Evolution of C4 Photosynthesis: The Role of Low CO2 Environment

C4 photosynthesis has evolved many times independently from more than 60 different lineages.  Recruitment of existing components from C3 metabolism has been a recurrent theme during the evolution of C4 photosynthesis. In this talk, we show that many enzymes associated with the C4 metabolism was up-regulated under long-term low CO₂ conditions.  Transcriptomics study showed that the up-regulation might be related to the re-capturing of release of ammonia from enhanced photorespiration under long-term low CO₂ conditions. We discussed the possibility that historically long-term low CO₂ might have functioned not only as a screening agent, but also as a signal compound during the emergence of C4 photosynthesis.