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Eukaryotic Cell, July 2009, p. 1001-1013, Vol. 8, No. 7
1535-9778/09/$08.00+0     doi:10.1128/EC.00258-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

G{alpha} and Gβ Proteins Regulate the Cyclic AMP Pathway That Is Required for Development and Pathogenicity of the Phytopathogen Mycosphaerella graminicola{triangledown}

Rahim Mehrabi,1,2,{dagger} Sarrah Ben M'Barek,1,{dagger} Theo A. J. van der Lee,1 Cees Waalwijk,1 Pierre J. G. M. de Wit,2 and Gerrit H. J. Kema1*

Plant Research International B.V., Wageningen University and Research Centre (WUR), P.O. Box 16, 6700 AA Wageningen, The Netherlands,1 Laboratory of Phytopathology, WUR, Binnenhaven 5, 6709 PD Wageningen, The Netherlands2

Received 1 August 2008/ Accepted 17 April 2009

We identified and functionally characterized genes encoding three G{alpha} proteins and one Gβ 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{alpha}i and G{alpha}s families, respectively, whereas MgGPA2 is not related to either of these families. On potato dextrose agar (PDA) and in yeast glucose broth (YGB), MgGpa1 mutants produced significantly longer spores than those of the wild type (WT), and these 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 and showed a nested type of growth on PDA that was due to hampered filamentation, numerous cell fusions, and increased anastomosis. Intracellular cyclic AMP (cAMP) levels of MgGpb1 and MgGpa3 mutants were decreased, indicating that both genes positively regulate the cAMP pathway, which was confirmed because 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 concluded that the heterotrimeric G proteins encoded by MgGpa3 and MgGpb1 regulate the cAMP pathway that is required for development and pathogenicity in M. graminicola.

* Corresponding author. Mailing address: Plant Research International B.V., Wageningen University and Research Centre (WUR), P.O. Box 16, 6700 AA Wageningen, The Netherlands. Phone: 31.317.480632. Fax: 31.317.418094. E-mail: gert.kema{at}wur.nl

{triangledown} Published ahead of print on 1 May 2009.

{dagger} R.M. and S.B.M. contributed equally.

Eukaryotic Cell, July 2009, p. 1001-1013, Vol. 8, No. 7
1535-9778/09/$08.00+0     doi:10.1128/EC.00258-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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