Abstract
A novel calmodulin-binding protein gene was identified by activation tagging of Lotus japonicus. We report on the functional analysis of two orthologous genes of Arabidopsis thaliana, designated brassinosteroid positive regulators (BPRs). In the ectopic overexpressor of BPR1, the leaf blades and petioles were elongated. The shortened leaf blade and petiole phenotypes of bpr1 knockout mutant were restored by exogenously applied brassinolide. Ectopic overexpression of BPR2 caused the epinasty of rosette leaves. Semi-quantitative RT-PCR analyses of the brassinosteroid biosynthetic genes using the transformants of the two genes suggested that BPR1 and BPR2 regulate the expression of different sets of biosynthetic genes. Histochemical analysis of the BPR1::GUS and BPR2::GUS expression revealed that BPR1 and BPR2 are expressed in different tissues and organs. BPR1-GFP and BPR2-GFP fusion proteins were localized to cell nuclei and plastids, respectively. These results suggest that BPR1 and BPR2 participate in spatial and temporal regulation of brassinosteroid biosynthesis.
