| As a group of important plant hormones,brassinosteroids(BRs)are involved in a wide range of plant growth and developmental processes.At the cell surface,BRs bind to the BRI1/BAK1 receptor/co-receptor complex.The signal can then transduce to the downstream components via reversible phosphorylation and dephosphorylation.Most studies on the point mutants in the Arabidopsis BRI1 kinase domain illustrated the essential roles of the kinase activity in BR signaling pathway.The mutants all show obvious BR defective phenotypes including extreme dwarfed statues,curly leaves,delayed blossom and male sterility.One allele of BRI1,a point mutant bri1-301,which shows a moderate BR defective phenotype and a reduced response to BRs under normal growth conditions.It has been reported the bri1-301 mutant is in the kinase domain.In vitro assay indicated that the kinase domain of bri1-301 does not show any kinase activity.Based on all the previous studies,the weak phenotype of bri1-301 is inconsistent with the kinase activity.Therefore,in order to study the kinase activity of bril-301,we detected the phosphorylation levels of BRI1 and BAK1.And we plan to estimate the significance of BRI1 kinase activity via studying the function of bri1-301.ELH1 is a response factor of BR signaling pathway in Arabidopsis.It is regulated by several key plant hormones,such as BRs,auxins,and GA.Our results demostrated that over-expression of ELH1 in wild type Arabidopsis showed an excessive Auxin biosynthesis phenotypes.And when ELH1 was over-expressed in bri1-5,the BR receptor mutant,the transgenic plants showed an obvious excessive gibberellin biosynthesis phenotype.Yeast two-hybrid results indicated that ELH1 can interact with RACK1 family proteins.We also proved that ELH1 located both on the cytomembrane and cytoplasm.According to the results we speculate that via a scaffold protein RACK1,ELH1 can interact with some hormone receptors to regulate auxin,BR,and gibberellin signaling pathways. |
