Over-expression of mitochondrial heat shock protein 70 suppresses programmed cell death in rice

In this study, we identified and functionally characterized the mitochondrial heat shock protein 70 (mtHsp70). Over-expression of mtHsp70 suppressed heat- and H₂O₂-induced programmed cell death (PCD) in rice protoplasts, as reflected by higher cell viability, decreased DNA laddering and chromatin condensation. Mitochondrial membrane potential (Δψ_m) after heat shock was destroyed gradually in protoplasts, but mtHsp70 over-expression showed higher Δψ_m relative to the vector control cells, and partially inhibited cytochrome c release from mitochondria to cytosol. Heat treatment also significantly increased reactive oxygen species (ROS) generation, a phenomenon not observed in protoplasts over-expressing mtHsp70. Together, these results suggest that mtHsp70 may suppress PCD in rice protoplasts by maintaining mitochondrial Δψ_m and inhibiting the amplification of ROS.