Trihelix家族转录因子调控植物先天免疫的分子机理

Sessile plants largely rely on the innate immune system to launch prompt defense responses to fend off potential infections. Pattern-triggered immunity (PTI) is the first layer of plant immunity. Perception of pathogen-associated molecular patterns (PAMPs) by cell surface-resident pattern recognition receptors (PRRs) induces rapid immune responses and robust transcriptional reprogramming, which is central for launching effective PTI in plants. It remains largely unknown that the mechanisms of gene transcription regulation in plant immune responses. Previously, we showed that ARABIDOPSIS SH4-RELATED 3 (ASR3), a transcriptional factor belonging to the Trihelix family SH4 clade, functions as a transcriptional repressor and plays a negative role in regulating PTI in Arabidopsis thaliana. ASR3 is phosphorylated by MPPK4 upon PAMPs treatment and fine-tunes plant immune gene expression by the transcriptional suppression function. In this proposal, we plant to study the formation and biological relevance of hetero-dimerization between ASR3 and other members in Trihelix family. The second object is the identification of target genes which are directly regulated by ASR3 and the specific DNA sequence bound by ASR3. We will also examine whether other members in SH4 clade are involved in PTI responses. Our study will extend the knowledge of regulation mechanisms underlying gene expression during plant PTI. It will also help to understand how Trihelix family transcriptional factors play roles in the immune gene expression and explain the interaction, interfere or redundancy between different transcriptional factors. Further, our study likely will provide new gene recourses for genetic modification of crop resistance against pathogenic bacteria.

植物抵御有害微生物入侵主要依赖其先天免疫系统，病原相关分子模式诱导的免疫反应是植物第一层次的免疫反应，由位于植物细胞表面的模式受体蛋白识别病原菌相关分子模式而触发，迅速诱导多种免疫反应和表达谱的强烈改变。免疫相关基因及时和准确地表达是抗病的关键步骤，但是调控免疫基因转录的分子机理还不清楚。前期研究我们发现了拟南芥Trihelix家族SH4分支转录因子ASR3反向调控植物PTI免疫反应基因的表达。本项目拟研究ASR3与其同家族蛋白异源二聚体的形成及其生物学意义，鉴定受ASR3直接调控的免疫相关基因，并详细分析ASR3结合DNA序列特征，同时明确SH4分支其它成员的生物功能。项目的完成将丰富对植物PTI免疫相关基因表达调控的认知，更加全面阐述Trihelix家族成员在PTI免疫反应中发挥作用的分子机制，解释不同转录因子间的互作或冗余关系，也有可能为抗病育种提供新的基因资源。

植物在长期与病原微生物协同进化过程中，形成了复杂且精细的免疫系统来抵御病原菌的入侵。植物通过感知微生物相关分子模式诱导快速的免疫反应和转录重编程。前期研究发现拟南芥trihelix家族SH4分支转录因子ASR3作为转录抑制因子，受到MAMP激活的MPK4磷酸化，进而反向调控植物免疫基因的表达。在本项目中，通过鉴定筛选到的ASR3的互作因子AITF1的功能，解析ASR3和AITF1在调控植物抗病反应中的相互关系以及二者的靶标基因，以此丰富了Trihelix家族转录因子在植物抗病中的功能。首先，通过多种蛋白质互作实验证明二者在体内体外是互作的，并发现ASR3的N端、C端和AITF1的C端参与二者的互作，并且ASR3和AITF1形成异源或同源二聚体。其次，发现AITF1超量表达和敲除增强植物对病原细菌的抗性，然而aitf1 asr3双敲除突变体可以恢复单突变体的抗性增强表型，说明二者功能相互依赖；研究也发现了AITF1的超量表达引起植物自我免疫而且完全依赖于ASR3。再次，探究了二者介导的自我免疫和细胞死亡依赖TNL类型抗病基因下游的EDS1相关的信号途径，进而通过转录组和ChIP数据联合分析，筛选到了ASR3自我免疫是因为激活了SAA1基因的表达，生化实验证明ASR3和AITF1通过结合TNL基因SAA1启动子并激活该基因的表达，促进植物产生过度免疫和细胞坏死。最后，本研究也揭示了SH4分支的HDP2蛋白也参与植物免疫反应，并探究了该蛋白所介导的组蛋白乙酰化和DNA去甲基化途径调控免疫基因表达的分子机制。通过本项目的研究丰富了Trihelix家族转录因子调控植物免疫反应的分子机制，并为深入研究植物NLRs基因表达调控机制提供了新的线索。