BRL1 and BRL3 are novel brassinosteroid receptors that function in vascular differentiation in Arabidopsis

Plant steroid hormones, brassinosteroids (BRs), are perceived by the plasma membrane-localized leucine-rich-repeat-receptor kinase BRI1. Based on sequence similarity, we have identified three members of the BRI1 family, named BRL1, BRL2 and BRL3. BRL1 and BRL3, but not BRL2, encode functional BR receptors that bind brassinolide, the most active BR, with high affinity. In agreement, only BRL1 and BRL3 can rescue bri1 mutants when expressed under the control of the BRI1 promoter. While BRI1 is ubiquitously expressed in growing cells, the expression of BRL1 and BRL3 is restricted to non-overlapping subsets of vascular cells. Loss-of-function of brl1 causes abnormal phloem:xylem differentiation ratios and enhances the vascular defects of a weak bri1 mutant. bri1 brl1 brl3 triple mutants enhance bri1 dwarfism and also exhibit abnormal vascular differentiation. Thus, Arabidopsis contains a small number of BR receptors that have specific functions in cell growth and vascular differentiation.Fil: Caño Delgado, Ana. Salk Institute. Plant Biology Laboratory; Estados Unidos. Howard Hughes Medical Institute; Estados UnidosFil: Yin, Yanhai. Howard Hughes Medical Institute; Estados Unidos. Salk Institute. Plant Biology Laboratory; Estados UnidosFil: Yu, Cong. University of Michigan; Estados UnidosFil: Vafeados, Dionne. Howard Hughes Medical Institute; Estados Unidos. Salk Institute. Plant Biology Laboratory; Estados UnidosFil: Mora Garcia, Santiago. Howard Hughes Medical Institute; Estados Unidos. Salk Institute. Plant Biology Laboratory; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Cheng, Jin Chen. University of Michigan; Estados UnidosFil: Nam, Kyoung Hee. University of Michigan; Estados UnidosFil: Li, Jianming. University of Michigan; Estados UnidosFil: Chory, Joanne. Salk Institute. Plant Biology Laboratory; Estados Unidos. Howard Hughes Medical Institute; Estados Unido