番茄Spr9基因调控系统素/茉莉酸介导的植物免疫反应的分子机理

In tomato, the peptide signal systemin and the oxylipin signal jasmonic acid (JA) play important roles in regulating plant defenses against wounding, insect attack and pathogen. A wealth of evidence indicates that systemin and JA work together in the same signaling pathway to activate the expression of Proteinase inhibitors (PIs) and other defense-related genes. Toward understanding the molecular mechanism of systemin/JA-mediated systemic defense signaling in tomato, we are conducting a genetic screen to identify spr mutants that suppress the constitutive wound signaling phenotype of the 35S::PS (Overexpression of the prosystemin) plants. spr9, one of the spr mutants, is defective in wound-induced JA accumulation and expression of defense-related genes. Application of exogenous JA can rescue the defect of wound-induced gene expression in spr9, indicates that Spr9 affects JA biosynthesis. In addition，spr9 plants exhibit severely compromised resistance to chewing insect and Botrytis cinerea whereas enhanced resistance to Pseudomonas syringae, and salicylic acid (SA)-induced PR gene expression is increased in spr9. These results demonstrate that Spr9 positively regulates JA signaling but negatively regulates SA signaling. Map based cloning studies reveal that Spr9 encodes an importin β like protein, which mediates import of nuclear localization signal (NLS)-containing cargo from the cytoplasm to the nucleus. In this application, we propose to elucidate the action mechanism of Tomato Spr9 gene in regulating systemin/jasmonate-mediated plant immunity. This study promises to shed new light on our understanding of the systemin/jasmonate signaling pathway and the antagonism between salicylate and jasmonate.

系统素和茉莉酸是番茄对病虫害防御反应过程中重要的信号分子，二者通过一个共同的信号转导途径调控植物对机械损伤和病虫侵害的抗性反应。我们长期以番茄为材料，从筛选spr (suppressor of prosystemin-mediated responses) 突变体入手，通过正向遗传学的手段解析系统素/茉莉酸信号转导途径。在spr9突变体中，受伤诱导的茉莉酸合成降低，抗性基因PI-II的表达下降，对昆虫的抗性降低，而对寄生型病原菌的抗性增强，水杨酸诱导的PR基因表达升高，说明Spr9正向调控茉莉酸途径而负向调控水杨酸途径。图位克隆结果表明Spr9编码importin β类转运蛋白，负责底物从细胞质向细胞核的运输。本申请拟通过深入分析Spr9的生物学功能，阐明Spr9在植物免疫反应中的作用机制，为进一步解析系统素/茉莉酸信号途径以及茉莉酸和水杨酸的相互拮抗关系提供创新性的知识积累。

番茄是研究系统性防御反应的经典模式植物，系统素和茉莉酸(JA)是番茄应对病虫害防御反应过程中的重要信号分子，二者通过共同的信号途径调控抗性反应。我们通过筛选spr (suppressor of prosystemin-mediated responses) 突变体，利用用正向遗传学的手段解析系统素/茉莉酸信号途径。本项目从Spr9基因编码Importin β类转运蛋白这一研究基础入手，通过酵母双杂交系统筛选Spr9互作蛋白，发现Spr9与转录调节因子Sip1互作。进一步研究发现，Spr7通过C端与Sip1具有核定位信号(Nuclear localization signal, NLS)的区域相互作用。通过分析Sip1-RNAi和Sip1-overexpression等转基因材料的表型，发现Sip1与Spr9相同，正向调控系统素/茉莉酸介导的防御反应而负向调控水杨酸介导的防御反应。Sip1蛋白既可以定位在细胞质中，也可以定位在细胞核中。但在spr9突变体背景下，Sip1蛋白在细胞核中的积累显著降低，表明Spr9影响Sip1从细胞质到细胞核中的转运。NLS区域定点突变试验表明，正常的细胞核定位对于转录调节因子Sip1的功能是至关重要的。综合分子遗传学、生物化学和细胞生物学等方法，我们推断Spr9通过介导Sip1转运至细胞核调控植物的免疫反应。.. 本项目通过正向遗传学筛选鉴定到植物免疫反应过程中差异性调控茉莉酸和水杨酸信号转导的新元件，并揭示出“核质转运”在植物免疫反应中的重要作用。本研究深化了我们对植物免疫信号转导调控机制的理解，同时为作物抗生物胁迫的分子育种提供了理论基础。