南京农大揭示了稻瘟病菌监控水稻免疫反应机制
近日，PLoS Pathogens在线发表了南京农大张正光教授团队题为“MoYvh1 Subverts Rice Defense through Functions of Ribosomal Protein MoMrt4 inMagnaporthe oryzae”的研究论文，揭示了稻瘟病菌监控水稻免疫反应机制。
- Published: April 23, 2018
- https://doi.org/10.1371/journal.ppat.1007016
稻瘟病菌引起的水稻稻瘟病是粮食作物上最大的毁灭性病害，威胁着全球粮食安全，每年给我国造成30亿公斤以上的粮食损失。该病菌侵染水稻时，可激发水稻的免疫反应，但是病菌如何监控水稻的免疫反应仍不清楚。
病菌与水稻的互作堪比充斥硝烟的战场，稻瘟病菌在侵染水稻早期时，水稻会产生大量活性氧激发免疫反应，构筑起一道“马奇诺防线”，抑制病原菌的侵染，而病菌可分泌大量效应蛋白到水稻中向其免疫系统发起攻击。但是作为半活体营养的致病真菌，为了防止寄主细胞直接死亡，病菌也不能肆无忌惮的将效应蛋白作为武器“倾泻”在水稻中。因此病菌对于水稻免疫系统的监控在调控病菌致病力中具有至关重要的作用。该团队前期的研究中鉴定到蛋白磷酸酶MoYvh1控制病菌致病力（MPMI，2016）。
最新研究成果表明，当监测到水稻免疫系统给予的压力后，稻瘟病菌会利用两个热激蛋白MoSsb1、MoSsz1“挟持”MoYvh1进入细胞核，在细胞核内MoYvh1加速核糖体的成熟，促进病菌合成更多效应蛋白，为病菌干扰水稻的免疫反应输送充足的“弹药”，从而成功侵染水稻。该研究拓展了人们对植物病原真菌监控寄主免疫反应的认识，揭示了稻瘟病菌“诡计多端”的真面目，有助于认识病原菌的致病机理，同时可望为设计高效、低毒的稻瘟病控制策略提供参考。该项目得到了国家自然科学基金重点项目和国家杰出青年科学基金的资助。
植保学院在读博士生刘昕宇为论文第一作者，国家杰出青年科学基金获得者张正光教授为通讯作者。郑小波教授、张海峰教授、美国路易斯安娜州立大学的Ping Wang教授参与了该研究。
Abstract
The accumulation of the reactive oxygen species (ROS) in rice is important in its interaction with the rice blast fungus Magnaporthe oryzae during which the pathogen scavenges ROS through the production of extracellular enzymes that promote blast. We previously characterized the MoYvh1 protein phosphatase from M. oryzae that plays a role in scavenging of ROS. To understand the underlying mechanism, we found that MoYvh1 is translocated into the nucleus following oxidative stress and that this translocation is dependent on MoSsb1 and MoSsz1 that are homologous to heat-shock protein 70 (Hsp70) proteins. In addition, we established a link between MoYvh1 and MoMrt4, a ribosome maturation factor homolog whose function also involves shuttling between the cytoplasm and the nucleus. Moreover, we found that MoYvh1 regulates the production of extracellular proteins that modulate rice-immunity. Taking together, our evidence suggests that functions of MoYvh1 in regulating ROS scavenging require its nucleocytoplasmic shuttling and the partner proteins MoSsb1 and MoSsz1, as well as MoMrt4. Our findings provide novel insights into the mechanism by which M. oryzaeresponds to and subverts host immunity through the regulation of ribosome biogenesis and protein biosynthesis.
Author summary
ROS accumulation is important for the interaction between the blast fungus M. oryzae and its rice host. The protein phosphatase MoYvh1 affects the scavenging of host-derived ROS that promotes M. oryzae infection. We found that MoYvh1 is translocated to the nucleus under oxidative stress by a mechanism that is dependent on its interactions with MoSsb1 and MoSsz1. MoYvh1 triggers the release of MoMrt4 from the ribosome in the nucleus that contributes to ribosome maturation. Importantly, we have provided evidence to demonstrate that MoYvh1 is important for the synthesis of extracellular proteins that are involved in ROS scavenging. Our findings provide insight into the mechanism by which M. oryzae responds to host immunity through MoYvh1 that regulates ribosome function to evade the host defense response.