Yang Guangxiao, Nakamura Hidemitsu, Ichikawa Hiroaki, Kitano Hidemi, Komatsu Setsuko
National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba 305-8602, Japan.
Phytochemistry. 2006 Jul;67(14):1442-54. doi: 10.1016/j.phytochem.2006.05.026. Epub 2006 Jun 30.
Brassinosteroids (BRs) are a group of plant hormones involved in a wide range of plant growth and developmental processes. To investigate the mechanism of BR action in monocots, a brassinolide (BL) upregulated gene designated OsBLE3 was identified, cloned and characterized in rice. It was mainly expressed in roots and leaf sheaths with levels of expression directly dependent on the dose of BL. In situ hybridization detected OsBLE3 mRNA in the shoot apical meristem, organ primordia and vascular tissue. Furthermore, its expression was enhanced by co-treatment with BL and low concentrations of IAA. These results, and the existence of auxin response elements in the 5'-flanking region of the OsBLE3 gene, indicate that OsBLE3 expression is under control of both BR and auxin. The GUS reporter gene driven by a 2277 bp OsBLE3 putative promoter was mainly expressed in vascular tissues, branch root primordia and was responsive to exogenous BL treatment. OsBLE3 transcript levels were greatly reduced in brd1 plants, a BL deficient mutant, compared to the wild type control. In OsBRI1 antisense transgenic rice and OsBLE3, the BR-insensitive mutant expression of OsBLE3 in response to exogenous BL treatment was significantly lower compared to that in control plants transformed with a vacant vector. Reduced OsBLE3 expression and growth retardation was also observed in OsBLE3 antisense transgenic rice plants. Internode cell length of the OsBLE3 antisense transgenic lines was about 70% of that in the vacant vector transformed control lines. These results suggest that OsBLE3 is involved in cell elongation in rice through dual regulation by BL and IAA.
油菜素甾醇（BRs）是一类参与多种植物生长和发育过程的植物激素。为了研究BR在单子叶植物中的作用机制，在水稻中鉴定、克隆并表征了一个油菜素内酯（BL）上调基因，命名为OsBLE3。它主要在根和叶鞘中表达，表达水平直接取决于BL的剂量。原位杂交在茎尖分生组织、器官原基和维管组织中检测到OsBLE3 mRNA。此外，与BL和低浓度IAA共同处理可增强其表达。这些结果以及OsBLE3基因5'侧翼区域中生长素反应元件的存在，表明OsBLE3的表达受BR和生长素的共同调控。由2277 bp OsBLE3推定启动子驱动的GUS报告基因主要在维管组织、侧根原基中表达，并对外源BL处理有反应。与野生型对照相比，BL缺陷突变体brd1植物中OsBLE3转录水平大大降低。在OsBRI1反义转基因水稻和OsBLE3中，与用空载体转化的对照植物相比，OsBLE3对外源BL处理的BR不敏感突变体表达显著降低。在OsBLE3反义转基因水稻植株中也观察到OsBLE3表达降低和生长迟缓。OsBLE3反义转基因系的节间细胞长度约为空载体转化对照系的70%。这些结果表明，OsBLE3通过BL和IAA的双重调控参与水稻细胞伸长。
