Sreeramulu S, Mostizky Y, Sunitha S, Shani E, Nahum H, Salomon D, Ben Hayun L, Gruetter C, Rauh D, Ori N, Sessa G

Arabidopsis thaliana Brassinosteroid Signaling Kinases (BSKs) constitute a receptor-like cytoplasmic kinase subfamily (RLCK-XII) of 12 members. Previous analysis demonstrated a positive role for BSK1 and BSK3 in the initial steps of brassinosteroid (BR) signal transduction. To investigate the function of BSKs in plant growth and BR signaling, we characterized T-DNA ...

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insertion lines within 8 BSK genes (BSK1 to BSK8) and multiple mutant combinations. Simultaneous elimination of three BSKs caused alterations in growth and in the BR response, while most severe phenotypes were observed in the bsk3,4,7,8 quadruple and bsk3,4,6,7,8 pentuple mutants, which displayed reduced rosette size, leaf curling, and enhanced leaf inclination. In addition, upon treatment with 24-epibrassinolide, these mutants showed reduced hypocotyl elongation, enhanced root growth, and alteration in the expression of BR-responsive genes. Some mutant combinations also showed antagonistic interactions. In support of a redundant function in BR signaling, multiple BSKs interacted in vivo with the BR receptor BRI1 and served in vitro as its phosphorylation substrates. The BIN2 and BIL2 GSK3-like kinases, which are negative regulators of BR signaling, interacted in vivo with BSKs and phosphorylated them in vitro, likely at different sites than BRI1. This study demonstrates redundant biological functions for BSKs and suggests a novel regulatory link between BSKs and GSK3-like kinases. © 2013 The Authors. The Plant Journal © 2013 Blackwell Publishing Ltd.

Date: Mar. 15, 2013

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