Knockdown of OsPAO and OsRCCR1 cause different plant death phenotypes in rice

Pheophorbide a oxygenase (PAO) and red chlorophyll catabolite reductase (RCCR) catalyze key steps in chlorophyll degradation by opening the porphyrin macrocycle of pheophorbide a and forming the primary non-photoreactive fluorescent chlorophyll catabolite. These genes strongly participate in senescence and reportedly involved in plants' responses to physical wounding and pathogens. In this report, a single PAO gene (OsPAO) and two RCCR genes (OsRCCR1 and OsRCCR2) have been isolated from rice. Expression analysis by semi-quantitative PCR or quantitative real-time PCR showed that OsRCCR1 transcripts were much more abundant than OsRCCR2, and all of these genes were upregulated during senescence and following wound treatment. RNA interference knockdown of OsPAO led to pheophorbide a accumulation in leaves (especially dark-induced senescent leaves) and leaf death from regeneration stage onwards, even transgenic plants inviability after transplantation. While, knockdown of OsRCCR1 resulted in lesion-mimic spots generation in older leaves which died off early in the transgenic plants. These results suggest that OsPAO and OsRCCR1 play key roles in senescence and are involved in wound responses.