA treatment. To investigate the molecular mechanisms behind the MeJA-mediated resistance, RT-qPCR assays were performed. First, RT-qPCR reference genes were validated, showing that LmUBC was the most stable reference gene. Next, expression analysis over time revealed that MeJA application up-regulated the activity of the jasmonic acid biosynthetic genes LmLOX2 and LmAOS, together with other jasmonate-related defense genes, such as LmTPS1, LmTPS4, LmPI2, LmMBL, LmL/ODC, LmCSD1, and LmPOD. This study indicates that MeJA can be used as an environmentally friendly elicitor molecule to protect Andean lupin from D. platura attack without fitness cost. MeJA application induces plant defense responses to insects in Andean lupin that may be modulated by the onset of terpenoid biosynthesis, proteinase inhibitors, lectins, polyamines, and antioxidative enzymes. © 2021 Society of Chemical Industry.

Overexpression of LYK4, a lysin motif receptor with non-functional kinase domain, enhances tolerance to Alternaria brassicicola and increases trichome density in Brassica juncea

Lysin motif receptor-like kinases (LYKs) are involved in the recognition of chitin and activation of plant immune response. In this study, we found LYK4 to be strongly induced in resistant Sinapis alba compared with susceptible Brassica juncea on challenge with Alternaria brassicicola. In silico analysis and in vitro kinase assay revealed that despite the presence of canonical protein kinase fold, B.juncea LYK4 (BjLYK4) lacks several key residues of a prototype protein kinase which renders it catalytically inactive. Transient expression analysis confirmed that fluorescently tagged BjLYK4 localizes specifically to the plasma membrane. Overexpression (OE) of BjLYK4 in B. juncea enhanced tolerance against A. brassicicola. Interestingly, the OE lines also exhibited a novel trichome dense phenotype and increased jasmonic acid (JA) responsiveness. We further showed that many chitin responsive WRKY transcription factors and JA biosynthetic genes were strongly induced in the OE lines on challenge with the pathogen. Moreover, several JA inducible trichome developmental genes constituting the WD-repeat/bHLH/MYB activator complex were also upregulated in the OE lines compared with vector control and RNA interference line. These results suggest that BjLYK4 plays an essential role in chitin-dependent activation of defense response and chitin independent trichome development likely by influencing the JA signaling pathway.

Induction of jasmonic acid biosynthetic genes inhibits Arabidopsis growth in response to low boron.

The essential micronutrient boron (B) has key roles in cell wall integrity and B deficiency inhibits plant growth. The role of jasmonic acid (JA) in plant growth inhibition under B deficiency remains unclear. Here, we report that low B elevates JA biosynthesis in Arabidopsis thaliana by inducing the expression of JA biosynthesis genes. Treatment with JA inhibited plant growth and, a JA biosynthesis inhibitor enhanced plant growth, indicating that the JA induced by B deficiency affects plant growth. Furthermore, examination of the JA signaling mutants jasmonate resistant1, coronatine insensitive1‐2, and myc2 showed that JA signaling negatively regulates plant growth under B deficiency. We identified a low‐B responsive transcription factor, ERF018, and used yeast one‐hybrid assays and transient activation assays in Nicotiana benthamiana leaf cells to demonstrate that ERF018 activates the expression of JA biosynthesis genes. ERF018 overexpression (OE) lines displayed stunted growth and up‐regulation of JA biosynthesis genes under normal B conditions, compared to Col‐0 and the difference between ERF018 OE lines and Col‐0 diminished under low B. These results suggest that ERF018 enhances JA biosynthesis and thus negatively regulates plant growth. Taken together, our results highlight the importance of JA in the effect of low B on plant growth.

Novel crosstalk between ethylene- and jasmonic acid-pathway responses to a piercing-sucking insect in rice.

Ethylene (ET) and jasmonic acid (JA) play important roles in plant defenses against biotic stresses. Crosstalk between JA and ET has been well studied in mediating pathogen resistance, but its roles in piercing-sucking insect resistance are unclear. The brown planthopper (BPH; Nilaparvata lugens) is the most notorious piercing-sucking insect specific to rice (Oryza sativa) that severely affects yield. A genetic analysis revealed that OsEBF1 and OsEIL1, which are in the ET signaling pathway, positively and negatively regulated BPH resistance, respectively. Molecular and biochemical analyses revealed direct interactions between OsEBF1 and OsEIL1. OsEBF1, an E3 ligase, mediated the degradation of OsEIL1 through the ubiquitination pathway, indicating the negative regulation of the ET-signaling pathway in response to BPH infestation. An RNA sequencing analysis revealed that a JA biosynthetic pathway-related gene, OsLOX9, was downregulated significantly in the oseil1 mutant. Biochemical analyses, including yeast one-hybrid, dual luciferase, and electrophoretic mobility shift assay, confirmed the direct regulation of OsLOX9 by OsEIL1. This study revealed the synergistic and negative regulation of JA and ET pathways in response to piercing-sucking insect attack. The synergistic mechanism was realized by transcriptional regulation of OsEIL1 on OsLOX9. OsEIL1-OsLOX9 is a novel crosstalk site in these two phytohormone signaling pathways.