A specific protective mechanism against chloroplast photo-reactive oxygen species in phosphate-starved rice plants [ChIP-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. Chromatin immunoprecipitation DNA-sequencing (ChIP-seq) for GLK1 and GLK2 in rice leaves under control or Pi-starved conditions (3 d after transferring to non-Pi medium).