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

Yonglin Wang,Steven J Klosterman,Polly H Goldman,Xiaoping Hu,Amy Anchieta,Yulin Fang,Gustavo Hernandez

doi:10.1099/mic.0.000633

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 homologues found in related fungi. In this study, we explored the 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 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 were required for pathogenesis on tobacco and lettuce. Exposure of ΔVdCmr1 and wild-type strains to UV irradiation, or to high temperature (40 °C), revealed an approx. 50 % reduction of survival in the ΔVdCmr1 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.

Highlights

The fungus Verticillium dahliae causes economically important vascular wilt diseases on more than 200 plant species worldwide [1]
The results showed that VdCmr1 is required for melanin biosynthesis and microsclerotia formation, and that VdCmr1 regulates expression of genes scattered throughout the genome of V. dahliae that are associated with melanin biosynthesis
Our study expands the understanding of the genetics of melanin biosynthesis, its regulation and its relationship to virulence in V. dahliae

Summary

Introduction

The fungus Verticillium dahliae causes economically important vascular wilt diseases on more than 200 plant species worldwide [1]. The list of plant species affected by V. dahliae is continually expanding as new hosts are identified [2]. V. dahliae is difficult to control, owing in part to the production of melanized resting structures, known as microsclerotia, which can survive for years in the soil [3]. Fungal dihydroxynaphthalene (DHN) melanin is composed of polymerized phenolic or indolic compounds, and its biosynthesis was originally discovered in V. dahliae [4]. DHNmelanin biosynthesis begins with a polyketide synthase (PKS) that catalyses the conversion of acetyl-CoA to 1,3,6,8tetrahydroxynaphthalene (1,3,6,8-THN). Through a series of downstream reactions catalysed by reductases and dehydratases, 1,8-DHN is produced [4,5,6]

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