LAZY1通过BR途径调控水稻叶夹角的发育

叶夹角的大小直接影响水稻叶面积指数，进而调控群体光合作用，是水稻株型育种中重要的指标，研究其发育机制对水稻株型育种具有重要的意义。利用EMS诱变籼型水稻保持系西大1B，获得一个植株散生且叶夹角变大的突变体s524。田间种植条件下，苗期s524的叶夹角极显著大于野生型；分蘖期s524的分蘖角极显著增大，株型松散；成熟期s524整个植株呈匍匐状生长。而野生型株型在整个生育期均保持相对紧凑，叶夹角较小。石蜡切片分析显示，s524叶夹角增大是由叶枕近轴面细胞变大造成的。s524的主要农艺性状与野生型相比无明显变化。遗传分析表明该性状受1对隐性核基因控制，利用SSR标记进行基因定位，最终将S524定位在第11染色体标记RM4746和RM26742之间324 kb的物理范围内，包含散生基因LAZY1。测序结果显示s524突变体在LAZY1第3外显子上发生了一个T到C的碱基替换，导致第143位氨基酸由野生型的缬氨酸突变为丙氨酸，表明s524是一个新的LAZY1等位突变体。s524对外源油菜素内酯(BR)的敏感性降低，BR信号传导途径关键基因BU1在s524中的表达上调了近10倍，早期研究表明BU1基因的过表达可导致叶夹角变大。推测LAZY1/S524可能通过BR信号传导途径调控水稻叶夹角的发育。

LAZY1 Regulates the Development of Rice Leaf Angle through BR Pathway

The angle of rice leaf, as an important agronomic trait, influences leaf area index and yield in rice. Leaf angle mutant identification is of significant importance in rice breeding based on ideal plant architecture. A mutant s524, derived from the progeny of EMS-treated indica rice Xida1B, showed significantly larger leaf angle than the wild type. At tillering stage, the tiller angle and leaf angle of s524 increased and the whole plant crept, while the wild type in whole growth period maintained relatively compact phenotype. Longitudinal sections of the epidermis of pulvinus showed that the enlarged leaf angle of the mutant was mainly due to the much-elongated adaxial cells. The main agronomic traits of s524 did not change significantly compared with those of the wild-type. Genetic analysis suggested that the mutational traits were controlled by a recessive nuclear gene, which was finely mapped between SSR markers RM4746 and RM26742 on chromosome 11 with a physical distance of 324 kb. LAZY1 in the restricted region regulates rice tiller angle development. Sequencing revealed that a base substitution from T to C occurred on the third exon of LAZY1, leading to the amino acid change from valine to alanine at 143th protein sequence. Hormone treatment test indicated that BR sensitivity was reduced in s524. Quantitative analysis demonstrated that the expression of BR signaling related gene BU1 was obviously up-regulated. The previous study showed that over-expression of BU1 could enlarge rice leaf angle. Our research suggests that LAZY1/S524 may regulate the development of leaf angle through BR conduction pathway.