| In recent years small G proteins have become an intensively studied group of regulatory GTP hydrolases involved in cell signaling of eukaryotes. Small GTPases form an independent superfamily. This superfamily contains proteins that control a vast number of important processes and possess a common, structurally preserved GTP-binding domain. The small GTPase superfamily can be devided into eight different families: Arf, Ran, Rab, Rho, Ras, Sar1, Mitochondrial Rho, Roc small GTPases domain. Rho GTPases control cytoskeleton reorganization. In fungi, Rho1 is shown to be involved in the regulation of cell morphogenesis, Rho2, Rho3 and Rho4 are implicated in the regulation of cell differentiation and polarity growth. There exists sophisticated Rho GTPase signal pathways in the fungus, and they may regulate each other among these Rho GTPases.In this study, the amino acid sequences of Rho2 homolog in Magnaporthe oryzae was analyzed by bioinformatics and a detailed analysis of physicochemical properties, domains, homologs, motifs, enzymatic digestion sites, phylogenetic relationships are presented. Further functional analysis of Rho2 in Magnaporthe oryzae was analyzed by gene knock-out techniques. Deletion of MgRho2 had no effects on conidiation and colony growth. And the septation of conidia and hyphal were normal. But appressorium formation of MgRho2 deletion mutants were relatively delayed in spite of returning to the level of wild-type strain after further incubation. Furthermore, MgRho2 deletion mutant could penetrate onion as wild-type strain. But the rate of penetration of reduced which corresponded to delay of appressorium formation. When inoculating on barley leaves and rice leaves, there was no difference on pathogenicity between the deletion mutant and wild-type strain. These results suggest that Rho2 is not as important as other Rho members in the fungal pathogenesis, but it may regulate appressorium development of the fungus, the mechanism under which needs to further study. |
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