Inukai Yoshiaki, Sakamoto Tomoaki, Ueguchi-Tanaka Miyako, Shibata Yohko, Gomi Kenji, Umemura Iichiro, Hasegawa Yasuko, Ashikari Motoyuki, Kitano Hidemi, Matsuoka Makoto
Bioscience and Biotechnology Center, Nagoya University, Nagoya, Aichi 464-8601, Japan.
Plant Cell. 2005 May;17(5):1387-96. doi: 10.1105/tpc.105.030981. Epub 2005 Apr 13.
Although the importance of auxin in root development is well known, the molecular mechanisms involved are still unknown. We characterized a rice (Oryza sativa) mutant defective in crown root formation, crown rootless1 (crl1). The crl1 mutant showed additional auxin-related abnormal phenotypic traits in the roots, such as decreased lateral root number, auxin insensitivity in lateral root formation, and impaired root gravitropism, whereas no abnormal phenotypic traits were observed in aboveground organs. Expression of Crl1, which encodes a member of the plant-specific ASYMMETRIC LEAVES2/LATERAL ORGAN BOUNDARIES protein family, was localized in tissues where crown and lateral roots are initiated and overlapped with beta-glucuronidase staining controlled by the DR5 promoter. Exogenous auxin treatment induced Crl1 expression without de novo protein biosynthesis, and this induction required the degradation of AUXIN/INDOLE-3-ACETIC ACID proteins. Crl1 contains two putative auxin response elements (AuxREs) in its promoter region. The proximal AuxRE specifically interacted with a rice AUXIN RESPONSE FACTOR (ARF) and acted as a cis-motif for Crl1 expression. We conclude that Crl1 encodes a positive regulator for crown and lateral root formation and that its expression is directly regulated by an ARF in the auxin signaling pathway.
尽管生长素在根系发育中的重要性已广为人知，但其涉及的分子机制仍不清楚。我们鉴定了一个在冠根形成方面存在缺陷的水稻（Oryza sativa）突变体，即无冠根1（crl1）。crl1突变体在根中还表现出其他与生长素相关的异常表型特征，如侧根数量减少、侧根形成过程中对生长素不敏感以及根向重力性受损，而地上器官未观察到异常表型特征。Crl1编码植物特有的AS1/LOB蛋白家族的一个成员，其表达定位于冠根和侧根起始的组织中，并与由DR5启动子控制的β-葡萄糖醛酸酶染色重叠。外源生长素处理可诱导Crl1表达而无需从头合成蛋白质，且这种诱导需要生长素/吲哚-3-乙酸蛋白的降解。Crl1在其启动子区域包含两个假定的生长素反应元件（AuxREs）。近端AuxRE与水稻生长素反应因子（ARF）特异性相互作用，并作为Crl1表达的顺式基序。我们得出结论，Crl1编码冠根和侧根形成的正调控因子，且其表达受生长素信号通路中的ARF直接调控。
