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A Rho3 Homolog Is Essential for Appressorium Development and Pathogenicity of Magnaporthe grisea

Wu Zheng ,^, Jisheng Chen, Wende Liu, Shiqin Zheng, Jie Zhou, Guodong Lu,^* and Zonghua Wang^*

The Key Laboratory of Biopesticide and Chemistry Biology, Ministry of Education, Fujian Agriculture and Forestry University, Fuzhou 350002, People's Republic of China

Received 2 April 2007/ Accepted 1 October 2007

The small GTPase Rho3 is conserved in fungi and plays a key role in the control of cell polarity and exocytosis in yeast. In this report, we show that a Rho3 homolog, MgRho3, is dispensable for polarized hyphal growth in the rice blast fungus Magnaporthe grisea. However, MgRho3 is required for plant infection. Appressoria formed by the Mgrho3 deletion mutants are morphologically abnormal and defective in plant penetration. Conidia of the Mgrho3 deletion mutants are narrower than those of the wild-type strain and delayed in germination. Transformants expressing a dominant negative Mgrho3 allele exhibit similar phenotypes as the Mgrho3 deletion mutant, while transformants expressing a constitutively active allele of MgRho3 can produce normal conidia but remain defective in appressorium formation and plant infection. In contrast, overexpression of wild-type MgRho3 increases the infectivity of M. grisea. Our results reveal a new role for the conserved Rho3 as a critical regulator of developmental processes and pathogenicity of M. grisea.

Published ahead of print on 12 October 2007.

W.Z. and J.C. contributed equally to this work.

Present address: Fuzhou Criminal Science & Technology Institute, Fuzhou 350003, People's Republic of China.