Cloning and function analysis of polygalacturonase gene RsPG5 in Rhizoctonia solani, the pathogen of rice sheath blight

Abstract:

[Background] Sheath blight, caused by Rhizoctonia solani, is one of the major devastated rice diseases in the world, while little is known about the pathogenic mechanism of the pathogen. [Objective] To identify more virulence genes from R. solani and provide a theoretical basis for the control of sheath blight. [Methods] The full-length sequence of RsPG5 was obtained by 3'-RACE, and the structure and biological properties of the deduced protein were predicted by ExPASy online. The pathogenic function of RsPG5 was then determined. [Results] RsPG5 harbored seven exons and six introns, with the coding region of 1 263 bp, which encoded 420 amino acid residues. RsPG5, one member of the glucoside hydrolase family 28, contained a signal peptide of 15 residues and NTD, DD, GHG and RF(I)K domains conserved in the polygalacturonases from fungi. The secondary structure of the deduced protein contained 4 disulfide bonds, α-helix, β-sheet, and random coil, which arranged according to right-handed helix and formed a cleft that was responsible for the enzyme activity. RsPG5 was a stable, water-soluble, exocrine protein localized in cell wall, vacuole, and mitochondria. The eukaryotic expression products of RsPG5 had the polygalacturonase activity to hydrolyze pectin and destroy the sheath cells of rice. Distinct brown necrotic spots appeared 72 h after the expression products were inoculated in the rice sheathes by a needle. The expression level of RsPG5 was up-regulated in the infection course of R. solani. [Conclusion] RsPG5 is a typical polygalacturonase and a major pathogenic factor of R. solani.