A specific protective mechanism against chloroplast photo-reactive oxygen species in phosphate-starved rice plants [RNA-seq]

Phosphorus (Pi) starvation prevents a good match between light energy absorption and photosynthetic carbon metabolism. Photosynthetic electron-transport chain switches to use molecular oxygen as an electron carrier, generating photo-reactive oxygen species (photo-ROS) in chloroplast. In rice (Oryza sativa), DEEP GREEN PANICLE1 (DGP1) is robustly up-regulated in response to Pi-deficiency stress. DGP1 decreases the DNA-binding activities of the photosynthetic activators GLK1/2 on the genes involved in chlorophyll biosynthesis, light harvesting and electron transport. This Pi-starvation-induced mechanism dampens electron transport rates (ETRI and ETRII) and alleviates the electron-excessive stress in mesophyll cells. Meanwhile, DGP1 hijacks glycolytic enzymes GAPC1/2/3, redirecting glucose metabolism toward pentose phosphate pathway with superfluous NADPH production. Phenotypically, light irradiation induces O2– accumulation in Pi-starved WT leaves, but was observably accelerated in dgp1 mutant and impaired in GAPCsRNAi line and glk1glk2 double mutant. Interestingly, overexpression of DGP1 in rice caused hyposensitivity to the ROS-inducers (catechin and methyl viologen) and dgp1 mutant shows a similar inhibitory growth with the WT plants. We conclude that DGP1 gene serves as a specific antagonizer against Pi-starvation-induced photo-ROS, which integrates light-absorbing and anti-oxidative systems by orchestrating transcriptional and metabolic regulations, respectively. We examined the transcriptional data in leaves of glk1glk2 and dgp1 mutants with their WT (DJ) plants under normal growth or low-Pi stress (10 µM KH2PO4).