Mutations in VMK1, a mitogen-activated protein kinase gene, affect microsclerotia formation and pathogenicity in Verticillium dahliae.

Verticillium dahliae is an important soil-borne fungal pathogen that causes vascular wilt diseases in a large variety of important crop plants. Due to its persistence in the soil, control of Verticillium wilt relies heavily on soil fumigation. The global ban on methyl bromide, a highly effective soil fumigant, poses an urgent need to develop alternative control measures against Verticillium wilt; and these might be more forthcoming with a better understanding of the molecular and cellular mechanisms that underpin the pathogenicity of V. dahliae. In this study, we assessed the role in growth, development, and pathogenicity of VMK1, a gene encoding a mitogen-activated protein (MAP) kinase (hence, Verticillium MAP Kinase 1). Disruption of VMK1 via Agrobacterium tumefaciens-mediated transformation, in two V. dahliae isolates, one from lettuce and the other from tomato, resulted in severely reduced virulence in diverse host plants, suggesting that VMK1 is essential for pathogenicity and that the MAP kinase-mediated signaling pathway has a conserved role in fungal pathogenicity. The vmk1 mutants also exhibited reduced conidiation and microsclerotia formation, suggesting that the gene is important for multiple cellular processes.

Cloning and targeted disruption, via Agrobacterium tumefaciens-mediated transformation, of a trypsin protease gene from the vascular wilt fungus Verticillium dahliae.

A gene encoding a trypsin protease was isolated from a tomato isolate of Verticillium dahliae. The gene, designated VTP1, contains two introns and is predicted to encode a protein of 256 amino acids. The gene is present in V. dahliae isolates from different host plants and in V. albo-atrum; weakly hybridizing sequences are present in V. tricorpus. VTP1 cDNA sequences were identified in a sequence tag analysis of genes expressed under growth conditions that promote microsclerotia development. Replacement of the gene, by Agrobacterium tumefaciens-mediated transformation (ATMT), with a mutant allele construct did not noticeably alter either pathogenicity or growth in culture. Searches of expressed sequence tag databases showed that, in addition to the VTP1 gene, V. dahliae contains two genes encoding subtilisin-like proteases similar to those produced by pathogenic Aspergillus spp. This is the first description of the application of ATMT to the molecular analysis of phytopathogenic Verticillium spp.