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Abstract
Plant responses to low temperature are tightly associated with defense responses. We previously characterized the chilling-sensitive mutant chs3-1 resulting from the activation of the Toll and interleukin 1 receptor-nucleotide binding-leucine-rich repeat (TIR-NB-LRR)-type resistance (R) protein harboring a C-terminal LIM (Lin-11, Isl-1 and Mec-3 domains) domain. Here we report the identification of a suppressor of chs3, ibr5-7 (indole-3-butyric acid response 5), which largely suppresses chilling-activated defense responses. IBR5 encodes a putative dual-specificity protein phosphatase. The accumulation of CHS3 protein at chilling temperatures is inhibited by the IBR5 mutation. Moreover, chs3-conferred defense phenotypes were synergistically suppressed by mutations in HSP90 and IBR5. Further analysis showed that IBR5, with holdase activity, physically associates with CHS3, HSP90 and SGT1b (Suppressor of the G2 allele of skp1) to form a complex that protects CHS3. In addition to the positive role of IBR5 in regulating CHS3, IBR5 is also involved in defense responses mediated by R genes, including SNC1 (Suppressor of npr1-1, Constitutive 1), RPS4 (Resistance to P. syringae 4) and RPM1 (Resistance to Pseudomonas syringae pv. maculicola 1). Thus, the results of the present study reveal a role for IBR5 in the regulation of multiple R protein-mediated defense responses.
Highlights
Plant growth and development are continuously affected by various environmental stresses, including low temperature and pathogen infection
We observed that the enhanced defense responses and cell death in the chs3-1 mutant are synergistically dependent on IBA RESPONSE5 (IBR5) and HSP90
IBR5 physically interacts with CHS3, forming a complex with SGT1b/ HSP90
Summary
Plant growth and development are continuously affected by various environmental stresses, including low temperature and pathogen infection. A recent study showed that low temperatures (10°C to 23°C) elevate R protein-mediated effectortriggered immunity (ETI), and higher temperatures (23°C to 32°C) lead to a shift in patterntriggered immunity (PTI) signaling in plants [9] These studies suggest that temperature largely affects the function of R proteins. A series of regulators of SNC1 were identified by screening suppressors and enhancers of snc, have been shown to regulate the chromatin, transcription and protein levels of SNC1 These proteins include E1 and E4 ligases, U-box proteins, acetyltransferases, RNA binding proteins, nuclear pore complex components [13,17,18,19,20,21,22]. These results suggest that SNC1 and/or other R proteins are regulated by multiple biological processes including nucleo-cytoplasmic trafficking, transcriptional reprogramming, RNA processing and protein modification
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