Transcription factor VdCmr1 is required for pigment production, protection from UV irradiation, and regulates expression of melanin biosynthetic genes in Verticillium dahliae

Authors: WANG, YONGLIN - Beijing Forestry University; HU, XIAOPING - Northwest Agricultural & Forestry University; FANG, YULIN - Beijing Forestry University; Anchieta, Amy; Goldman, Polly; HERNANDEZ, GUSTAVO - Former ARS Employee; Klosterman, Steven

Submitted to: Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2018
Publication Date: 3/2/2018
Citation: Wang, Y., Hu, X., Fang, Y., Anchieta, A.G., Goldman, P.H., Hernandez, G., Klosterman, S.J. 2018. Transcription factor VdCmr1 is required for pigment production, protection from UV irradiation, and regulates expression of melanin biosynthetic genes in Verticillium dahliae. Microbiology. 164(4):685-696. https://doi.org/10.1099/mic.0.000633.
DOI: https://doi.org/10.1099/mic.0.000633

Interpretive Summary: Long-term survival of soil borne fungal plant pathogens, such as the fungus Verticillium dahliae, is dependent on the production of long-term survival structures (microsclerotia) that are usually heavily pigmented. This type of pigmentation is also referred to as melanization. In this research, we analyzed three genes within a melanin biosynthetic gene cluster in Verticillium dahlaie for their roles in melanin production, microsclerotia production, pathogenicity, and also regulation of other genes in the gene cluster. Two these genes examined by mutational analyses were required for melanin production, but not microsclerotia production, while a separate third gene was not required for melanin or microsclerotia production. One of the genes is regulatory, and controls the expression of other genes in this melanin biosynthetic cluster. None of the three genes was required for pathogenicity. Insights on the genetic and molecular mechanisms that underlie the development of the survival structures of Verticillium can be useful to develop alternative disease control strategies that target this broad host range pathogen, and related pathogenic fungi, in the soil.

Technical Abstract: Verticillium dahliae is a soilborne fungus that causes vascular wilt diseases on numerous plant species worldwide. The production of darkly melanized microsclerotia is crucial in the disease cycle of V. dahliae, as these structures allow for long-term survival in soil. Previously, transcriptomic and genomic analysis identified a cluster of genes in V. dahliae that encodes some dihydroxynaphthalene (DHN) melanin biosynthetic pathway homologs found in related fungi. In this study, we explored roles of cluster-specific transcription factor VdCmr1, as well as two other genes within the cluster encoding a polyketide synthase (VdPKS1) and a laccase (VdLac1), enzymes at the initial and endpoint steps in DHN melanin production. The results revealed that VdCmr1 and VdPKS1 are required for melanin production, but neither is required for microsclerotia production. None of the three genes was required for pathogenesis on tobacco and lettuce. Exposure of 'VdCmr1 and wild type strains to UV irradiation, or to high temperature (40o C), revealed an approx. 50% reduction of survival in the 'VdCmr1 strain, relative to the wild type strain, in response to either condition. Expression profiles revealed that expression of some melanin biosynthetic genes are in part dependent on VdCmr1. Combined data indicate VdCmr1 is a key regulator of melanin biosynthesis, and that via regulation of melanogenesis, VdCmr1 affects survival of V. dahliae in response to abiotic threats. We conclude with a model showing regulation of VdCmr1 by a high osmolarity glycerol response (Hog)-type MAP kinase pathway.