Down-regulation of rice serpin gene OsSRP-LRS exaggerates stress-induced cell death

Serine protease inhibitors (serpins) and their cognate proteases control diverse physiological processes, including program cell death and immune response, in insects and mammals. Arabidopsis AtSerpin1 inhibits pro-cell-death proteases and protects cells from excessive cell death induced by pathogens. The rice genome contains at least 14 serpin coding genes, but a biological role is not known for any of them. We show here that expression of rice serpin1 (OsSRP-LRS; the closest homolog of AtSerpin1 in rice) is induced by necrotrophic fungal pathogen Rhizoctonia solani inoculation, UV and salt treatment. The transgenic RNAi lines having reduced expression of OsSRP-LRS are morphologically unaffected under the stress-free condition, but show exaggerated cell death upon pathogen, UV or salt treatment. Our results suggest that OsSRP-LRS negatively regulates stress-induced cell death in rice.