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Fig. 7 | BMC Biology

Fig. 7

From: A polyketide synthase from Verticillium dahliae modulates melanin biosynthesis and hyphal growth to promote virulence

Fig. 7

VdPKS9 colludes with VdPKS1 to contribute to pathogenicity of Verticillium dahliae. A, C Pathogenicity assay of the indicated strains on cotton and tobacco. Cotton (A) and tobacco (C) seedlings were mock inoculated (Mock) or inoculated with wild-type strain AT13 (WT), VdPKS9 deletion strains (ΔVdPKS9), VdPKS1 deletion strains (ΔVdPKS1), and double deletion of VdPKS9 and VdPKS1 strains (ΔVdPKS9_1), and the Verticillium wilt symptom (top) were photographed at 21 and 14 dpi on cotton (with addition phenotype of vascular discoloration) and tobacco, respectively. B, D Quantification the fungal biomass in plant shoots by quantitative PCR following inoculation of the indicated strains. Cotton (B) and tobacco (D) shoot samples were collected from the stem base of plants at 21 dpi. The V. dahliae elongation factor 1-α (EF-1α) was used to quantify fungal colonization, and the cotton 18S gene and tobacco NbEF-1α served as an endogenous plant control. The experiment was replicated three times. The pathogenicity was analyzed with three replicates of 20 cotton and 6 tobacco plants, and the fungal biomass was calculated by three independent biological replicates. Error bars represent standard errors. ***P < 0.001 (one-way ANOVA). E–G Pathogenicity assay of transformants overexpressing VdPKS9 in the wild-type strain AT13. Cotton seedlings were mock-inoculated (Mock) or inoculated with wild-type strain AT13 (WT) and VdPKS9 overexpressing transformant and evaluated by pathogenicity indexes at 21 dpi, included foliar Verticillium wilt symptoms (top) and vascular discoloration. E Fungal biomass development (F) and the disease index (G). The disease index was analyzed with three replicates of cotton pathogenicity tests. H Pathogenicity assay of the AH-type and MH-type strains during infection of cotton plants. In total, 37 AH-type strains and 34 MH-type strains were selected for virulence analysis by root-dip method on cotton plant, and disease indices were evaluated at 28 dpi. I Analyses of the pathogenicity characteristics of AH-type and MH-type strains. Polynomial fitting was employed. J The relative expression of VdPKS9 in AH-type and MH-type strains infecting and colonizing cotton plants. RNA of samples collected from 0 to 18 dpi was extracted and reverse transcribed. The expression levels were calculated by RT-qPCR in three replicate experiments. Error bars represent standard errors, *P < 0.01, **P < 0.01, and ***P < 0.001 (one-way ANOVA). K A working model showing VdPKS9 colludes with VdPKS1 to contribute to pathogenicity of Verticillium dahliae. The V. dahliae PKS member VdPKS9 functions in an unknown SM pathway that participates in the maintenance of hyphal growth, and thus promotes the pathogenicity. Another PKS, VdPKS1, functions in melanin biosynthesis and accelerates hyphae melanization, a function negatively regulated by VdPKS9. Broadly, V. dahliae networks the two PKSs of VdPKS9 and VdPKS1 to contribute to pathogenicity by suppressing MS and melanin production and promoting hyphal growth. This represents the potential mechanism by which the AH-type strains display stronger virulence than MH-type strains in V. dahliae

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