However, coleoptile and root length did not vary significantly after BR treatment ( Fig. 3-A, B and C). A more sensitive method, lamina joint inclination assay [30], was used to examine sensitivity of gsor300084 to BL. In the absence of BL, the bending angle of the leaf blade in gsor300084 was smaller than that in wild-type plants ( Fig. 4-A, B). In the presence of 1 μmol L− 1 BL, the leaf angle increased dramatically in the wild type but remained almost unchanged in the gsor300084 mutant ( Fig. 4-A, B). This result further confirmed that gsor300084 mutant seedlings were less sensitive to exogenous

BL than wild-type seedlings. Primary mapping using 20 F2 mutant individuals derived from a cross between gsor300084 and the indica variety Dular ICG-001 revealed that the mutation resided on the long arm of

chromosome 1 between the InDel markers R1–12 and R1–13 ( Fig. 5-A and Table 2). Fine Pifithrin-�� datasheet mapping using 7 new inDel markers and 358 F2 mutant individuals narrowed the location to a 107 kb region. According to the MSU Rice Genome Annotation Project (http://rice.plantbiology.msu.edu/), the D61 gene (LOC_Os01g52050) encoding the putative BR receptor OsBRI1 is located within this region. Accordingly, the genomic DNA fragment of the D61 gene from both gsor300084 and Matsumae was amplified and sequenced. Sequence analysis revealed that only the 1330th base in the D61 coding region was changed from T to A, causing the 444th amino PIK-5 acid tryptophan (W) to be substituted by arginine (R). This mutation was located in the LRR region of OsBRI1 and adjacent to the island domain ( Fig. 5-A). Sequence alignment among BRI1 orthologs from different plant species revealed that this mutation site is highly conserved ( Fig. 5-B), indicating that this residue is important for BRI1 protein function. Although leucine-rich repeats (LRRs) are frequently involved in protein–protein interactions, a previous

study had shown that mutations in the LRR domain led to changed protein subcellular localization [31]. We accordingly wondered whether the W444R substitution has any effects on the subcellular localization of OsBRI1. The wild-type and gsor300084 mutant allele of the D61 gene fused in-frame with the sGFP gene was transformed into rice protoplasts. Fig. 6 presents a confocal microscopy analysis of OsBRI1 expression, showing that OsBRI1::GFP fluorescence is localized to the cell surface. Thus the OsBRI1-directed GFP fluorescence is at the cell wall or plasma membrane but not in the cytoplasm. Since the cell wall has been removed during the preparation of protoplasts from rice seedlings, OsBRI1 should be localized at the plasma membrane. This result is consistent with the subcellular localization analysis of the Arabidopsis BRI1 protein, in which a plasmolysis experiment confirmed that BRI1 was localized at the plasma membrane rather than at the cell wall [24] and [26].