番茄低温弱光逆境应答中油菜素内酯的抗逆调控机制

Chilling at low light is a major stress for most temperate horticultural crops. We have found that reactive oxygen species (ROS) produced by NADPH oxidase are mediators of stress tolerance in cucumber or tomato response to chilling stress and brassinosteroids (BRs). Based on current progress, we will use a series of tomato mutants, wild accessions with different chilling sensitivity, transgenic lines and RNAi plants of specific genes to study the homeostasis of BRs and ROS in response to environment changes, with emphasis on chilling at low light, a stress frequently encountered by tomato during winter-spring transition. We will study the role of CBF regulation by BRs, light and redox signal in chilling stress tolerance and dissect the role of ROS as second messengers in BR-induced stress response. Through transcriptomic analysis and forward and reverse genetic studies, we will identify genes potentially involved in BR-induced chilling stress tolerance and study the functions of the genes, and finally dissect the signaling pathway, critical components and mechanisms of BR and its second redox signals for their role in photosynthesis through activating the redox sensitive enzymes in photosynthetic apparatus and in the adaptation of chill stress. The study will deepen the understanding of the molecular mechanisms of interplay between BRs and ROS in the regulation of tolerance and adaptation to temperature stresses. The research of the project will found theoretic bases for establishing a novel technology to regulate the vegetable tolerance to low temperature at low light based on interplay of BRs, light and ROS, and therefore is of fundamental significance for horticultural science and industry.

低温弱光是喜温园艺作物生产中的主要逆境。项目在发现番茄等低温驯化和油菜素内酯BRs通过激发质膜活性氧ROS产生抗逆反应的基础上，以代表性园艺作物番茄中不同突变体、不同温敏性基因型和基因沉默或过表达植株为材料，以番茄生产中经常遭遇的低温弱光逆境为重点，研究其响应中BRs信号和ROS产生变化；明确BRs、光和氧化还原redox信号同低温抗性及其同CBF的关系，探明ROS作为第二信使在BRs诱导抗逆反应信号途径中的作用；利用转录组分析、正向和反向遗传学思路，鉴定相关基因功能，明确BRs及其次生redox信号如何通过活化光合作用中redox敏感蛋白提高光合效率和温度适应性的信号转导途径、关键节点及其作用机理。研究可望加深BRs和ROS互作诱导作物对低温弱光抗性分子机制的理解，为建立一条基于BRs、光环境和ROS信号互作提高蔬菜低温弱光抗性和光合效率的新途径奠定理论基础，具有重要的科学与现实意义。

冬春低温寡照导致蔬菜产量低位徘徊，是制约设施蔬菜高产稳产和冬春蔬菜供应的瓶颈。本项目针对低温寡照下设施蔬菜冷害常发但调控措施匮乏的现状，围绕BR和光信号调控抗冷性的机制展开研究，取得了一系列成果。.1、.发现蔬菜中油菜素内酯（BR）是调控番茄抗冷性的关键信号，并揭示其作用机制。获得了不同BR合成能力的番茄植株，明确了内源BR对生长和抗冷性的影响。揭示了低温下BR含量上升，BZR1蛋白明显积累，同时去磷酸化BZR1比例显著提高。比较bzr1缺失突变体和BZR1-OE植株的低温表型，明确BR下游转录因子BZR1对于调控低温抗性具有重要作用。利用ChIP和酵母单杂交证实BZR1通过直接结合CBFs调控其基因表达进而提高抗冷性。.2、.发现质外体H2O2与BR互作调控番茄抗冷性的机制。发现BR通过BZR1直接调控NADPH氧化酶编码基因RBOH1，并促进质外体H2O2积累。ROS诱导环式电子流(CEF)，提高光保护相关蛋白水平，并通过诱导谷氧还蛋白GRXS12和S14提高番茄抗冷性。RBOH1-RNAi干涉抑制BR对上述保护机制的调控，导致抗冷性显著下降。RBOH1可以进一步通过调控redox平衡参与调控BRs信号及BZR1介导的抗冷基因CBFs转录调控。.3、.发现HY5介导的远红光信号与BR信号协同诱导番茄低温抗性的机制。明确了低温下远红光及其受体PHYA激活转录因子HY5，调控抗逆激素ABA和JA的合成与信号，提高番茄低温抗性，但红光及其受体PHYB介导的光信号途径对低温抗性有抑制作用。进一步发现远红光信号途径或PHYB缺失诱导BR合成基因表达上调、BZR1蛋白积累以及去磷酸化BZR1比例上升，表明HY5介导的远红光信号和BR信号在调控低温抗性中存在协同作用。