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

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.

Insights into VdCmr1‐mediated protection against high temperature stress and UV irradiation in Verticillium dahliae

“…Both in response to UV irradiation and HT, a significant reduction in survival was observed in the △ VdCmr1 strain in comparison to the wild‐type strain VdLs.17 (Wang et al ., ). But we had previously not examined the expression of VdCmr1 in response to these stresses.…”

“…The role of the Cmr1 homologue, CmrA, in Alternaria alternata controls the expression of at least three structural genes ( brm1 , brm2 and pksA ), each of which is required for the melanin biosynthesis (Fetzner et al ., ). Previously, we showed that VdCmr1 is a key regulator of melanin biosynthesis (Wang et al ., ). While Δ VdCmr1 strains of V. dahliae show significantly lower survival rates than the wild‐type strain VdLs.17 in response to UV irradiation and HT (Wang et al ., ), the protective mechanism that VdCmr1 imparts to V. dahliae in response to HT stress or UV irradiation remains unclear.…”

“…Previously, we showed that VdCmr1 is a key regulator of melanin biosynthesis (Wang et al ., ). While Δ VdCmr1 strains of V. dahliae show significantly lower survival rates than the wild‐type strain VdLs.17 in response to UV irradiation and HT (Wang et al ., ), the protective mechanism that VdCmr1 imparts to V. dahliae in response to HT stress or UV irradiation remains unclear.…”

The Verticillium dahliae Sho1‐MAPK pathway regulates melanin biosynthesis and is required for cotton infection

“…In contrast, analyses of two deletion mutants of either VdPKS1 or VdCmr1 within the melanin biosynthetic gene cluster in V . dahliae strain VdLs.17 revealed that neither was required for full virulence on lettuce and tobacco, but were required for survival in response to UV irradiation and high‐temperature stress (Wang et al ., ). Additionally, melanin accumulation was not necessary for pathogenicity of Δ Vst1 strains of V .…”

“…Albino mutants or strains, which produce microsclerotia and lack typical pigmentation or that are hyaline, are commonly characterized in V . dahliae , yet are pathogenic (Daayf et al ., ; Wang et al ., ). Taken together, this suggests a complex interplay between signalling mechanisms controlling melanin production and virulence in V .…”