泛素受体类因子SUP1调控水稻耐盐性的分子基础

Soil salinization is one of the important factors affecting rice high yield. Increasing evidence shows that E3 ligases in ubiquitin-proteasome system (UPS) modulate plant growth, development and abiotic stress response in rice. Ubiquitin receptors, UBL/UBA proteins, play a role in protein degradation through ubiquitin-proteasome pathway in yeast and human, however, the regulatory function of UBL/UBA proteins in rice is unclear. To investigate the modulation of UBL/UBA proteins in rice salt stress response, 8 salt-induced genes encoding UBL/UBA proteins were identified from rice genome on the basis of bioinformatics and gene expression analyses, one of which is named SUP1 (Salt related UBL/UBA Protein 1). Our investigations showed that SUP1 could bind to poly-ubiquitin and RPT4, a subunit of 19S lid in UPS, indicating that SUP1 is a typical UBL/UBA protein that might be involved in the regulation of protein degradation. Moreover, SUP1 overexpression transgenic lines increased salt tolerance and RNAi transgenic lines showed more sensitivity to salt than wild type, evidencing that SUP1 might be involved in the regulation of rice salt stress response. Based on the above results, we further propose the project that plans to dissect the basic characteristics of SUP1 and the expression patterns of SUP1, and to analyze the molecular basis of SUP1 modulation in salt tolerance with SUP1 knock-out mutants, overexpression and RNAi transgenic lines.

泛素-蛋白酶体系统(UPS)在水稻生长发育和胁迫应答中均具有重要的调控功能，且泛素受体类因子UBL/UBA蛋白是UPS中重要的调控因子，但其在水稻生长发育及逆境胁迫应答中的功能不清楚。通过生物信息学和基因表达分析，我们从水稻基因组中鉴定出8个盐胁迫诱导表达的UBL/UBA基因，其中SUP1 (Salt related UBL/UBA Protein 1)可与多聚泛素结合，并能够与蛋白酶体19S盖子中的RPT4相互作用，表明SUP1具有典型的UBL/UBA蛋白特性。此外，超表达SUP1转基因株系增加了水稻耐盐性，而SUP1表达降低的转基因株系耐盐性降低，表明SUP1参与水稻耐盐性的调控。本项目拟在以上研究基础上，剖析SUP1的基本特性及表达模式；利用SUP1突变体、超表达和RNAi转基因水稻材料剖析SUP1在水稻耐盐性中的分子途径，以期阐明SUP1在水稻耐盐性中的分子基础。

本项目的研究目标是阐明水稻泛素受体类因子UBL/UBA蛋白SUP1（后改名为OsDSK2b）通过调控赤霉素代谢参与盐胁迫应答的分子基础。通过4年的实施，我们圆满地完成了预期的研究内容。泛素-蛋白酶体系统（UPS）是调节植物生长发育和逆境胁迫应答的重要途径，UBL/UBA蛋白作为UPS的重要组份，其在水稻中的调节功能尚不清楚。本研究发现水稻中OsDSK2b还有一个同源蛋白，命名为OsDSK2a，且两个同源蛋白均可负调控水稻耐盐性，但只有OsDSK2a功能缺失突变体表现出生长发育延缓，因此OsDSK2a与OsDSK2b在功能上有所差异。但在鉴定与26S蛋白酶体的互作时，只发现OsDSK2b与蛋白酶体亚基RPT4互作，且OsDSK2a可以与OsDSK2b互作，说明它们可能通过形成二聚体来发挥功能。进一步研究发现OsDSK2a通过促进水稻赤霉素代谢负调控因子EUI的降解来参与赤霉素代谢调控，同时盐胁迫可以促进OsDSK2a蛋白丰度降低，从而导致盐胁迫条件下EUI蛋白积累增加来抑制生长。本研究解析了水稻在盐胁迫下生长受到抑制的分子机理，证明了赤霉素负调控水稻耐盐性，可以为提高植物耐逆性提供理论基础。