Cloning and functional analysis of an endo-PG-encoding gene Rrspg1 of Rhizoctonia solani, the causal agent of rice sheath blight

By assembling the sequences of the cDNA obtained from RT-PCR, 5'-RACE and 3'-RACE, a full-length sequence of the endo-polygalacturonase (endo-PG) -encoding gene, Rrspg1, from the rice sheath blight fungus Rhizoctonia solani, was obtained. The alignment of cDNA and genomic DNA sequences indicated that there were three introns in the sequence of Rrspg1. Differences in six nucleotides and four amino acids were found between isolates originating from rice and maize. To verify the function of Rrspg1, the RNAi vector pSilent-PG-2 was constructed and used to transform the rice wild-type (WT) isolate GD-118 of R. solani. Assays of PG activity between transformants and isolate GD-118 showed that 10 transformants had significantly lower PG activity compared with WT isolate. Pathogenicity tests indicated that the virulence of six transformants was weaker than that of WT isolate, which verified that Rrspg1 plays an important role in the pathogenesis of R. solani to rice plants.