Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Aichi 464-8601, Japan Bioscience and Biotechnology Center, Nagoya University, Nagoya, Aichi 464-8601, Japan.
Plant J. 2011 Aug;67(3):472-84. doi: 10.1111/j.1365-313X.2011.04610.x. Epub 2011 May 31.
Cytokinin is known to have negative effects on de novo auxin-induced root formation. However, the regulatory mechanisms of root initiation by both cytokinin and auxin are poorly understood. In this study, we characterized a rice mutant, termed crown rootless5 (crl5), which produced fewer crown roots and displayed impaired initiation of crown root primordia. The expression of CRL5, which encodes a member of the large AP2/ERF transcription factor family protein, was observed in the stem region where crown root initiation occurs. Exogenous auxin treatment induced CRL5 expression without de novo protein biosynthesis, which also required the degradation of AUX/IAA proteins. A putative auxin response element in the CRL5 promoter region specifically interacted with a rice ARF, demonstrating that CRL5 may be a direct target of an ARF, similar to CRL1/ADVENTITIOUS ROOTLESS1 (ARL1) that also regulates crown root initiation. A crl1 crl5 double mutant displayed an additive phenotype, indicating that these two genes function in different genetic pathways for crown root initiation. In addition, ProACT:CRL5/WT showed a cytokinin-resistant phenotype for crown root initiation, and also up-regulated the expression of two negative regulators of cytokinin signaling, OsRR1 and OsRR2, which were downregulated in crl5. Transgenic plants that over-expressed OsRR1 under the control of the CRL5 promoter in a crl5 mutant background produced a higher number of crown roots than the crl5 plant. Taken together, these results indicate that auxin-induced CRL5 promotes crown root initiation through repression of cytokinin signaling by positively regulating type-A RR, OsRR1.
细胞分裂素已知对新合成的生长素诱导的根形成有负面影响。然而，细胞分裂素和生长素启动根的调控机制还知之甚少。在这项研究中，我们对一个水稻突变体进行了研究，该突变体被命名为冠根缺失 5 号（crl5），它产生的冠根较少，并且冠根原基的起始受到损害。CRL5 编码一个大的 AP2/ERF 转录因子家族蛋白，其在发生冠根起始的茎区域表达。外源性生长素处理诱导 CRL5 表达，而无需新的蛋白质生物合成，这也需要 AUX/IAA 蛋白的降解。CRL5 启动子区域中的一个假定生长素反应元件与一个水稻 ARF 特异性相互作用，表明 CRL5 可能是 ARF 的直接靶标，类似于也调节冠根起始的 CRL1/ADVENTITIOUS ROOTLESS1（ARL1）。crl1 crl5 双突变体表现出累加表型，表明这两个基因在不同的遗传途径中发挥作用，以启动冠根的起始。此外，ProACT:CRL5/WT 对冠根起始表现出细胞分裂素抗性表型，并且还上调了两个细胞分裂素信号转导负调节剂 OsRR1 和 OsRR2 的表达，这两个基因在 crl5 中下调。在 crl5 突变体背景下，受 CRL5 启动子控制的 OsRR1 过表达的转基因植物产生的冠根数量多于 crl5 植物。总之，这些结果表明，生长素诱导的 CRL5 通过正向调节细胞分裂素信号转导的负调节剂 OsRR1，促进冠根的起始。
