Komorisono Masahiko, Ueguchi-Tanaka Miyako, Aichi Ikuko, Hasegawa Yasuko, Ashikari Motoyuki, Kitano Hidemi, Matsuoka Makoto, Sazuka Takashi
Bioscience and Biotechnology Center, Nagoya University, Nagoya, Aichi 464-8601, Japan.
Plant Physiol. 2005 Aug;138(4):1982-93. doi: 10.1104/pp.105.062968. Epub 2005 Jul 22.
Molecular genetic studies of plant dwarf mutants have indicated that gibberellin (GA) and brassinosteroid (BR) are two major factors that determine plant height; dwarf mutants that are caused by other defects are relatively rare, especially in monocot species. Here, we report a rice (Oryza sativa) dwarf mutant, dwarf and gladius leaf 1 (dgl1), which exhibits only minimal response to GA and BR. In addition to the dwarf phenotype, dgl1 produces leaves with abnormally rounded tip regions. Positional cloning of DGL1 revealed that it encodes a 60-kD microtubule-severing katanin-like protein. The protein was found to be important in cell elongation and division, based on the observed cell phenotypes. GA biosynthetic genes are up-regulated in dgl1, but the expression of BR biosynthetic genes is not enhanced. The enhanced expression of GA biosynthetic genes in dgl1 is not caused by inappropriate GA signaling because the expression of these genes was repressed by GA3 treatment, and degradation of the rice DELLA protein SLR1 was triggered by GA3 in this mutant. Instead, aberrant microtubule organization caused by the loss of the microtubule-severing function of DGL1 may result in enhanced expression of GA biosynthetic genes in that enhanced expression was also observed in a BR-deficient mutant with aberrant microtubule organization. These results suggest that the function of DGL1 is important for cell and organ elongation in rice, and aberrant DGL1-mediated microtubule organization causes up-regulation of gibberellin biosynthetic genes independently of gibberellin signaling.
植物矮化突变体的分子遗传学研究表明，赤霉素（GA）和油菜素内酯（BR）是决定株高的两个主要因素；由其他缺陷引起的矮化突变体相对较少，尤其是在单子叶植物中。在此，我们报道了一个水稻（Oryza sativa）矮化突变体——矮化剑叶1（dgl1），它对GA和BR仅表现出最小反应。除了矮化表型外，dgl1还产生叶尖区域异常圆润的叶片。DGL1的图位克隆显示，它编码一种60-kD的类似katanin的微管切断蛋白。基于观察到的细胞表型，发现该蛋白在细胞伸长和分裂中很重要。GA生物合成基因在dgl1中上调，但BR生物合成基因的表达未增强。dgl1中GA生物合成基因的增强表达不是由不适当的GA信号传导引起的，因为这些基因的表达在GA3处理下受到抑制，并且在该突变体中GA3触发了水稻DELLA蛋白SLR1的降解。相反，由于DGL1的微管切断功能丧失导致的异常微管组织可能导致GA生物合成基因的表达增强，因为在具有异常微管组织的BR缺陷突变体中也观察到了这种增强表达。这些结果表明，DGL1的功能对水稻中的细胞和器官伸长很重要，并且异常的DGL1介导的微管组织导致赤霉素生物合成基因上调，而与赤霉素信号传导无关。
