Shanghai Key Laboratory of Plant Molecular Sciences, College of Life Sciences, Shanghai Normal University, Shanghai, China.
State Key Laboratory of Genetic Engineering, Institute of Genetics, Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai, China.
Plant Biotechnol J. 2020 Feb;18(2):429-442. doi: 10.1111/pbi.13209. Epub 2019 Aug 7.
The rice root system is important for growth. The crosstalk between auxin and cytokinin mediates root initiation and elongation. However, it remains unclear how the transcriptional network upstream of the auxin and cytokinin signalling pathways determines root development. Here, we observed that the knockdown of OsNAC2, which encodes a NAC transcription factor, increased the primary root length and the number of crown roots. OsNAC2 predominantly expressed in primary root tips, crown roots and lateral root primordia, implying it influences root development. Molecular analyses revealed that the expressions of auxin- and cytokinin-responsive genes were affected in OsNAC2-overexpressing (OsNAC2-OX; ON7 and ON11), RNA interference (OsNAC2-RNAi; RNAi25 and RNAi31) and CRISPR/Cas9 plants. Additionally, OsNAC2 can directly bind to the promoters of IAA inactivation-related genes (GH3.6 and GH3.8), an IAA signalling-related gene (OsARF25), and a cytokinin oxidase gene (OsCKX4). Furthermore, genetic analysis of ON11/osgh3.6 and RNAi31/osckx4 homozygote confirmed that OsCKX4 and OsGH3.6 functioned downstream of OsNAC2. The mRNA levels of CROWN ROOTLESS (CRL) genes and cyclin-dependent protein kinase (CDK) genes increased in OsNAC2-RNAi and OsNAC2-cas9 lines while reduced in OsNAC2-OX lines. Thus, we describe that OsNAC2 functions as an upstream integrator of auxin and cytokinin signals that affect CRL and CDK production to regulate cell division during root development. This novel auxin-OsNAC2-cytokinin model should provide a new insight into the understanding of NAC TFs and crosstalk of auxin and cytokinin pathway, and can be potentially applied in agriculture to enhance rice yields by genetic approaches.
水稻根系对于生长很重要。生长素和细胞分裂素的串扰调节根的起始和伸长。然而,生长素和细胞分裂素信号通路上游的转录网络如何决定根发育仍不清楚。在这里,我们观察到,编码 NAC 转录因子的 OsNAC2 的敲低增加了主根长度和冠根数量。OsNAC2 主要在主根根尖、冠根和侧根原基中表达,表明它影响根发育。分子分析表明,在 OsNAC2 过表达(OsNAC2-OX;ON7 和 ON11)、RNA 干扰(OsNAC2-RNAi;RNAi25 和 RNAi31)和 CRISPR/Cas9 植物中,生长素和细胞分裂素反应基因的表达受到影响。此外,OsNAC2 可以直接结合生长素失活相关基因(GH3.6 和 GH3.8)、生长素信号相关基因(OsARF25)和细胞分裂素氧化酶基因(OsCKX4)的启动子。此外,ON11/osgh3.6 和 RNAi31/osckx4 纯合子的遗传分析证实,OsCKX4 和 OsGH3.6 是 OsNAC2 的下游基因。在 OsNAC2-RNAi 和 OsNAC2-cas9 系中,CRL 基因和细胞周期蛋白依赖性蛋白激酶(CDK)基因的 mRNA 水平增加,而在 OsNAC2-OX 系中降低。因此,我们描述了 OsNAC2 作为生长素和细胞分裂素信号的上游整合因子,通过调节细胞分裂来影响 CRL 和 CDK 的产生,从而调节根发育过程中的细胞分裂。这个新的生长素-OsNAC2-细胞分裂素模型应该为理解 NAC TF 和生长素和细胞分裂素途径的串扰提供新的见解,并可以通过遗传方法在农业中应用于提高水稻产量。