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Title: The mitogen-activated protein kinase gene, VdHog1, regulates osmotic stress response, microsclerotia formation and virulence in Verticillium dahliae

Author
item WANG, YONGLIN - Beijing Forestry University
item TIAN, LONGYAN - Beijing Forestry University
item XIONG, DIANGUANG - Beijing Forestry University
item Klosterman, Steven
item XIAO, SHUXIAO - Beijing Forestry University
item TIAN, CHENGMING - Beijing Forestry University

Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2016
Publication Date: 1/21/2016
Citation: Wang, Y., Tian, L., Xiong, D., Klosterman, S.J., Xiao, S., Tian, C. 2016. The mitogen-activated protein kinase gene, VdHog1, regulates osmotic stress response, microsclerotia formation and virulence in Verticillium dahliae. Fungal Genetics and Biology. 88:13–23.

Interpretive Summary: The soilborne fungus Verticilllium dahliae causes the disease Verticillium wilt on lettuce and other crops. The occurrence of Verticillium wilt disease is difficult to prevent on many crops, primarily because V. dahliae produces long-lived, darkly pigmented structures known as microsclerotia that enable this fungus to survive for more than 10 years in the soil. The survival of these spores in soil thus precludes the cultural practice of crop rotation as a means to manage this disease. Analysis of factors affecting the ability of this fungus to produce the long-lived microsclerotia may lead to control measures that are alternative to the use of fungicides or even plant resistance. In this study, the function of a particular gene in V. dahliae, VdHog1, was examined by gene knockout, and was determined important for normal microsclerotia production in this fungus. The Verticillium strain that lacked the normal copy of VdHog1 was reduced in its ability to produce microsclerotia in culture media. The linkage in V. dahliae of osmostress responses in this study with microsclerotia production warrants further investigation, since factors that change osmolarity may affect the long-term survival of V. dahliae.

Technical Abstract: The fungus Verticillium dahliae has gained worldwide notoriety as a destructive plant pathogen, causing vascular wilt diseases on diverse plant species. The fungus produces melanized resting bodies, known as microsclerotia that can survive for 15 years in the soil, and are thus critically important in its disease cycle. In spite its importance, the molecular mechanisms that underpin microsclerotia formation, survival, and germination remain poorly understood. In this study, we observed that deletion of VdHog1 ('VdHog1), encoding a homolog of a high-osmolarity glycerol (HOG) response mitogen-activated protein kinase, displayed decreased numbers of melanized microsclerotia in culture, heightened sensitivity to hyperosmotic stress, and increased resistance to the fungicide fludioxonil. Through RNA-Seq analysis in this study, we identified 221 genes differentially expressed in the 'VdHog1 strain. Interestingly, the expression levels of genes involved in melanin biosynthesis, as well as the hydrophobin gene VDH1, involved in the early stage of microsclerotia formation, were significantly decreased in the 'VdHog1 strains relative to the wild-type expression levels. The 'VdHog1 strains strains exhibited decreased virulence relative the wild type strain on smoke tree seedlings. These results indicate that VdHog1 regulates hyperosmotic stress responses in V. dahliae, and establishes the HOG1-mediated pathway as a target to further probe the upstream and downstream processes that regulate asexual development, including microsclerotia production, in this fungus.