Verticillium dahliae Vta3 promotes ELV1 virulence factor gene expression in xylem sap, but tames Mtf1-mediated late stages of fungus-plant interactions and microsclerotia formation

Verticillium transcription activator of adhesion 3 (Vta3) is required for plant root colonization and pathogenicity of the soil-borne vascular fungus Verticillium dahliae [Bui et al., 2018]. In this study, we discovered that Vta3 contributes to the virulence of V. dahliae on tomato plants by promoting ELV1 gene expression, which is not necessary for vegetative growth or production of conidiospores. Gene expression of the transcription factor Mtf1 is reduced in the presence of an intact VTA3 gene. The presence of an intact MTF1 gene triggers the expression of fungal effector genes and plant immune responses (transcription of tomato pathogenesis-related protein genes, and levels of pipecolic and salicylic acids functioning in tomato defense signaling against (hemi-) biotrophic pathogens), and is required for disease symptoms similar to those seen in tomato plants infected by the V. dahliae wild-type. Mtf1 promotes the formation of resting structures at the end of the infection cycle, which allows the fungus to survive in the soil and later to re-infect host plants. Protein pull-downs were performed with GFP-fused Vta3 to investigate whether there is evidence for a direct interaction of the regulators Vta3 and Mtf1. In this study, ribosomal proteins predominantly co-enriched with Vta3, and our data set did not give evidence that Mtf1 directly interacts with Vta3. Bui T-T, Harting R, Braus-Stromeyer SA, Tran V-T, Leonard M, Höfer A, et al. Verticillium dahliae transcription factors Som1 and Vta3 control microsclerotia formation and sequential steps of plant root penetration and colonisation to induce disease. New Phytologist. 2019;221: 2138–2159. doi:10.1111/nph.15514

黏附转录激活因子3（Verticillium transcription activator of adhesion 3, Vta3）是土传维管束真菌大丽轮枝菌（Verticillium dahliae）定殖植物根系并发挥致病性所必需的调控因子[Bui等, 2018]。本研究发现，Vta3可通过促进ELV1基因的表达增强大丽轮枝菌对番茄植株的致病力，该过程无需依赖真菌的营养生长与分生孢子产生。在完整VTA3基因存在的条件下，转录因子Mtf1的基因表达水平显著下调。完整MTF1基因的存在则会触发真菌效应因子基因的表达与植物免疫应答，包括番茄病程相关蛋白（PR）基因的转录，以及参与番茄抗（半）活体营养型病原菌防御信号通路的哌啶酸与水杨酸水平调控，且该基因对于诱导出现与野生型大丽轮枝菌侵染番茄植株相似的病害症状是必需的。Mtf1还可促进侵染周期末期休眠结构的形成，帮助真菌在土壤中存活并于后续重新侵染寄主植物。为探究调控因子Vta3与Mtf1是否存在直接相互作用，本研究采用绿色荧光蛋白（Green Fluorescent Protein, GFP）融合的Vta3开展蛋白质下拉实验。结果显示，本研究中与Vta3共富集的蛋白以核糖体蛋白为主，且本数据集未提供Mtf1与Vta3存在直接相互作用的证据。

Bui T-T, Harting R, Braus-Stromeyer SA, Tran V-T, Leonard M, Höfer A, 等. 大丽轮枝菌转录因子Som1与Vta3调控微菌核形成及植物根系侵染与定殖的时序步骤以诱导病害发生. 新植物学家（New Phytologist）. 2019;221: 2138–2159. doi:10.1111/nph.15514