6). This result indicates
that the W444R substitution has no effect on the OsBRI1 subcellular localization. Brassinosteroids (BRs) are a class of steroid compounds involved in diverse biological processes during plant growth and development. Dasatinib mouse Here we have reported a classic semi-dwarf and erect-leaf rice mutant gsor300084. It belongs to the d6-type dwarf mutants, in which internode elongation was severely inhibited except for the uppermost internode. The gsor300084 mutant was shown to be related to BR and was less sensitive to BRs by assays of coleoptile elongation, root growth inhibition, and lamina joint inclination in the presence of exogenous BL. All these results indicate that gsor300084 is a BR-insensitive mutant. Map-based cloning showed that gsor300084 is a novel allelic mutant of the D61/OsBRI1 gene. The 444th amino acid, tryptophan (W), located in the LRR domain, is substituted by arginine
(R) and the mutation site is highly conserved among BRI1 orthologs from different plant species. These results suggest that this mutation site is important for BRI1 protein function and BRI1-mediated plant growth and development. More than ten allelic mutants of D61 have been reported in rice [4], [20], [32] and [33]. Only four (d61-2, d61-3, d61-5, and d61-7) have distinctive mutations in the selleck inhibitor LRR domain and show various degrees of phenotypic severity. In d61-2 the 491st amino acid, valine, is substituted by methionine, producing an intermediate phenotype [32]. d61-3 and d61-5 are two severe mutants that harbor the H420P and N426Y substitution, respectively. The phenotype of d61-7, in which
the 467th amino acid is changed from alanine to valine, is milder [33]. The gsor300084 mutant described in this study, harboring the W444R substitution, most resembles d61-2, showing an intermediate phenotype. Interestingly, the five mutation sites (H420P, N426Y, W444R, A467V, and V491M) are clustered together in a small portion of the LRR domain, which may be a potential essential motif for BRI1 function. Methane monooxygenase However, the manner in which these mutations affect the OsBRI1 function remains unclear. Our protein localization analysis revealed that defects other than subcellular localization account for the OsBRI1 dysfunction. The extracellular domain of Arabidopsis BRI1 contains 25 LRR repeats and a 70-amino acid island domain between the 21st and 22nd LRR [18]. The crystal structure of the extracellular domain of AtBRI1 has been resolved. The AtBRI1 LRR comprises a helical solenoid structure, while the separate island domain anchors onto the inner surface of the solenoid and spans six LRRs (LRR 17–22) [22] and [23]. The brassinolide molecule binds to a hydrophobic groove between the island domain and the inner surface of the LRRs. Thus both the island domain and the adjacent C-terminal LRR repeat (LRR 17–22) contribute to the formation of the hormone binding site [22] and [23].