Abstract
The soil-borne ascomycete fungus Verticillium dahliae causes vascular wilt disease and can seriously diminish the yield and quality of important crops. Functional analysis of growth- and pathogenicity-related genes is essential for revealing the pathogenic molecular mechanism of V. dahliae. Phospholipase is an important virulence factor in fungi that hydrolyzes phospholipids into fatty acid and other lipophilic substances and is involved in hyphal development. Thus far, only a few V. dahliae phospholipases have been identified, and their involvement in V. dahliae development and pathogenicity remains unknown. In this study, the function of the patatin-like phospholipase gene in V. dahliae (VdPLP, VDAG_00942) is characterized by generating gene knockout and complementary mutants. Vegetative growth and conidiation of VdPLP deletion mutants (ΔVdPLP) were significantly reduced compared with wild type and complementary strains, but more microsclerotia formed. The ΔVdPLP mutants were very sensitive to the cell-wall-perturbing agents: calcofluor white (CFW) and Congo red (CR). The transcriptional level of genes related to the cell wall integrity (CWI) pathway and chitin synthesis were downregulated, suggesting that VdPLP has a pivotal role in the CWI pathway and chitin synthesis in V. dahliae. ΔVdPLP strains were distinctly impaired in in their virulence and ability to colonize Nicotiana benthamiana roots. Our results demonstrate that VdPLP regulates hyphal growth and conidial production and is involved in stabilizing the cell wall, thus mediating the pathogenicity of V. dahliae.
Highlights
Verticillium dahliae, a soil-borne, filamentous fungal plant pathogen with wide distribution around the world, can attack many important crops such as cotton, soybean, potato, sugar beet and sunflower, causing significant crop losses annually [1,2]
Strains was significantly smaller than that of the colony on PDA without Congo red (CR). These results indicated that ∆VdPLP strains were more sensitive to CR and calcofluor white (CFW) than the wild type and complementary strains, and VdPLP was responsible for maintaining fungal cell wall integrity in V. dahliae
To further confirm that VdPLP contributes to the cell wall integrity (CWI) pathway and chitin synthesis, we focused on the regulation of the CWI pathway by profiling transcript levels of the CWI pathway genes VdMKK1 and VdMK1 and chitin synthesis genes VdChi1, VdChi3, VdChi4, and VdChi7
Summary
Verticillium dahliae, a soil-borne, filamentous fungal plant pathogen with wide distribution around the world, can attack many important crops such as cotton, soybean, potato, sugar beet and sunflower, causing significant crop losses annually [1,2]. It is a significant threat to cash-crop production. It produces microsclerotia, dormant structures that can survive for many years in the soil and be induced to germinate by plant root exudates [3,4]. Hyphae colonize the plant root surface, and form a narrow penetration peg that can penetrate the epidermal cells [5]. Hyphae grow intracellularly and intercellularly through the root cortex, enter the xylem vessels and colonize the xylem of the hypocotyl and leaves. The molecular mechanisms underlying V. dahliae pathogenesis are complex and still not clear [4,5,6,7,8], so functional analyses of growth- and pathogenicity-related genes are crucial in developing new strategies to control V. dahliae
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