New Phytologist:农科院作物所李文学研究组解析泛素化调控植物适应
2016年12月29日，国际期刊《New Phytologist》杂志在线发表了中国农业科学院作物科学研究所玉米分子育种技术和应用创新团队李文学研究组题为“Nitrogen Limitation Adaptation (NLA) is involved in source-to-sink remobilization of nitrate by mediating the degradation of NRT1.7 in Arabidopsis”的研究论文，论文揭示了E3泛素化连接酶NLA直接降解氮转运蛋白NRT1.7，增强氮素从老叶向新叶的再分配，提高植物耐受低氮胁迫能力。作科所博士研究生刘文文为论文第一作者，李文学研究员为论文的通讯作者。
氮的再分配是植物提高氮利用效率的关键步骤之一。不同器官之间的氮转运主要由硝态氮转运蛋白(Nitrate Transporter, NRT)负责完成，但是目前对于NRT 蛋白的调控机制知之甚少。
研究人员通过氮素测定、稳定同位素吸收和涂抹示踪等实验证实，在低氮培养条件下，nla突变株老叶变黄是由于突变株体内氮素由老叶向新叶中的转运加快导致;BiFC、膜蛋白酵母双杂、Pull-down、Co-IP、western blot等生化与分子实验证实了泛素化连接酶NLA对硝酸盐转运蛋白NRT1.7进行泛素化降解;NLA为miR827的靶基因，mir827敲除突变株及MIR827过表达植株中NLA及NRT1.7转录本及蛋白丰度检测表明缺氮在翻译水平对NLA的负调控依赖于miR827的表达。该研究为深入了解泛素化及miRNA在氮营养限制条件下的功能和作用方式提供了实验依据, 也为培育高效且抗逆的作物品种奠定了分子生物学基础。
NRT1.7是NLA的泛素化底物示意图
原文链接:
Nitrogen Limitation Adaptation (NLA) is involved in source-to-sink remobilization of nitrate by mediating the degradation of NRT1.7 in Arabidopsis
原文摘要：
Recent studies on nitrate transporters (NRTs) have greatly increased our knowledge of the mechanisms regulating nitrogen (N) homeostasis in plants. However, an understanding of how these NRTs are regulated is still lacking.
The nitrogen limitation adaptation (nla) mutant is hypersensitive to N limitation. In the nla mutant, 15N-nitrate spotted on old leaves preferentially accumulated in the youngest leaves. Analysis of leaf cross-sections indicated that NLA expression was expressed in the sieve element and companion cell system. The results of bimolecular fluorescence complementation (BiFC), split-ubiquitin yeast two-hybrid and co-immunoprecipitation (CoIP) assays demonstrated that NLA interacts with NRT1.7 in the plasma membrane.
The following findings suggest that NLA directs the ubiquitination of NRT1.7: the down-regulation of NRT1.7 protein abundance in35S::NLA/35S::Myc-NRT1.7 double transgenic plants compared with35S::Myc-NRT1.7 transgenic plants; the up-regulation of NRT1.7 protein abundance in the nla mutant compared with wild-type plants; and the direct degradation of truncated NRT1.7 recombinant protein by NLA. Furthermore, analysis of NLA and NRT1.7 protein abundance in mirna827knock-out plants showed that N deficiency-guided translational repression of NLA depends on miRNA827.
Our findings reveal that plants regulate source-to-sink remobilization of nitrate by the ubiquitin-mediated post-translational regulatory pathway.
作者：李文学
