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Title: Characterization of two homeodomain transcription factors with critical but distinct roles in virulence in the vascular pathogen Verticillium dahliae

item SARMIENTO-VILLAMIL, JORGE - University Of Malaga
item PRIETO, PILAR - Institute For Sustainable Agriculture
item Klosterman, Steven
item GARCIA-PEDRAJAS, MARIA - University Of Malaga

Submitted to: Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/2017
Publication Date: 7/20/2017
Citation: Sarmiento-Villamil, J.L., Prieto, P., Klosterman, S.J., Garcia-Pedrajas, M.D. 2017. Characterization of two homeodomain transcription factors with critical but distinct roles in virulence in the vascular pathogen Verticillium dahliae. Molecular Plant Pathology.

Interpretive Summary: Verticillium dahliae is soilborne fungal pathogen that causes Verticillium wilt diseases on economically important crops and ornamental plants worldwide. A better understanding of the genetics that control how this pathogen is able to develop and cause disease on plants is anticipated to provide insights into new or novel Verticillium wilt control measures. In this study, two genes that encode regulatory proteins were deleted in Verticillium dahliae, and the strains were examined to determine how these genes function during development of disease. The results revealed that neither strain caused disease symptoms in plants, with one of the strains being defective in its ability to penetrate the plant, and the other incapable of proliferation in the plant once infection had taken place. Global gene expression analyses of both of the mutant strains revealed that both of the genes regulate large subsets of genes in the fungus. These genes are targets for further identifying the genes of Verticillium dahliae that are important for pathogenic development, and particularly those that may be important for early stage of infection.

Technical Abstract: Vascular wilt caused by Verticillium dahliae is a destructive disease that represents a chronic economic problem for crop production worldwide. In this work, we characterized two new regulators of pathogenicity in this species. Vph1 (VDAG_06555) was identified in a candidate gene approach as a putative homologue of the transcription factor Ste12. Vhb1 (VDAG_08786), identified in a forward genetics approach, is similar to the homeobox transcription factor Htf1, reported as a regulator of conidiogenesis in several fungi. Deletion of vph1 did not affect vegetative growth, whereas deletion of vhb1 greatly reduced sporulation rates in liquid medium. Both mutants failed to induce Verticillium wilt symptoms. However, unlike 'vph1, 'vhb1 could be re-isolated from the vascular system of some asymptomatic plants. Confocal microscopy further indicated that 'vph1 and 'vhb1 differed in their behaviour in planta; 'vph1 could not penetrate the root cortex, whereas 'vhb1 was impaired in its ability to colonize the xylem. In agreement with these observations, only 'vhb1 could penetrate cellophane paper. On cellophane, wild-type and 'vhb1 strains produced numerous short branches with swollen tips, resembling the hyphopodia formed on root surfaces, contrasting with 'vph1, which generated unbranched long filaments without swollen tips. A microarray analysis showed that these differences in growth were associated with differences in global transcription patterns, and allowed us to identify a large set of novel genes potentially involved in virulence in V. dahliae. Ste12 homologues are known regulators of invasive growth, but Vhb1 is the first putative Htf1 homologue identified with a critical role in virulence.