식물 GSK3-like kinase에 의해 조절되는 아마딜로계열 단백질의 기능에 관한 연구

Abstract

Plant GSK3-like kinases are key negative regulators of brassinosteroid (BR) signal transduction. Recently, based on newly identified substrates, it was known that GSK3-like kinases appeared to regulate diverse developments including xylem, roots, and stomatal cells. I screened a novel protein carrying Armadillo (Arm) repeat motifs as a substrate of GSK3-like kinase BIN2 and named as BITA1 (BIN2-interacting Armadillo 1). BITA1 interacted with BIN2 in vitro and in vivo. In vitro kinase assay indicated that BITA1 is phosphorylated by BIN2. Like BIN2-YFP, BITA1-YFP localized at both nucleus and cytoplasm. When expression pattern of BITA1 was analyzed by BITA1 promoter-GUS transgenic Arabidopsis, BITA1 was predominantly expressed in cotyledons and roots. Interestingly, BITA1 is highly expressed in primary roots but not in lateral root primordium. Consistently, transgenic plant overexpressing BITA1-YFP showed reduced number of lateral root compared with that of wild-type plant. In addition, the bita1 knockdown mutant produced increased the number of lateral root (LR), suggesting that BITA1 negatively regulates lateral root development. This phenotype was suppressed by IAA treatment which promotes lateral root formation. In addition, BITA1-YFP plants are hypersensitive to Bikinin (GSK3-like kinase BIN2 inhibitor) that inhibits lateral root development. BITA1-YFP level was dramatically accumulated by Bikinin and MG132 treatment. This suggests that BITA1 is destabilized by BIN2-dependent phosphorylation, resulting in inhibition of lateral root development. Taken together, I demonstrated that an Armadillo-repeat protein, BITA1, is a negative regulator in lateral root formation and its activity is suppressed by BIN2 phosphorylation.