Knock-down of protein phosphatase 2a subunit b'7 promotes phosphorylation of calreticulin 1 in arabidopsis thaliana

Abstract

Controlled protein dephosphorylation by protein phosphatase 2a (PP2a) regulates diverse signaling events in plants. recently, we showed that a specific B'7 regulatory subunit of PP2a mediates basal repression of immune reactions in Arabidopsis thaliana. Knock-down pp2a-b'y mutants display constitutive defense reactions and premature yellowing conditionally under moderate light intensity. here we show that knock-down of PP2A-B'y renders CaLrEtiCuLiN 1 (Crt1) highly phosphorylated. Calreticulins are Er-resident chaperonins that operate in the unfolded protein response to prevent Er-stress, components of which are differentially regulated at mrNa level in pp2a-b'y leaves. We speculate that in dephosphorylated state, Crt1 promotes the degradation of unfolded proteins in Er. our findings suggest that in wild type plants, dephosphorylation of Crt1 is mediated by PP2a-B'7 dependent signaling effects. in pp2a-b'y, strong phosphorylation of Crt1 may partially imbalance the quality control of protein folding, thereby eliciting Er-stress and premature yellowing in leaves. ©2011 Landes Bioscience.