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MgHog1 Regulates Dimorphism and Pathogenicity in the Fungal Wheat Pathogen Mycosphaerella graminicola

November 2006 , Volume 19 , Number  11
Pages  1,262 - 1,269

Rahim Mehrabi , 1 , 2 Lute-Harm Zwiers , 3 Maarten A. de Waard , 4 and Gert H. J. Kema 1

1Plant Research International B.V., Wageningen University and Research Centre (WUR), P.O. Box 16, 6700 AA, Wageningen, The Netherlands; 2Seed and Plant Improvement Institute, Agricultural Research and Education Organization, PO Box 31585-4119, Karaj, Iran; 3Centraalbureau voor Schimmelcultures, Uppsalalaan 8, 3584CT Utrecht, The Netherlands; 4Laboratory of Phytopathology, WUR, Binnenhaven 5, 6709 PD, Wageningen, The Netherlands


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Accepted 20 June 2006.

The dimorphic ascomycete pathogen Mycosphaerella graminicola switches from a yeastlike form to an infectious filamentous form that penetrates the host foliage through stomata. We examined the biological function of the mitogen-activated protein kinase-encoding gene MgHog1 in M. graminicola. Interestingly, MgHog1 mutants were unable to switch to filamentous growth on water agar that mimics the nutritionally poor conditions on the foliar surface and, hence, exclusively developed by a yeastlike budding process. Consequently, due to impaired initiation of infectious germ tubes, as revealed by detailed in planta cytological analyses, the MgHog1 mutants failed to infect wheat leaves. We, therefore, conclude that MgHog1 is a new pathogenicity factor involved in the regulation of dimorphism in M. graminicola. Furthermore, MgHog1 mutants are osmosensitive, resistant to phenylpyrrole and dicarboximide fungicides, and do not melanize.


Additional keywords: Agrobacterium tumefaciens-mediated transformation , differentiation , transposon , virulence .

© 2006 The American Phytopathological Society