Identification of Photosynthesis-Associated C(4) Candidate Genes through Comparative Leaf Gradient Transcriptome in Multiple Lineages of C(3) and C(4) Species

Leaves of C(4) crops usually have higher radiation, water and nitrogen use efficiencies compared to the C(3) species. Engineering C(4) traits into C(3) crops has been proposed as one of the most promising ways to repeal the biomass yield ceiling. To better understand the function of C(4) photosynthesis, and to identify candidate genes that are associated with the C(4) pathways, a comparative transcription network analysis was conducted on leaf developmental gradients of three C(4) species including maize, green foxtail and sorghum and one C(3) species, rice. By combining the methods of gene co-expression and differentially co-expression networks, we identified a total of 128 C(4) specific genes. Besides the classic C(4) shuttle genes, a new set of genes associated with light reaction, starch and sucrose metabolism, metabolites transportation, as well as transcription regulation, were identified as involved in C(4) photosynthesis. These findings will provide important insights into the differential gene regulation between C(3) and C(4) species, and a good genetic resource for establishing C(4) pathways in C(3) crops.