C gene induction during de-etiolation evolved through changes in cis to allow integration with ancestral C gene regulatory networks.

C photosynthesis has evolved by repurposing enzymes found in C plants. Compared with the ancestral C state, accumulation of C cycle proteins is enhanced. We used de-etiolation of C and C to understand this process. C gene expression and chloroplast biogenesis in were tightly coordinated. Although C and C photosynthesis genes showed similar induction patterns, in , C genes were more strongly induced than orthologs from . In vivo binding of TGA and homeodomain as well as light-responsive elements such as G- and I-box motifs were associated with the rapid increase in transcripts of C genes. Deletion analysis confirmed that regions containing G- and I-boxes were necessary for high expression. The data support a model in which accumulation of transcripts derived from C photosynthesis genes in C leaves is enhanced because modifications in cis allowed integration into ancestral transcriptional networks.