A key ABA biosynthetic gene OsNCED3 is a positive regulator in resistance to Nilaparvata lugens in Oryza sativa.

The gene encoding 9-cis-epoxycarotenoid dioxygenase 3 (NCED3) functions in abscisic acid (ABA) biosynthesis, plant growth and development, and tolerance to adverse temperatures, drought and saline conditions. In this study, three rice lines were used to explore the function of OsNCED3, these included an OsNCED3-overexpressing line (OsNCED3-OE), a knockdown line (osnced3-RNAi) and wild-type rice (WT). These rice lines were infested with the brown plant hopper (BPH; Nilaparvata lugens) and examined for physiological and biochemical changes, hormone content, and defense gene expression. The results showed that OsNCED3 activated rice defense mechanisms, which led to an increased defense enzyme activity of superoxide dismutase, peroxidase, and polyphenol oxidase. The overexpression of OsNCED3 decreased the number of planthoppers and reduced oviposition and BPH hatching rates. Furthermore, the overexpression of OsNCED3 increased the concentrations of jasmonic acid, jasmonyl-isoleucine and ABA relative to WT rice and the osnced3-RNAi line. These results indicate that OsNCED3 improved the stress tolerance in rice and support a role for both jasmonates and ABA as defense compounds in the rice-BPH interaction.

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.

Exogenous plant hormones alleviate As stress by regulating antioxidant defense system in Oryza sativa L.

Plant hormones play essential roles in plant growth regulation and resistance to environmental pressure. A hydroponic experiment was conducted using Zhongjiazao 17 rice to explore the effects of exogenous plant hormones on antioxidant response and As accumulation in rice under As stress. Melatonin (MT), 2,4-epibrassinolide (EBL), and jasmonic acid (JA) reduced the As content in seedlings significantly by 13.4% (MT)-32.5% (EBL) under 5 µM As stress. Three hormones increased superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities, and glutathione (GSH) content significantly (2.2%-82.9%) in 5 µM As stress condition, whereas the levels of H2O2 and malondialdehyde (MDA) were reduced significantly (32.3%-78.1%). Plant hormone addition reduced the As content in seedlings significantly by 18.2% (JA)-33.3% (MT) under 25 µM As stress. SOD, POD, and CAT activities and GSH content in seedlings increased significantly (5.6-90.4%) with three hormones addition in 25 µM As stress, whereas the levels of H2O2, O2˙¯, and MDA reduced significantly (20.9-73.0%). Staining with 2',7'-dichlorodihydrofluorescein diacetate and nitroblue tetrazolium showed that green fluorescence and blue spots decreased gradually in hormone-treated seedlings, further confirming that the exogenous addition of hormones weakened the oxidative stress of As to seedlings. Oxidative damage by As stress was reduced more by EBL than by the other hormones MT or JA. Totally, exogenous plant hormone can alleviate As stress in rice by activating enzyme activity of antioxidant defense system and scavenging reactive oxygen species, thus reducing oxidative damage and As accumulation in rice seedlings.

A Novel Guanine Elicitor Stimulates Immunity in Arabidopsis and Rice by Ethylene and Jasmonic Acid Signaling Pathways.

Rice sheath blight (ShB) caused by Rhizoctonia solani is one of the most destructive diseases in rice. Fungicides are widely used to control ShB in agriculture. However, decades of excessive traditional fungicide use have led to environmental pollution and increased pathogen resistance. Generally, plant elicitors are regarded as environmentally friendly biological pesticides that enhance plant disease resistance by triggering plant immunity. Previously, we identified that the plant immune inducer ZhiNengCong (ZNC), a crude extract of the endophyte, has high activity and a strong ability to protect plants against pathogens. Here, we further found that guanine, which had a significant effect on inducing plant resistance to pathogens, might be an active component of ZNC. In our study, guanine activated bursts of reactive oxygen species, callose deposition and mitogen-activated protein kinase phosphorylation. Moreover, guanine-induced plant resistance to pathogens depends on ethylene and jasmonic acid but is independent of the salicylic acid signaling pathway. Most importantly, guanine functions as a new plant elicitor with broad-spectrum resistance to activate plant immunity, providing an efficient and environmentally friendly biological elicitor for bacterial and fungal disease biocontrol.

Functional analysis of hot pepper ethylene responsive factor 1A in plant defense.

Ethylene-responsive factors play important roles in the biotic and abiotic stresses. Only some ERF genes from Capsicum annuum have been characterized. In the study, the CaERF1A gene is characterized in response to biotic stress. CaERF1A transcripts were induced by various plant defense-related hormone treatments. Knockdown of CaERF1A in hot pepper plants are negatively affected Tobacco mosaic virus-P0-mediated hypersensitive response cell death, resulting in reduced gene expression of pathogenesis-related genes and ethylene and jasmonic acid synthesis-related gene. Overexpressing CaERF1A transgenic plants show enhanced resistance to fungal pathogen via regulating ethylene and jasmonic acid synthesis-related gene expression. Thus, CaERF1A is a positive regulator of plant defense by modulating ethylene and jasmonic acid synthesis-related gene expressions.

Oxathiapiprolin, a Novel Chemical Inducer Activates the Plant Disease Resistance.

Oxathiapiprolin was developed as a specific plant pathogenic oomycete inhibitor, previously shown to have highly curative and protective activities against the pepper Phytophthora blight disease under field and greenhouse tests. Therefore, it was hypothesized that oxathiapiprolin might potentially activate the plant disease resistance against pathogen infections. This study investigated the potential and related mechanism of oxathiapiprolin to activate the plant disease resistance using the bacterium Pseudomonas syringae pv tomato (Pst) and plant Arabidopsis interaction as the targeted system. Our results showed that oxathiapiprolin could activate the plant disease resistance against Pst DC3000, a non-target pathogen of oxathiapiprolin, in Arabidopsis, tobacco, and tomato plants. Our results also showed the enhanced callose deposition and H2O2 accumulation in the oxathiapiprolin-treated Arabidopsis under the induction of flg22 as the pathogen-associated molecular pattern (PAMP) treatment. Furthermore, increased levels of free salicylic acid (SA) and jasmonic acid (JA) were detected in the oxathiapiprolin-treated Arabidopsis plants compared to the mock-treated ones under the challenge of Pst DC3000. Besides, the gene expression results confirmed that at 24 h after the infiltration with Pst DC3000, the oxathiapiprolin-treated Arabidopsis plants had upregulated expression levels of the respiratory burst oxidase homolog D (RBOHD), JA-responsive gene (PDF1.2), and SA-responsive genes (PR1, PR2, and PR5) compared to the control. Taken together, oxathiapiprolin is identified as a novel chemical inducer which activates the plant disease resistance against Pst DC3000 by enhancing the callose deposition, H2O2 accumulation, and hormone SA and JA production.

Herbivore-specific plant volatiles prime neighboring plants for nonspecific defense responses.

Plants produce species-specific herbivore-induced plant volatiles (HIPVs) after damage. We tested the hypothesis that herbivore-specific HIPVs prime neighboring plants to induce defenses specific to the priming herbivore. Since Manduca sexta (specialist) and Heliothis virescens (generalist) herbivory induced unique HIPV profiles in Nicotiana benthamiana, we used these HIPVs to prime receiver plants for defense responses to simulated herbivory (mechanical wounding and herbivore regurgitant application). Jasmonic acid (JA) accumulations and emitted volatile profiles were monitored as representative defense responses since JA is the major plant hormone involved in wound and defense signaling and HIPVs have been implicated as signals in tritrophic interactions. Herbivore species-specific HIPVs primed neighboring plants, which produced 2 to 4 times more volatiles and JA after simulated herbivory when compared to similarly treated constitutive volatile-exposed plants. However, HIPV-exposed plants accumulated similar amounts of volatiles and JA independent of the combination of priming or challenging herbivore. Furthermore, volatile profiles emitted by primed plants depended only on the challenging herbivore species but not on the species-specific HIPV profile of damaged emitter plants. This suggests that feeding by either herbivore species primed neighboring plants for increased HIPV emissions specific to the subsequently attacking herbivore and is probably controlled by JA.

Triggering a false alarm: wounding mimics prey capture in the carnivorous Venus flytrap (Dionaea muscipula).

In the carnivorous plant Venus flytrap (Dionaea muscipula), the sequence of events after prey capture resembles the well-known plant defence signalling pathway in response to pathogen or herbivore attack. Here, we used wounding to mimic prey capture to show the similarities and differences between botanical carnivory and plant defence mechanisms. We monitored movement, electrical signalling, jasmonate accumulation and digestive enzyme secretion in local and distal (systemic) traps in response to prey capture, the mechanical stimulation of trigger hairs and wounding. The Venus flytrap cannot discriminate between wounding and mechanical trigger hair stimulation. Both induced the same action potentials, rapid trap closure, hermetic trap sealing, the accumulation of jasmonic acid (JA) and its isoleucine conjugate (JA-Ile), and the secretion of proteases (aspartic and cysteine proteases), phosphatases and type I chitinase. The jasmonate accumulation and enzyme secretion were confined to the local traps, to which the stimulus was applied, which correlates with the propagation of electrical signals and the absence of a systemic response in the Venus flytrap. In contrast to plant defence mechanisms, the absence of a systemic response in carnivorous plant may represent a resource-saving strategy. During prey capture, it could be quite expensive to produce digestive enzymes in the traps on the plant without prey.

Shifting from priming of salicylic acid- to jasmonic acid-regulated defences by Trichoderma protects tomato against the root knot nematode Meloidogyne incognita.

Beneficial root endophytes such as Trichoderma spp. can reduce infections by parasitic nematodes through triggering host defences. Little is currently known about the complex hormone signalling underlying the induction of resistance. In this study, we investigated whether Trichoderma modulates the hormone signalling network in the host to induce resistance to nematodes. We investigated the role and the timing of the jasmonic acid (JA)- and salicylic acid (SA)-regulated defensive pathways in Trichoderma-induced resistance to the root knot nematode Meloidogyne incognita. A split-root system of tomato (Solanum lycopersicum) was used to study local and systemic induced defences by analysing nematode performance, defence gene expression, responsiveness to exogenous hormone application, and dependence on SA and JA signalling of Trichoderma-induced resistance. Root colonization by Trichoderma impeded nematode performance both locally and systemically at multiple stages of the parasitism, that is, invasion, galling and reproduction. First, Trichoderma primed SA-regulated defences, which limited nematode root invasion. Then, Trichoderma enhanced JA-regulated defences, thereby antagonizing the deregulation of JA-dependent immunity by the nematodes, which compromised galling and fecundity. Our results show that Trichoderma primes SA- and JA-dependent defences in roots, and that the priming of responsiveness to these hormones upon nematode attack is plastic and adaptive to the parasitism stage.

The rapidly evolving associations among herbivore associated elicitor-induced phytohormones in Nicotiana.

In response to herbivore attack, plants perceive herbivore associated elicitors (HAE) and rapidly accumulate jasmonic acid (JA) and other phytohormones, which interact in complex ways, such as the crosstalk between JA and salicylic acid (SA). Although recent studies have shown that HAE-induced individual phytohormones can be highly specific among closely related species, it remains unclear how conserved and specific the relationships among HAE-induced phytohormones are. Here we analyzed the correlations among 4 different phytohormones, JA, JA-isoleucine (JA-Ile), SA, and abscisic acid (ABA) in 6 closely related Nicotiana species that were induced by 3 different HAEs. Our results showed that while no clear association between ABA and other phytohormones were found, the positive association between JA and JA-Ile is mostly conserved among closely related Nicotiana species. Interestingly, the association between JA and SA are highly variable and can be regulated by different HAEs.

Scopoletin is a phytoalexin against Alternaria alternata in wild tobacco dependent on jasmonate signalling.

Alternaria alternata (tobacco pathotype) is a necrotrophic fungus causing severe losses in Nicotiana species by infection of mature leaves. Similar to what has been observed in cultivated tobacco, N. tabacum, young leaves of wild tobacco, N. attenuata, were more resistant to A. alternata than mature leaves, and this was correlated with stronger blue fluorescence induced after infection. However, the nature of the fluorescence-emitting compound, its role in defence, and its regulation were not clear. Silencing feruloyl-CoA 6'-hydroxylase 1 (F6'H1), the gene encoding the key enzyme for scopoletin biosynthesis, by virus-induced gene silencing (VIGS) revealed that the blue fluorescence was mainly emitted by scopoletin and its ß-glycoside form, scopolin. Further analysis showed that scopoletin exhibited strong antifungal activity against A. alternata in vitro and in vivo. Importantly, jasmonic acid (JA) levels were highly elicited in young leaves but much less in mature leaves after infection; and fungus-elicited scopoletin was absent in JA-deficient plants, but was largely restored with methyl jasmonate treatments. Consistent with this, plants strongly impaired in JA biosynthesis and perception were highly susceptible to A. alternata in the same way scopoletin/scopolin-depleted VIGS F6'H1 plants. Furthermore, silencing MYC2, a master regulator of most JA responses, reduced A. alternata-induced NaF6'H1 transcripts and scopoletin. Thus, it is concluded that JA signalling is activated in N. attenuata leaves after infection, which subsequently regulates scopoletin biosynthesis for the defence against A. alternata partly through MYC2, and higher levels of scopoletin accumulated in young leaves account for their strong resistance.

Leaf-herbivore attack reduces carbon reserves and regrowth from the roots via jasmonate and auxin signaling.

Herbivore attack leads to resource conflicts between plant defensive strategies. Photoassimilates are required for defensive compounds and carbon storage below ground and may therefore be depleted or enriched in the roots of herbivore-defoliated plants. The potential role of belowground tissues as mediators of induced tolerance-defense trade-offs is unknown. We evaluated signaling and carbohydrate dynamics in the roots of Nicotiana attenuata following Manduca sexta attack. Experimental and natural genetic variability was exploited to link the observed metabolite patterns to plant tolerance and resistance. Leaf-herbivore attack decreased sugar and starch concentrations in the roots and reduced regrowth from the rootstock and flower production in the glasshouse and the field. Leaf-derived jasmonates were identified as major regulators of this root-mediated resource-based trade-off: lower jasmonate levels were associated with decreased defense, increased carbohydrate levels and improved regrowth from the rootstock. Application and transport inhibition experiments, in combination with silencing of the sucrose non-fermenting (SNF) -related kinase GAL83, indicated that auxins may act as additional signals that regulate regrowth patterns. In conclusion, our study shows that the ability to mobilize defenses has a hidden resource-based cost below ground that constrains defoliation tolerance. Jasmonate- and auxin-dependent mechanisms may lead to divergent defensive plant strategies against herbivores in nature.