Abstract:  Rho protein family， a core member of the Ras superfamily in eukaryotes， contains the highly conserved GTPases domain. Three small Rho proteins were isolated from arbuscular mycorrhizal fungi Rhizophagus irregularis DAOM197198 through homolog research and RACE PCR strategies. Using real time qPCR method， the transcription profiles of the three genes during presymbiotic and symbiotic stages were analyzed. To further study the roles of RiRho1 and RiCDC42 genes, complementary experiments were carried out in yeast Ts mutant and fungal pathogen Magnaporthe oryzae ΔMgCDC42. The results indicated that RiRho1， RiRac1 and RiCDC42 proteins were highly similar to Rho proteins in M. oryzae. RiRho1 was highly induced in germination spores， whereas its transcripts were lower during the AM symbiosis. In contrast， expressions of RiRac1 and RiCDC42 were significantly higher at symbiotic stages than that in presymbiotic stage. RiRho and RiCDC42 can partially rescue the yeast mutant. Furthermore， the RiCDC42 was able to rescue the phenotype of the M. oryzae CDC42 mutant. However， the mutant expressing RiCDC42 gene did not generate the melanin. The roles RiRac1 and RiCDC42 played were further confirmed by host induced gene silence （HIGS）. Taken as a whole， the above data and results suggested that the Rho protein may play important roles during the arbuscular mycorrhizal symbiosis.

Key words: Rho family protein, AM symbiosis, Rhizophagus irregularis, HIGS