A non canonical subtilase attenuates the transcriptional activation of defence responses in <i>Arabidopsis thaliana</i>.

Abstract

Proteases play crucial physiological functions in all organisms by controlling the lifetime of proteins. Here, we identified an atypical protease of the subtilase family [SBT5.2(b)] that attenuates the transcriptional activation of plant defence independently of its protease activity. The <i>SBT5.2</i> gene produces two distinct transcripts encoding a canonical secreted subtilase [SBT5.2(a)] and an intracellular protein [SBT5.2(b)]. Concomitant to <i>SBT5.2(a)</i> downregulation, <i>SBT5.2(b)</i> expression is induced after bacterial inoculation. SBT5.2(b) localizes to endosomes where it interacts with and retains the defence-related transcription factor MYB30. Nuclear exclusion of MYB30 results in its reduced transcriptional activation and, thus, suppressed resistance. <i>sbt5.2</i> mutants, with abolished <i>SBT5.2(a)</i> and <i>SBT5.2(b)</i> expression, display enhanced defence that is suppressed in a <i>myb30</i> mutant background. Moreover, overexpression of SBT5.2(b), but not SBT5.2(a), in <i>sbt5.2</i> plants reverts the phenotypes displayed by <i>sbt5.2</i> mutants. Overall, we uncover a regulatory mode of the transcriptional activation of defence responses previously undescribed in eukaryotes.