FgAtm1-FgHapX途径调控禾谷镰刀菌铁平衡的机制研究

Fusarium graminearum complex as an economically important plant pathogen causes Fusarium head blight (FHB) on various cereal crops. Moreover, mycotoxins produced by the pathogen seriously threaten the health of human and animal. In recent years, wheat and rice were rotated in the middle and lower reaches of the Yangtze River and the regions of Jianghuai. However high iron toxicity did not affect the survival of F. graminearum in fields that were flooded. In our previous study, we found that F. graminearum displays increased tolerance to iron stress than other fungi and only FgAtm1 out of the 60 ABC transporters is involved in the regulation of iron homeostasis. Further studies showed that FgATM1 deletion caused intracellular iron accumulation, FgHapX controlled the transcription of iron-related genes that is responsive to FgAtm1 absence, the phosphorylation and interacting protein FgGrx4 is required for FgHapX function in iron homeostasis. Based on these previous results, this study will uncover the regulatory mechanism of iron homeostasis mediated by FgAtm1-FgHapX in F. graminearum, investigate the functions of the phosphorylation of FgHapX and FgGrx4 in modulating iron homeostasis, and explore the biological functions of iron homeostasis for F. graminearum. We expect that this study will provide a novel insight for regulation of iron homeostasis in eukaryotes and a new strategy for controlling the initial F. graminearum source in fields.

小麦赤霉病及其病菌产生的真菌毒素严重威胁我国小麦生产和农产品质量安全。长江中下游和江淮稻麦轮作区，淹水稻田的土壤中易产生还原态铁离子（Fe2+），但没有对禾谷镰刀菌产生铁毒害，水旱轮作不影响病菌在土壤中的存活能力。项目前期研究发现，禾谷镰刀菌比常见真菌对铁胁迫有更强的适应性，且60个ABC蛋白中仅FgAtm1对铁胁迫超敏感。研究又发现FgAtm1缺失导致细胞内铁积累；FgHapX响应FgAtm1调控铁相关基因表达；FgHapX功能依赖两个位点的磷酸化；FgGrx4作为FgHapX的互作蛋白共同调控铁平衡。在此基础上，拟深入研究FgAtm1-FgHapX途径调控禾谷镰刀菌中铁平衡的分子机制，解析FgHapX磷酸化对其功能的影响，阐述FgHapX与FgGrx4互作的生物学意义，分析铁平衡在禾谷镰刀菌中的生物学功能。预期结果为真核生物中铁平衡调控提供新视点，为控制禾谷镰刀菌初菌源菌量提供新思路。

本研究通过基因功能研究、表达谱分析、ChIP-qPCR、蛋白互作技术解析了禾谷镰刀菌中铁动态平衡的调控机制。本研究发现禾谷镰刀菌中，细胞内的二价铁进入线粒体加工成铁硫簇后，通过定位在线粒体膜上的ABC蛋白FgAtm1输出，输出的铁硫簇被谷氧还蛋白结合，参与铁硫蛋白的合成。FgAtm1缺失后，细胞质中次级氮源利用蛋白得不到铁硫供应，活性降低，反向激活次级氮源利用调控因子FgAreA在铁转录因子FgHapX启动子区富集，进一步激活FgHapX的转录活性，导致细胞内铁积累。转录调控因子FgHapX抑制铁利用基因和FgSreA表达；FgSreA抑制铁吸收基因表达。谷氧还蛋白FgGrx4协助FgHapX调控了铁的动态平衡，而且S245和S338位点的磷酸化调控FgHapX的转录活性。酵母中Atm1主要通过下游的转录因子Aft1调控铁动态平衡，而丝状真菌中没有Aft1同源物。本研究阐明FgAtm1通过转录因子级联FgAreA-HapX调控铁动态平衡的新机制，报道氮源代谢与铁代谢之间的关联性，为真菌中铁的代谢调控提供新视点。