Endogenous Jasmonic Acid Research Articles

Changing light promotes isoflavone biosynthesis in soybean pods and enhances their resistance to mildew infection.

Mildew severely reduces soybean yield and quality, and pods are the first line of defence against pathogens. Maize-soybean intercropping (MSI) reduces mildew incidence on soybean pods; however, the mechanism remains unclear. Changing light (CL) from maize shading is the most important environmental feature in MSI. We hypothesized that CL affects isoflavone accumulation in soybean pods, affecting their disease resistance. In the present study, shading treatments were applied to soybean plants during different developmental stages according to various CL environments under MSI. Chlorophyll fluorescence imaging (CFI) and classical evaluation methods confirmed that CL, especially vegetative stage shading (VS), enhanced pod resistance to mildew. Further metabolomic analyses and exogenous jasmonic acid (JA) and biosynthesis inhibitor experiments revealed the important relationship between JA and isoflavone biosynthesis, which had a synergistic effect on the enhanced resistance of CL-treated pods to mildew. VS promoted the biosynthesis and accumulation of constitutive isoflavones upstream of the isoflavone pathway, such as aglycones and glycosides, in soybean pods. When mildew infects pods, endogenous JA signalling stimulated the biosynthesis of downstream inducible malonyl isoflavone (MIF) and glyceollin to improve pod resistance.

Jasmonate regulates the FAMA/mediator complex subunit 8-THIOGLUCOSIDE GLUCOHYDROLASE 1 cascade and myrosinase activity.

Myrosinases are β-thioglucoside glucosidases that are unique to the Brassicales order. These enzymes hydrolyze glucosinolates to produce compounds that have direct antibiotic effects or that function as signaling molecules in the plant immune system, protecting plants from pathogens and insect pests. However, the effects of jasmonic acid (JA), a plant hormone that is crucial for plant disease resistance, on myrosinase activity remain unclear. Here, we systematically studied the effects of JA on myrosinase activity and explored the associated internal transcriptional regulation mechanisms. Exogenous application of JA significantly increased myrosinase activity, while the inhibition of endogenous JA biosynthesis and signaling reduced myrosinase activity. In addition, some myrosinase genes in Arabidopsis (Arabidopsis thaliana) were upregulated by JA. Further genetic and biochemical evidence showed that transcription factor FAMA interacted with a series of JASMONATE ZIM-DOMAIN proteins and affected JA-mediated myrosinase activity. However, among the JA-upregulated myrosinase genes, only THIOGLUCOSIDE GLUCOHYDROLASE 1 (TGG1) was positively regulated by FAMA. Further biochemical analysis showed that FAMA bound to the TGG1 promoter to directly mediate TGG1 expression in conjunction with Mediator complex subunit 8 (MED8). Together, our results provide evidence that JA acts as an important signal upstream of the FAMA/MED8-TGG1 pathway to positively regulate myrosinase activity in Arabidopsis.

Further insights into how low-light signaling delays leaf senescence in soybean under high-temperature

Plants go through several physiological modifications in their life cycle. Leaf senescence (LS) occurs at the later stage of plant development but can also be initiated by high temperature (HT) stress. LS involves the breakdown of certain key developmental processes in plants, which affect leaf greenness, thereby decreasing plant photosynthetic performance. Light signaling pathway modulates plant growth processes under high-temperature stress, suggesting that light and temperature signaling pathways are linked. However, our knowledge of how light signaling pathways delay LS in soybean under HT remains incomplete. Therefore, this study aimed to investigate how low light signaling pathway delays LS in soybean under HT stress. The results showed that low light signaling delayed LS in soybean under high-temperature stress. Our gas exchange analysis showed that low light signaling improved soybean photosynthetic process and chlorophyll contents under HT stress. Further analysis indicated that low light treatment improved soybean soluble sugar, starch, and free amino acids of plants exposed to HT stress. The phytohormones analysis suggested that under low light, plants accumulated endogenous jasmonic acid (JA) and salicylic acid (SA) when exposed to HT stress. The transcriptional analysis suggested that soybean STAY-GREEN genes (GmSGR1and GmSGR2), sucrose phosphate synthase genes (GmSPS1 and GmSPS2), and starch synthase genes (GmAGP1 and GmUGP1−1) were upregulated in the high-temperature and low light treatment. Again, the JA defense pathway genes GmPDF1.2, GmJAR1.1 GmFAD3.1, and GmPR4.2 expression levels were significantly upregulated in the high-temperature and low light treatment as compared to SA defense pathway genes GmSID2, GmEDS5, GmNPR1, and GmPR1. The regulation mechanisms involving how low light signaling delays leaf senescence in soybean under high temperature through improved photosynthetic rate and JA defense signaling activation are discussed.

Volatile organic compound and endogenous phytohormone characteristics during callus browning in Aquilaria sinensis

Callus browning, a common feature in plant cell cultures, has hardly been explored in Aquilaria sinensis. Here, the volatile organic compounds (VOCs) were characterized during the browning of A. sinensis cells using Gas Chromatography-Mass Spectrometry (GC–MS), and total sesquiterpene accumulation was significantly induced and peaked during A. sinensis callus browning, after 60 days of callus growth. Additionally, 14 types of sesquiterpenes were detected in the browning A. sinensis callus, with greater sesquiterpene diversity than in the ones treated with methyl jasmonate and salicylic acid (SA) in a previous study. To further evaluate the mechanism of regulation of agarwood sesquiterpenes during cell browning in A. sinensis, changes on phytohormone concentrations were explored using ultra-performance liquid chromatography-electrospray tandem mass spectrometry system (UPLC-ESI-MS/MS). Both endogenous jasmonic acid and SA, key plant defense hormones, increased during A. sinensis callus browning. 1-aminocyclopropanecarboxylic acid, an ethylene (ET) precursor, decreased significantly after A. sinensis callus browning. Conversely, two primary growth hormones, auxin and cytokinin, exhibited opposite trends, suggesting that they also play roles in agarwood sesquiterpene accumulation. Our results potentially offer novel insights that could facilitate the production valuable phytochemical compounds such as agarwood sesquiterpenes, using plant cell cultures treated with appropriate phytohormone combinations.

The exploration of methyl jasmonate on the tanshinones biosynthesis in hair roots of Salvia miltiorrhiza Bunge and Salvia castanea f. tomentosa Stib

Salvia miltiorrhiza Bunge (SMB) is a traditional Chinese medicinal material, its ketones have very important medicinal value. Salvia castanea f. tomentosa Stib (SCT) mainly distributed in Nyingchi, Tibet. Its pharmacological effects are similar to SMB, but its tanshinones are higher than the latter. Methyl jasmonate (MJ) as an inducer can induce the synthesis of tanshinones in SMB and SCT. However, the specific mechanism of action is still ambiguous. Therefore, this study used SMB and SCT hair root as an experimental material and MJ as a variable. In this study, we not only compared the content of endogenous jasmonic acid (JA) and MJ in SMB and SCT; but also compared the differences in the mechanism of action of MJ on the two. Our research has reached the following conclusions: firstly, MJ promotes the accumulation of tanshinones and related ingredients in the metabolic pathways of SMB and SCT. After MJ treatment, the content of related components and gene expression are increased. Secondly, it is not as previously reported that SCT has a higher response to MJ than SMB. Our experimental results show that the overall response of the two to MJ has no significant difference. There is only a difference between the individual components. It is speculated that the different responses of secondary metabolism-related genes to MJ may lead to different metabolic responses of tanshinones between the two.

Transcriptome and plant hormone analyses provide new insight into the molecular regulatory networks underlying hybrid lethality in cabbage (Brassica oleracea)

Comparative morphological, transcriptomic and phytohormone analyses reveal a defence network leading to PCD involved in cabbage hybrid lethality. Hybrid lethality (HL) plays an essential role in the stability of a population by blocking gene exchange between species, but the molecular mechanism remains largely undetermined. In this study, we performed phenotype, transcriptome and plant hormone analyses of HL in cabbage. Phenotype analysis confirmed that HL is characterised by a typical programmed cell death (PCD) process. A time-resolved RNA-Seq identified 2724 differentially expressed genes (DEGs), and functional annotations analyses revealed that HL was closely associated with the defence response. A defence regulation network was constructed based on the plant-pathogen interaction pathway and MAPK signalling pathway, which comprised DEGs related to Ca2+ and hydrogen peroxide (H2O2) leading to PCD. Moreover, important DEGs involved in hormone signal transduction pathways including salicylic acid (SA) and jasmonic acid (JA) were identified, which were further confirmed by endogenous and exogenous SA and JA measurements. Our results identified key genes and pathways in the regulating network of HL in cabbage, and might open the gate for revealing the molecular mechanism of HL in plants.

Application of jasmonic acid at the stage of visible brown necrotic spots in Magnaporthe oryzae infection as a novel and environment-friendly control strategy for rice blast disease.

Rice blast disease is one of the most common rice diseases worldwide. It is essential to improve disease resistance through environment-friendly methods, while maintaining yield and quality parameters. In this study, jasmonic acid (JA), a plant hormone with anti-fungal activity, was obtained, at both low (100 μmol/L) and high (400 μmol/L) concentrations in rice leaves, before, during, and after infection, respectively. JA could inhibit germination and appressorium formation of rice blast spores in a dose-dependent manner. A total of 400-μmol/L JA treatment significantly enhanced cell viability and endogenous JA level in rice leaves. Furthermore, rice leaves inoculated with Magnaporthe oryzae and sprayed with JA 72 h post-inoculation showed the maximum symptom relief and the highest endogenous JA production among all treatment approaches. The expressions of defense-related genes, OsPR10a and OsAOS2, were highly up-regulated in response to JA, whereas OsEDS1 was down-regulated. Hence, we revealed that exogenous JA could activate JA signaling to effectively control the symptoms of rice blast.

Effect of methyl jasmonate on aphid resistance of chrysanthemum.

We examined the effects of methyl jasmonate on aphid resistance of Chrysanthemum 'Hangbai'. Leaves of chrysanthemum cuttings were sprayed by methyl jasmonic with different concentrations (0.01, 0.05, 0.1, 0.5 and 1 mmol·L-1) and then inoculated with the aphids Macrosiphoniella sanborni. The following parameters are measured, including protective enzymes activities, defense enzyme activities, osmotic substances, secondary metabolites, and key genes of the jasmonic signaling pathway. The relationship between aphid resistance and the jasmonic signaling pathway in chrysanthemum was probed. The results showed that, under the treatments of all the five concentrations of methyl jasmonic, the activities of leaf protective enzymes and defense enzymes as well as the contents of secondary metabolite were increased in Chrysanthemum, whereas the contents of malondialdehyde and soluble sugar were reduced. Moreover, exogenous methyl jasmonate treatment induced the expression of CmAOS and CmCOI1, enhanced the content of endogenous jasmonic acid and the aphid resistance of chrysanthemum.

Abscisic acid in preservation of Taraxacum pieninicum in the form of synthetic seeds in slow growth conditions

Taraxacum pieninicum Pawł. is listed as critically endangered species, for which currently applied protection methods are insufficient. The aim of this study was to investigate the possibility of T. pieninicum storage in the form of synthetic seeds under slow-growth conditions in combination with ABA treatment, as one of the ex situ protection methods of this species. The obtained results indicated that darkness was much more favorable condition for synseed storage and did not generate additional stress during cold exposure in contrast to the light conditions. The preculture of shoot tips on the medium supplemented with ABA led to a decrease in the shoots proliferation rate and inhibition of their growth. ABA clearly inhibited growth of the encapsulated shoot tips also during cold storage. Biochemical parameters showed that ABA effectively reduced the negative effect of the cold stress, what was found on the basis of analyzes of H2O2 and TBARS levels in the stored material. Moreover, synseeds stored under light conditions and treated with ABA exhibited decreased level of endogenous jasmonic acid what indicated interaction between those two phytohormones at a low temperature. The study also demonstrated that in vitro culture, cold storage and ABA treatment had no effect on the flowering process of this species after acclimatization to ex vitro conditions.

The arbuscular mycorrhizal mycelium from barley differentially influences various defense parameters in the non-host sugar beet under co-cultivation.

The interactions between arbuscular mycorrhizal fungi (AMF) and non-host species are poorly studied. Particularly scarce is information on members of the Amaranthaceae/Chenopodiaceae family. Sugar beet (Beta vulgaris) plants were co-cultivated with a host species (Hordeum vulgare) in the presence (+AMF) or absence of Rhizophagus intraradices to explore the hypothesis that the presence of an active, pre-established AMF mycelium induces defense responses in the non-host species. Biomass of sugar beet did not respond to the +AMF treatment, while its root exudation of organic acids and phenolic acids was drastically decreased upon co-cultivation with +AMF barley. The most conspicuous effect was observed on a wide range of potential defense parameters being differentially influenced by the +AMF treatment in this non-host species. Antioxidant defense enzymes were activated and the level of endogenous jasmonic acid was elevated accompanied by nitric oxide accumulation and lignin deposition in the roots after long-term +AMF treatment. In contrast, significant reductions in the levels of endogenous salicylic acid and tissue concentration and exudation of phenolic acids indicated that AM fungus hyphae in the substrate did not induce a hypersensitive-type response in the sugar beet roots and downregulated certain chemical defenses. Our results imply that the fitness of this non-host species is not reduced when grown in the presence of an AMF mycelium because of balanced defense costs. Further studies should address the question of whether or not such modulation of defense pattern influences the pest resistance of sugar beet plants under field conditions.

Transcription factor LkWOX4 is involved in adventitious root development in Larix kaempferi.

WUSCHEL-related homeobox4 (WOX4) plays important roles in vascular formation and adventitious root (AR) development. Here, we cloned the WOX4 from the AR of Larix kaempferi, whose cDNA is 1452bp in length and encodes 483 amino acids. LkWOX4 is mainly expressed in the layer formation area of the stem at 10days after cutting and its expression levels in the middles and ends of the ARs were higher than that in the AR tips. The fused protein LkWOX4-GFP localized in the nucleus. The heterologous overexpression of LkWOX4 in 84K poplar significantly increased AR numbers and decreased AR lengths. In LkWOX4 plants, the endogenous jasmonic acid and abscisic acid contents significantly decreased in stems, while the auxin, jasmonic acid and abscisic acid contents significantly increased in ARs. RNA-Seq of those LkWOX4 overexpression poplar plants showed that the expression of plant hormone signaling genes (ARF2, ARF3, ARF7 and ARF18), rooting-related transcription factors (WOX5, LBD29 and SCR) and root development-related genes (CYCD3, GRF1 and TAA1) were affected. Moreover, we found that LkWOX4 interacts with LkPAT18, LkACBP6, and LkCIP7 using yeast two hybrid screening. Thus, we found LkWOX4 involves in the AR initiation and development, which might be regulated through the IAA, JA and ABA signaling pathways.

Impact of Soil Rhizobacteria Inoculation and Leaf-Chewing Insect Herbivory on Mentha piperita Leaf Secondary Metabolites.

Secondary metabolites commonly play important physiological roles in plants and can be modified quantitatively and qualitatively by exposure to biotic and abiotic interactions. Plant growth promoting rhizobacteria (PGPR) and herbivory induce systemic resistance. In the present study, we analyzed the induction of secondary metabolites in peppermint plants in response to chewing insect herbivory on PGPR-inoculated Mentha piperita plants. The secondary metabolites of M. piperita plants were increased when plants were inoculated with PGPR and also exposed to caterpillar herbivory. It was found that the total essential oil yield in inoculated plants with insect damage was ~2.6-fold higher than in controls. The yield was similar to that of plants either damaged by insects or inoculated, indicating that there was no synergism. The same trend was observed for phenolic compounds. In contrast, VOC emissions were significantly higher in plants infested by insects, independent of whether they were inoculated. Insect damaged plants had 5.5 times higher monoterpene emissions than control plants, and ~ 2-fold higher emissions than on PGPR-inoculated plants without insects. To gain a better understanding of how herbivory on PGPR-inoculated plants can cause an increase in secondary metabolites of peppermint, we examined changes in plant defense hormones in inoculated plants after herbivory. We found that the combination of both treatments increased the endogenous jasmonic and salicylic acid levels to the same extent as in plants only inoculated or only insect-damaged. Because different interactions can alter the phytochemistry of plants such as M. piperita, this topic is both ecologically and economically relevant.

Seed browning in pepper (Capsicum annuum L.) fruit during cold storage is inhibited by methyl jasmonate or induced by methyl salicylate

• Seed browning is a major chilling injury symptom in cold-stored pepper. • Seed browning was reduced by MeJA but induced by MeSA. • MeJA could inhibit seed browning by activating the JA signalling pathway. • MeJA could inhibit seed browning by increasing glutamate and galactinol content. Chilling injury in pepper ( Capsicum annuum L.) fruit during cold storage and market distribution results in quality loss. In the present study, seed browning, a major chilling injury symptom, was observed in pepper fruit stored at 2 °C, but not at 13 °C. To alleviate this symptom, we applied vapour treatments of 50 μM methyl jasmonate (MeJA) or 250 μM methyl salicylate (MeSA), or a combination of both, and investigated the effect of treatments on seed browning in pepper fruit during cold storage. When treated with 50 μM MeJA, seed browning was highly inhibited and endogenous jasmonic acid (JA) production was increased via earlier activation of JA synthesis-related genes. However, MeSA treatment induced more severe and faster seed browning than the other treatments by decreasing endogenous JA content and by increasing salicylic acid (SA) content. The content of glutamate, sucrose, and galactinol, which are well-known antioxidant metabolites against chilling stress, was higher in MeJA-treated pepper fruit than in MeSA-treated pepper fruit, suggesting the role of MeJA in reducing chilling injury. In conclusion, JA may play an important role in reducing low temperature-induced seed browning in pepper fruit and SA seems to be involved in inducing chilling sensitivity in pepper fruit.

Cyclophilin AtROC1S58F confers Arabidopsis cold tolerance by modulating jasmonic acid signaling and antioxidant metabolism

Cyclophilins (CYPs), a class of proteins with a conserved peptidyl-prolyl cis-trans isomerase domain, are widely involved in the regulation of plant growth and development, as well as in the response to abiotic stresses including cold. In our previous study, we identified an Arabidopsis gain-of-function mutant ROC1S58F with enhanced cold-tolerance and enhanced expression of jasmonic acid (JA) and oxidative stress responsive genes. Here, we show the underlying molecular mechanisms for the improved cold tolerance observed in the ROC1S58F mutant. Compared to the WT, the ROC1S58F mutant showed an increased survival rates and a reduced level of electrolyte leakage and endogenous JA content under the freezing treatment. Correspondingly, the JA biosynthesis genes (AtAOC1 and AtOPR3) and signaling genes (AtJAZ5, AtJAZ10 and AtMYB15) are down-regulated in the ROC1S58F mutant compared with the WT. Moreover, both the transcripts and activities of the ROS-scavenging enzymes (SOD/POD/MDHAR) increased in cold-stressed ROC1S58F mutant, which might mitigate the ROS-induced oxidative stress and contribute to the mutant freezing tolerance. Taken together, our findings indicate that AtROC1S58F confers Arabidopsis freezing tolerance by modulating JA signaling and antioxidant metabolism jointly. This research thus provides a molecular mechanism for AtROC1S58F-conferred freezing resistance in Arabidopsis and offers guidance for crop breeding towards an improved cold tolerance.

L-Isoleucine (Ile) Promotes Anthocyanin Accumulation in Apples

The functions of l-isoleucine (Ile) in anthocyanin biosynthesis were investigated in apple fruit. Whole trees (Malus × domestica Bokh.) were treated with Ile or n-propyl dihydrojasmonate (PDJ), which is a jasmonic acid (JA) analog, 20 and 30 days before harvest. Both Ile and PDJ treatments stimulated anthocyanin formation at 30 and 35 days after treatment (DAT). The expressions of MdUF3GT and MdMYB1 genes under the Ile and PDJ treatments were higher than those in the untreated control at 19 and 30 DAT. Endogenous JA and jasmonoyl-l-isoleucine (JA-Ile) concentrations in Ile- and PDJ- treated fruit were increased at 19 and 30 DAT. At 30 DAT, the Ile and PDJ treatments stimulated the expressions of MdJAR1, which is related to the conjugation of JA to Ile, and MdMYC2, which is a transcription factor in the JA response. Our study suggests that Ile can induce anthocyanin formation depending on the increase of JA-Ile production and the up-regulation of MdJAR1 and MdMYC2 in apples.

The expression characteristics of methyl jasmonate biosynthesis–related genes in Cymbidium faberi and influence of heterologous expression of CfJMT in Petunia hybrida

Cymbidium faberi Rolfe (Orchidaceae) is an herbaceous plant native to China, where it has a long history of cultivation owing to its beautiful flower pattern and floral fragrance. Previously, we conducted a transcriptome analysis of the flower and vegetative buds to elucidate the mechanisms of flower development in C. faberi. In the present study, we found nine secondary metabolic pathways through the KEGG pathway database that were related to the biosynthesis of methyl jasmonate (MeJA) and other volatile organic compounds. qRT-PCR was performed to analyze the expression levels of four key genes in the MeJA pathway. Among these, CfJMT (jasmonic acid carboxyl methyltransferase) had higher transcript levels in sepals, petals and labella than in other tissues. CfJMT was cloned from the petals of full-bloom flowers of C. faberi. The predicted CfJMT protein sequence contains conserved jasmonic acid methyl transferase-7 domains, indicating that it belongs to the SABATH protein family. The CfJMT coding sequence driven by the CaMV35S promoter was successfully transformed into Petunia hybrida through an Agrobacterium-mediated method. Although MeJA could not be detected in either wild-type or transgenic petunia plants, the leaves of the transgenic plants were smaller than those of wild-type plants and pollen development was abnormal. These results indicate that heterologous expression of CfJMT may change the levels of endogenous jasmonic acid and other hormones, but that the content of MeJA is not increased significantly by transformation with CfJMT alone. Thus, other related genes and regulation factors may play important roles in this process.

The WRKY transcription factor PlWRKY65 enhances the resistance of Paeonia lactiflora (herbaceous peony) to Alternaria tenuissima

In this study, the disease resistance gene PlWRKY65 was isolated from the leaves of Paeonia lactiflora and analyzed by bioinformatics methods, and the localization of the encoded protein was explored. Quantitative real-time PCR (qRT-PCR) was also used to explore the response of this gene to Alternaria tenuissima. The results showed that the gene sequence contained multiple cis-acting elements involved in the response to hormone signaling molecules belonging to the IIe subgroup of the WRKY family, and the encoded proteins were located in the nucleus. The PlWRKY65 gene has a positive regulatory effect on A. tenuissima infection. After silencing the PlWRKY65 gene via virus-induced gene silencing (VIGS), it was found that the gene-silenced plants were more sensitive to A. tenuissima infection than the wild plants, exhibiting more severe infection symptoms and different degrees of changes in the expression of the pathogenesis-related (PR) genes. In addition, we showed that the endogenous jasmonic acid (JA) content of P. lactiflora was increased in response to A. tenuissima infection, whereas the salicylic acid (SA) content decreased. After PlWRKY65 gene silencing, the levels of the two hormones changed accordingly, indicating that PlWRKY65, acting as a disease resistance-related transcriptional activator, exerts a regulatory effect on JA and SA signals. This study lays the foundation for functional research on WRKY genes in P. lactiflora and for the discovery of candidate disease resistance genes.

Elevated atmospheric CO2 suppresses jasmonate and silicon‐based defences without affecting herbivores

Abstract Elevated atmospheric CO2 (eCO2) not only increases plant growth but can also interfere with defence against insect herbivory through the disruption of the jasmonic acid (JA) pathway. Silicon (Si) plays an important role in plant stress tolerance and resistance to herbivory, particularly in grasses, many of which accumulate high amounts of Si. Activation of the JA pathway has been reported to stimulate Si uptake, while Si supplementation can alter both constitutive and induced phytohormone levels. A reduction in JA concentration under eCO2 has the potential to reduce Si uptake in plants. Using both Si supplemented (Si+) and control (Si−) plants (Brachypodium distachyon) grown under ambient (400 ppm) and elevated (640 ppm) CO2 concentrations, we tested how plant growth, foliar Si concentration and endogenous JA responded to methyl jasmonate (MeJA) application and the subsequent effects on insect herbivore performance (Helicoverpa armigera). Elevated CO2 reduced Si concentration by 19% and endogenous JA by 70% on average. MeJA significantly increased Si concentration in Si+ plants. Si+ plants had higher baseline JA levels compared to Si− plants under control conditions (i.e. no stress), however, when plants were chemically induced with MeJA, the JA response was on average 84% lower in Si+ plants compared to Si− plants. Plants without MeJA treatment showed the opposite response, that is, Si+ plants had higher baseline JA levels compared to Si− plants. Si significantly reduced herbivore consumption and growth rate. Despite eCO2 significantly reducing both Si and endogenous JA, no effect was seen on herbivores feeding on eCO2 plants. Collectively our results suggest that Si alters the JA response of plants. We show that JA induces Si uptake, however, Si then reduces the JA response of plants under induced stress conditions. However, predicted increases in CO2 levels within this century may significantly reduce Si‐based mechanical defences against herbivory via a reduction of endogenous JA. A free Plain Language Summary can be found within the Supporting Information of this article.

Effects of genotypes and explants on garlic callus production and endogenous hormones

High callus production is a feasible way to improve the propagation coefficient of garlic. It remains unknown how genotypes and explants affect garlic callus formation. In the present investigation, we found that there were significant differences in callus formation among garlic varieties. Tip explants were the best calli-producing source, and 91.05% of the explants from four varieties, on average, formed calli after 45 d of primary culturing. Upper leaf parts explants produced lower values. Among the different varieties and explant types, tip explants of variety T141 induced calli in the shortest time and had the greatest callus fresh weight at 45 d. An endogenous hormone contents analysis showed that auxins (indole-3-acetic acid and methyl indole-3-acetic acetate), cytokinins (trans-zeatin and dihydrozeatin), gibberellins4, 9,15,19,24 and 53, abscisic acid, jasmonic acid, jasmonoyl-L-isoleucine, and dihydrojasmonic acid were significantly greater in the tips than those in the upper leaf parts. High endogenous jasmonic acid content might play important roles in callus formation. These results will help us not only establish an efficient garlic callus induction protocol that can be applied to large-scale callus multiplication and regeneration, and to genetically improvement of garlic production, but also understand endogenous hormone roles in tissue/organ differentiation and dedifferentiation.

The transcription factor VaNAC17 from grapevine (Vitis amurensis) enhances drought tolerance by modulating jasmonic acid biosynthesis in transgenic Arabidopsis.

Expression of VaNAC17 improved drought tolerance in transgenic Arabidopsis by upregulating stress-responsive genes, modulating JA biosynthesis, and enhancing ROS scavenging. Water deficit severely affects the growth and development of plants such as grapevine (Vitis spp.). Members of the NAC (NAM, ATAF1/2, and CUC2) transcription factor (TF) family participate in drought-stress-induced signal transduction in plants, but little is known about the roles of NAC genes in drought tolerance in grapevine. Here, we explored the role of VaNAC17 in Vitis amurensis, a cold-hardy, drought-tolerant species of grapevine. VaNAC17 was strongly induced in grapevine by drought, exogenous abscisic acid (ABA), and methyl jasmonate (MeJA). A transient expression assay in yeast indicated that VaNAC17 functions as a transcriptional activator. Notably, heterologous expression of VaNAC17 in Arabidopsis thaliana enhanced drought tolerance. VaNAC17-expressing Arabidopsis plants showed decreased reactive oxygen species (ROS) accumulation compared to wild-type plants under drought conditions. RNA-seq analysis indicated that VaNAC17 expression increased the transcription of downstream stress-responsive genes after 5days of drought treatment, especially genes involved in jasmonic acid (JA) biosynthesis (such as LOX3, AOC1 and OPR3) and signaling (such as MYC2, JAZ1, VSP1 and CORI3) pathways. Endogenous JA levels increased in VaNAC17-OE plants under drought stress. Taken together, these results indicate that VaNAC17 plays a positive role in drought tolerance by modulating endogenous JA biosynthesis and ROS scavenging.