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Summary: Plants have evolved an array of responses that provide them with protection from attack by microorganisms and other predators. Many of these mechanisms depend upon interactions between the plant hormones jasmonate (JA) and ethylene (ET). However, the molecular basis of these interactions is insufficiently understood.Gene expression and physiological assays with mutants were performed to investigate the role of Arabidopsis BIG gene in stress responses.BIG transcription is downregulated by methyl JA (MeJA), necrotrophic infection or mechanical injury. BIG deficiency promotes JA‐dependent gene induction, increases JA production but restricts the accumulation of both ET and salicylic acid. JA‐induced anthocyanin accumulation and chlorophyll degradation are enhanced and stomatal immunity is impaired by BIG disruption. Bacteria‐ and lipopolysaccaride (LPS)‐induced stomatal closure is reduced in BIG gene mutants, which are hyper‐susceptible to microbial pathogens with different lifestyles, but these mutants are less attractive to phytophagous insects.Our results indicate that BIG negatively and positively regulate the MYC2 and ERF1 arms of the JA signalling pathway. BIG warrants recognition as a new and distinct regulator that regulates JA responses, the synergistic interactions of JA and ET, and other hormonal interactions that reconcile the growth and defense dilemma in Arabidopsis. [ABSTRACT FROM AUTHOR]

Summary: Auxin gradients are sustained by series of influx and efflux carriers whose subcellular localization is sensitive to both exogenous and endogenous factors. Recently the localization of the Arabidopsis thaliana auxin efflux carrier PIN‐FORMED (PIN) 6 was reported to be tissue‐specific and regulated through unknown mechanisms. Here, we used genetic, molecular and pharmacological approaches to characterize the molecular mechanism(s) controlling the subcellular localization of PIN6. PIN6 localizes to endomembrane domains in tissues with low PIN6 expression levels such as roots, but localizes at the plasma membrane (PM) in tissues with increased PIN6 expression such as the inflorescence stem and nectary glands. We provide evidence that this dual localization is controlled by PIN6 phosphorylation and demonstrate that PIN6 is phosphorylated by mitogen‐activated protein kinases (MAPKs) MPK4 and MPK6. The analysis of transgenic plants expressing PIN6 at PM or in endomembrane domains reveals that PIN6 subcellular localization is critical for Arabidopsis inflorescence stem elongation post‐flowering (bolting). In line with a role for PIN6 in plant bolting, inflorescence stems elongate faster in pin6 mutant plants than in wild‐type plants. We propose that PIN6 subcellular localization is under the control of developmental signals acting on tissue‐specific determinants controlling PIN6‐expression levels and PIN6 phosphorylation. [ABSTRACT FROM AUTHOR]

* Systemin (SYS), an octadecapeptide hormone processed from a 200-amino-acid precursor (prosystemin, PS), plays a central role in the systemic activation of defense genes in tomato in response to herbivore and pathogen attacks. However, whether PS mRNA is transferable and its role in systemic defense responses remain unknown. * We created the transgenic tomato PS gene tagged with the green fluorescent protein (PS-GFP) using a shoot- or root-specific promoter, and the constitutive 35S promoter in Arabidopsis. Subcellular localization of PS-/SYS-GFP was observed using confocal laser scanning microscopy and gene transcripts were determined using quantitative real-time PCR. * In Arabidopsis, PS protein can be processed and SYS is secreted. Shoot-/root-specific expression of PS-GFP in Arabidopsis, and grafting experiments, revealed that the PS mRNA moves in a bi-directional manner. We also found that ectopic expression of PS improves Arabidopsis resistance to the necrotrophic fungus Botrytis cinerea, consistent with substantial upregulation of the transcript levels of specific pathogen-responsive genes. * Our results provide novel insights into the multifaceted mechanism of SYS signaling transport and its potential application in genetic engineering for increasing pathogen resistance across diverse plant families. [ABSTRACT FROM AUTHOR]

Summary Soil nitrogen (N) significantly influences the interaction between plants and pathogens, yet its impact on host defenses and pathogen strategies via alterations in plant metabolism remains unclear. Through metabolic and genetic studies, this research demonstrates that high‐N‐input exacerbates tomato bacterial wilt by altering γ‐aminobutyric acid (GABA) metabolism of host plants. Under high‐N conditions, the nitrate sensor NIN‐like protein 7 (SlNLP7) promotes the glutamate decarboxylase 2/4 (SlGAD2/4) transcription and GABA synthesis by directly binding to the promoters of SlGAD2/4. The tomato plants with enhanced GABA levels showed stronger immune responses but remained susceptible to Ralstonia solanacearum. This led to the discovery that GABA produced by the host actually heightens the pathogen's virulence. We identified the R. solanacearum LysR‐type transcriptional regulator OxyR protein, which senses host‐derived GABA and, upon interaction, triggers a response involving protein dimerization that enhances the pathogen's oxidative stress tolerance by activating the expression of catalase (katE/katGa). These findings reveal GABA's dual role in activating host immunity and enhancing pathogen tolerance to oxidative stress, highlighting the complex relationship between tomato plants and R. solanacearum, influenced by soil N status. [ABSTRACT FROM AUTHOR]

Recent studies on plants genetically modified in jasmonic acid (JA) signalling support the hypothesis that the jasmonate family of oxylipins plays an important role in mediating direct and indirect plant defences. However, the interaction of two modes of defence in tritrophic systems is largely unknown. In this study, we examined the preference and performance of a herbivorous leafminer (Liriomyza huidobrensis) and its parasitic wasp (Opius dissitus) on three tomato genotypes: a wild-type (WT) plant, a JA biosynthesis (spr2) mutant, and a JA-overexpression 35S::prosys plant. Their proteinase inhibitor production and volatile emission were used as direct and indirect defence factors to evaluate the responses of leafminers and parasitoids. Here, we show that although spr2 mutant plants are compromised in direct defence against the larval leafminers and in attracting parasitoids, they are less attractive to adult flies compared with WT plants. Moreover, in comparison to other genotypes, the 35S::prosys plant displays greater direct and constitutive indirect defences, but reduced success of parasitism by parasitoids. Taken together, these results suggest that there are distinguished ecological trade-offs between JA-dependent direct and indirect defences in genetically modified plants whose fitness should be assessed in tritrophic systems and under natural conditions., (© The Authors (2010). Journal compilation © New Phytologist Trust (2010).)