10th INTERNATIONAL VERTICILLIUM SYMPOSIUM 16-20 ...

CATALYTIC SUBUNIT OF PROTEIN KINASE A INVIRULENCE AND PHYSIOLOGY OF VERTICILLIUM DAHLIAEA. TZIMA 1 , E. J. PAPLOMATAS 1 , D. I. TSITSIGIANNIS 1 AND S. KANG 21 Department of Plant Pathology, Agricultural University of Athens, 75 Iera Odos, 11855 Athens,Greece;2Department of Plant Pathology, The Pennsylvania State University, University Park, PA 16802, USAG proteins transduce external signals to intracellular targets, regulatingcellular and developmental processes, and also affect virulence in several plantpathogenic fungi. Mitogen-activated protein kinase (MAPK) and cAMP dependentsignaling cascades have been implicated as downstream targets of G proteins infilamentous fungi. The major downstream protein implicated in the cAMP-dependentsignaling pathway is the cAMP-dependent protein kinase A (PKA). To gain insightinto the role of the cAMP-dependent signaling pathway in virulence and developmentof the soilborne, wilt causing fungus Verticillium dahliae, the G protein β subunit(VdGb) and the PKA (VdPKAC1) genes were individually disrupted in tomato race 1strain of V. dahliae through gene replacement. Deletion mutants (70ΔGb and70ΔPKA) showed reduced virulence, which was more drastic in the Gb mutants asthey caused almost no visible symptoms. Moreover, disruption of the Gb orVdPKAC1 gene caused induction of microsclerotia production, increase ingermination and decrease in ethylene production compared to the wild type strain.Similar to virulence, the change in these phenotypes was more prounced in 70ΔGbthan in 70ΔPKA. In addition, 70ΔGb mutants presented a vertical rather a radialgrowth pattern on agar media. Overexpression of PKA in 70ΔGb mutant restored theradial wild type growth, germination and conidiation. Mutants were unable to producesclerotia, but were able to cause typical disease symptoms on tomato plants. Thefindings of the present work suggest interaction between Gb and PKA in regulatingvirulence, physiology and development in V. dahliae.51