Functional analysis of polygalacturonase gene RsPG2 from Rhizoctonia solani, the pathogen of rice sheath blight

Rice sheath blight, which is caused by Rhizoctonia solani, is a devastating disease in many areas of the world where rice is cultivated. The role of polygalacturonase (PG) in the infection process of R. solani was investigated in the present study by cloning and investigating the function of a new PG-encoding gene, which was designated RsPG2. Bioinformatics showed that RsPG2 consisted of a 1,633 bp open reading frame (ORF) with six introns; the deduced protein contained 436 amino acids with a predicted mass of 45.88 kDa after cleavage of the predicted 17-amino acid signal sequence. Culture supernatants obtained from Pichia pastoris producing recombinant RsPG2 degraded polygalacturonic acid in vitro, thus confirming that RsPG2 encodes a PG gene. Purified recombinant RsPG2 also degraded rice tissue and elicited obvious necrotic symptoms 48 h after inoculation. Real-time qRT-PCR indicated that the expression of RsPG2 was strongly induced during the infection of rice by R. solani. These data unequivocally demonstrate that RsPG2 plays an important role in R. solani infection and provide further insights for elucidating the function of pg genes in the virulence of R. solani.