EC Accepts, published online ahead of print on 1 May 2009

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Eukaryotic Cell doi:10.1128/EC.00258-08
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

G and G proteins regulate the cAMP pathway that is required for development and pathogenicity of the phytopathogen Mycosphaerella graminicola

Rahim Mehrabi, Sarrah Ben M'Barek, Theo A.J. van der Lee, Cees Waalwijk, Pierre J. G. M. de Wit, and Gerrit H. J. Kema^*

Plant Research International B.V., Wageningen University and Research Centre (WUR), P.O. Box 16, 6700 AA, Wageningen, The Netherlands; Laboratory of Phytopathology, WUR, Binnenhaven 5, 6709 PD, Wageningen, The Netherlands

^* To whom correspondence should be addressed. Email: gert.kema{at}wur.nl.

We identified and functionally characterized genes encoding three G proteins and one G protein in the dimorphic fungal wheat pathogen Mycosphaerella graminicola, which we designated MgGpa1, MgGpa2, MgGpa3 and MgGpb1, respectively. Sequence comparisons and phylogenetic analyses showed that MgGPA1 and MgGPA3 are most related to the mammalian G_i and G_s families, respectively, whereas MgGPA2 is not related to either of these two families. On PDA and in yeast glucose broth (YGB), MgGpa1 mutants produced significantly longer spores than the WT, that developed into unique fluffy mycelia in the latter medium, indicating that this gene negatively controls filamentation. MgGpa3 mutants showed more pronounced yeast-like growth accompanied with hampered filamentation and secreted a dark-brown pigment into YGB. Germ tubes emerging from spores of MgGpb1 mutants were wavy on water agar (WA) and showed a nested-type of growth on PDA that was due to hampered filamentation, numerous cell fusions and increased anastomosis. Intracellular cAMP levels of MgGpb1 and MgGpa3 mutants were decreased indicating that both genes positively regulate the cAMP pathway, which was confirmed as the WT phenotype was restored by adding cAMP to these mutant cultures. The cAMP levels in MgGpa1 mutants and the WT were not significantly different, suggesting that this gene might be dispensable for cAMP regulation. In planta assays showed that mutants of MgGpa1, MgGpa3 and MgGpb1 are strongly reduced in pathogenicity. We conclude that the heterotrimeric G proteins MgGpa3 and MgGpb1 regulate the cAMP pathway that is required for development and pathogenicity in M. graminicola.