Leaf angle is a key factor in plant architecture and crop yield. Brassinosteroids (BRs) regulate many developmental processes, especially the leaf angle in monocots. However, the BR signalling pathway is complex and includes many unknown members. Here, we propose that Oryza sativa BRASSINOSTEROID-RESPONSIVE LEAF ANGLE REGULATOR 1 (OsBLR1) encodes a bHLH transcription factor, and positively regulates BR signalling to increase the leaf angle and grain length in rice (Oryza sativa L.). Lines overexpressing OsBLR1 (blr1-D and BLR1-OE-1/2/3) had similar traits, with increased leaf angle and grain length. Conversely, OsBLR1-knockout mutants (blr1-1/2/3) had erect leaves and shorter grains. Lamina joint inclination, coleoptile elongation, and root elongation assay results indicated that these overexpression lines were more sensitive to BR, while the knockout mutants were less sensitive. There was no significant difference in the endogenous BR contents of blr1-1/2 and wild-type plants. These results suggest that OsBLR1 is involved in BR signal transduction. The blr1-D mutant, with increased cell growth in the lamina joint and smaller leaf midrib, showed significant changes in gene expression related to the cell wall and leaf development compared with wild-type plants; furthermore, the cellulose and protopectin contents in blr1-D were reduced, which resulted in the increased leaf angle and bent leaves. As the potential downstream target gene of OsBLR1, the REGULATOR OF LEAF INCLINATION1 (OsRLI1) gene expression was up-regulated in OsBLR1-overexpression lines and down-regulated in OsBLR1-knockout mutants. Moreover, we screened OsRACK1A as an interaction protein of OsBLR1 using a yeast two-hybrid assay and glutathione-S-transferase pull-down.

中文翻译：

---

基本的螺旋-环-螺旋转录因子OsBLR1通过油菜素类固醇信号传导调节水稻的叶角。

叶角是植物结构和农作物产量的关键因素。油菜素类固醇（BRs）调节许多发育过程，尤其是单子叶植物的叶片角。然而，BR信号传导途径是复杂的并且包括许多未知成员。在这里，我们提出水稻（Oryza sativa）的油菜籽甾醇响应性叶片角调节剂1（OsBLR1）编码bHLH转录因子，并正向调节BR信号传导，从而增加水稻（Oryza sativa L.）的叶片角和籽粒长度。过表达OsBLR1的品系（blr1-D和BLR1-OE-1 / 2/3）具有相似的性状，但叶片角和籽粒长度增加。相反，OsBLR1基因敲除突变体（blr1-1 / 2/3）具有直立的叶片和较短的籽粒。椎板的关节倾斜度，胚芽鞘伸长率和根伸长率测定结果表明，这些过表达谱系对BR更敏感，而敲除突变体的敏感性较低。blr1-1 / 2和野生型植物的内源BR含量没有显着差异。这些结果表明OsBLR1参与BR信号转导。与野生型植物相比，blr1-D突变体的椎板关节中的细胞生长增加并且叶片中脉变小，与细胞壁和叶片发育相关的基因表达发生了显着变化。此外，blr1-D中纤维素和原果胶的含量降低，导致叶片角度增加和叶片弯曲。作为OsBLR1的潜在下游靶基因，“叶向倾斜基因1”（OsRLI1）基因的表达在OsBLR1过表达系中上调，而在OsBLR1基因敲除突变体中下调。此外，