禾谷镰刀菌DON毒素合成相关G蛋白偶联受体的作用机理

禾谷镰刀菌引起的赤霉病不仅是小麦上的重大致灾病害，而且产生的DON毒素严重威胁人畜健康。已知在禾谷镰刀菌侵染早期即可检测到DON合成基因的表达，然而禾谷镰刀菌如何识别宿主信号并启动DON合成的机制仍不清楚。G蛋白偶联受体（GPCR）是负责信号识别的重要膜受体和药物靶标，项目前期通过敲除禾谷镰刀菌85个GPCR基因，鉴定到其中3个与DON合成相关（G6、G22和G59）。我们拟对这3个DON合成相关GPCR以及与它们在序列和表达模式上类似的GPCR进行多基因敲除，分析这些GPCR在DON合成中的功能及相互关系，并明确其介导的下游信号通路。为了研究DON合成相关GPCR在寄主信号识别中的作用，我们将从寄主组织中分离并筛选出DON合成诱导物，进一步确定病原真菌GPCR和寄主信号物质的对应关系。研究结果对明确禾谷镰刀菌的寄主识别和产毒调控机制具有重要价值，为防治小麦赤霉病毒素污染提供候选药物靶标。

Fusarium head blight (FHB) caused by Fusarium graminearum is one of the most destructive diseases of wheat. In addition to severe yield losses and grain quality reduction, F. graminearum produces trichothecene mycotoxin deoxynivalenol (DON) in infested grains which is harmful to human health. Trichothecene (TRI) synthesis gene expression was detected as early as 12 hpi in infection cushions or penetration pegs. However, it remains unclear how F. graminearum recognizes signals from the host to regulate DON biosynthesis. G protein-coupled receptors (GPCRs) are considered to be important for signal recognition. In the preliminary study, we functionally characterized all the 85 GPCR genes and found three of them were important for DON production. In this study, we aim to further characterize the role of these three GPCR genes in DON synthesis and identify their downstream signal transduction pathways. Regarding functional redundancy between GPCRs, we will characterize their functional relationship by generating double or triple mutants and mutants deleted of multiple GPCR genes with similar expression profiles or structures with these three GPCRs, then assayed for their defects in DON biosynthesis. To determine the roles of these three GPCRs in the recognition to host-derived signals, we will assay for their functions in the recognition of known DON inducing plant compounds and other novel DON-stimulating factors in wheat floral tissues. The specific ligand-receptor relationship between a fungal GPCR and a DON inducing host factor will be further characterized with the yeast expression system. Overall, results from the proposed project will not only improve our understanding of host recognition and DON regulation, but also lead to the development of novel strategies for reducing mycotoxin contamination in wheat.