Regulatory preconditioning for the evolution of C₄photosynthesis revealed by low CO₂treatment of Arabidopsis thaliana

Abstract Low CO 2 condition was considered a preconditioning or selection pressure for C 4 evolution. However, it remains elucidated how low CO 2 condition contribute to the evolutionary assembly of the C 4 pathway. We conducted a systematic transcriptomics and metabolomics analysis under short-term low CO 2 condition and found that Arabidopsis grown under this condition showed increased expression of most genes encoding C 4 - related enzymes and transporters. Low CO 2 condition increased NH 4 + content in leaves; as expected, photorespiratory and ammonia refixing pathways were enhanced. Furthermore, we found that compared to low CO 2 condition, in vitro treatment with NH 4 + induced a similar pattern of changes in C 4 related genes and genes involved in ammonia refixation. This supports that increased expression of C 4 genes induced by low CO 2 condition can supply carbon skeleton for ammonia recycling. This study provides new insight into the regulatory preconditioning which may have facilitated the evolution of C 4 photosynthesis under low atmospheric CO 2 environments.