Knockdown of GDCH gene reveals reactive oxygen species-induced leaf senescence in rice

Glycine decarboxylase complex (GDC) is a multi-protein complex, comprising P-, H-, T-and L-protein subunits, which plays a major role in photorespiration in plants. While structural analysis has demonstrated that the H subunit of GDC (GDCH) plays a pivotal role in GDC, research on the role of GDCH in biological processes in plants is seldom reported. Here, the function of GDCH, stresses resulting from GDCH-knockdown and the interactions of these stresses with other cellular processes were studied in rice plants. Under high CO2, the OsGDCH RNA interference (OsGDCH-RNAi) plants grew normally, but under ambient CO2, severely suppressed OsGDCH-RNAi plants (SSPs) were non-viable, which displayed a photorespiration-deficient phenotype. Under ambient CO2, chlorophyll loss, protein degradation, lipid peroxidation and photosynthesis decline occurred in SSPs. Electron microscopy studies showed that chloroplast breakdown and autophagy took place in these plants. Reactive oxygen species (ROS), including O-2(-) and H2O2, accumulated and the antioxidant enzyme activities decreased in the leaves of SSPs under ambient CO2. The expression of transcription factors and senescence-associated genes (SAGs), which was up-regulated in SSPs after transfer to ambient CO2, was enhanced in wild-type plants treated with H2O2. Evidences demonstrate ROS induce senescence in SSPs, and transcription factors OsWRKY72 may mediate the ROS-induced senescence.