泛素连接酶LPS1调控植物磷转运的机制研究

Phosphorus is a major essential nutrient for plant growth and development, and serves various basic biological functions in plant life cycle. Phosphate (Pi) is transported into roots, and translocated from roots to shoots through xylem. Arabidopsis PHO1 plays an important role in Pi translocation from roots to shoots, and the expression of PHO1 is obviously induced by low-Pi stress. Our previous report demonstrates that transcription factor WRKY6 down-regulates Pi translocation by directly repressing PHO1 expression under Pi-sufficient condition. During Pi starvation, the WRKY6 is degraded via 26S proteosome mediated proteolysis. Recently, we find an E3 ligase mutant, named lps1, shows low-Pi sensitive phenotypes and low shoot Pi content, similar to the WRKY6-overexpressing line and pho1 mutant, indicating that LPS1 is involved in Arabidopsis Pi translocation. The LPS1 is interacted with WRKY6 in the nucleus, and during Pi starvation, the WRKY6 degradation in the lps1 mutant is much slower that that in wild-type plants, indicating that LPS1 modulates WRKY6 degradation. In this project, we will reveal the molecular mechanism of LPS1 modulating Pi translocation.

磷是植物必需大量元素之一，参与植物的细胞构成、物质代谢和能量代谢等。磷进入植物根部后经木质部运输到冠部。PHO1蛋白负责拟南芥的根冠磷转运，且PHO1基因受低磷胁迫诱导表达。我们前期研究结果发现，转录因子WRKY6负调控PHO1表达，进而负调控根冠磷转运；低磷胁迫时，WRKY6蛋白被降解，该降解依赖于26S蛋白酶体途径，暗示E3泛素连接酶参与调控根冠磷转运。通过突变体表型筛选，我们发现一个泛素连接酶突变体，命名为lps1，表现低磷敏感表型和低的冠部磷含量，与WRKY6过量表达株系、pho1突变体类似，说明LPS1可能参与调控根冠磷转运。LPS1与WRKY6在细胞核互作，并且低磷胁迫时，lps1突变体的WRKY6蛋白降解明显减弱，暗示LPS1可能调控WRKY6的蛋白降解。本申请项目将探究泛素连接酶LPS1调控根冠磷转运的分子机制以及LPS1如何感知低磷信号。

磷是植物必需大量元素之一，参与植物的细胞构成、物质代谢和能量代谢。磷素主要以无机磷形式被植物根系吸收，通过木质部运输到地上部。拟南芥PHO1在木质部表达，负责磷从根部向冠部的转运。我们前期的研究结果发现，磷充足时，转录因子WRKY6直接负调控PHO1的表达，抑制磷素从根部向冠部转运；低磷胁迫时，WRKY6蛋白被降解，PHO1的抑制被解除，PHO1表达上调，有利于磷素从根部向冠部转运（Chen et al., 2009, Plant Cell, 167:1579-1591）。为了探究低磷胁迫条件下WRKY6蛋白的降解分子机制，我们筛选了可能的E3泛素连接酶的突变体的低磷表型，发现一个泛素连接酶PRU1/LPS1的突变体pru1表现低磷敏感表型和磷素根冠转运缺陷，PRU1能恢复突变体pru1的磷根冠转运缺陷，说明PRU1参与植物磷素的根冠转运。进一步的植物生理、分子生化和遗传学实验结果显示，低磷胁迫条件下，PRU1与WRKY6蛋白互作，泛素化修饰WRKY6蛋白，被泛素化修饰的WRKY6蛋白经26S蛋白酶体途径降解；WRKY6蛋白降解后， PHO1的转录抑制被解除，PHO1表达上调，有利于无机磷从根部向冠部转运。调控通路PRU1-WRKY6-PHO1的解析有利于人们更好地了解植物体内磷素分配的分子机制，为通过基因工程方法提高作物磷素利用效率提供了思路和候选基因。