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SUMMARY: The secretory pathway is essential for plant immunity, delivering diverse antimicrobial molecules into the extracellular space. Arabidopsis thaliana soluble N‐ethylmaleimide‐sensitive‐factor attachment protein receptor SNAP33 is a key actor of this process. The snap33 mutant displays dwarfism and necrotic lesions, however the molecular determinants of its macroscopic phenotypes remain elusive. Here, we isolated several new snap33 mutants that exhibited constitutive cell death and H2O2 accumulation, further defining snap33 as an autoimmune mutant. We then carried out quantitative transcriptomic and proteomic analyses showing that numerous defense transcripts and proteins were up‐regulated in the snap33 mutant, among which genes/proteins involved in defense hormone, pattern‐triggered immunity, and nucleotide‐binding domain leucine‐rich‐repeat receptor signaling. qRT‐PCR analyses and hormone dosages supported these results. Furthermore, genetic analyses elucidated the diverse contributions of the main defense hormones and some nucleotide‐binding domain leucine‐rich‐repeat receptor signaling actors in the establishment of the snap33 phenotype, emphasizing the preponderant role of salicylic acid over other defense phytohormones. Moreover, the accumulation of pattern‐triggered immunity and nucleotide‐binding domain leucine‐rich‐repeat receptor signaling proteins in the snap33 mutant was confirmed by immunoblotting analyses and further shown to be salicylic acid‐dependent. Collectively, this study unveiled molecular determinants underlying the Arabidopsis snap33 mutant phenotype and brought new insights into autoimmunity signaling. Significance Statement: SNAP33 is a key actor of secretion and the snap33 mutant exhibits dwarfism and necrotic lesions. The snap33 mutant is here further defined as an autoimmune mutant and molecular determinants of its macroscopic phenotypes are unveiled. [ABSTRACT FROM AUTHOR]

Abscisic acid ( ABA) is a major phytohormone involved in important stress-related and developmental plant processes. Recent phosphoproteomic analyses revealed a large set of ABA-triggered phosphoproteins as putative mitogen-activated protein kinase ( MAPK) targets, although the evidence for MAPKs involved in ABA signalling is still scarce. Here, we identified and reconstituted in vivo a complete ABA-activated MAPK cascade, composed of the MAP3Ks MAP3K17/18, the MAP2K MKK3 and the four C group MAPKs MPK1/2/7/14. In planta, we show that ABA activation of MPK7 is blocked in mkk3-1 and map3k17mapk3k18 plants. Coherently, both mutants exhibit hypersensitivity to ABA and altered expression of a set of ABA-dependent genes. A genetic analysis further reveals that this MAPK cascade is activated by the PYR/ PYL/ RCAR-Sn RK2- PP2C ABA core signalling module through protein synthesis of the MAP3Ks, unveiling an atypical mechanism for MAPK activation in eukaryotes. Our work provides evidence for a role of an ABA-induced MAPK pathway in plant stress signalling. [ABSTRACT FROM AUTHOR]

Examines the characterization of anionic channel in hypocotyl cells of Arabidopsis thaliana. Need of cytosolic adenosine triphosphate for the activation of the channel; Inhibition of the current by staurosporin; Ability of the channel to mediate anion efflux.