Genome-wide identification and comparative analyses of key genes involved in C<subscript>4</subscript> photosynthesis in five main gramineous crops.

Compared to C 3 species, C 4 plants showed higher photosynthetic capacity as well as water and nitrogen use efficiency due to the presence of the C 4 photosynthetic pathway. Previous studies have shown that all genes required for the C 4 photosynthetic pathway exist in the genomes of C 3 species and are expressed. In this study, the genes encoding six key C 4 photosynthetic pathway enzymes (β-CA, PEPC, ME, MDH, RbcS, and PPDK) in the genomes of five important gramineous crops (C 4 : maize, foxtail millet, and sorghum; C 3 : rice and wheat) were systematically identified and compared. Based on sequence characteristics and evolutionary relationships, their C 4 functional gene copies were distinguished from non-photosynthetic functional gene copies. Furthermore, multiple sequence alignment revealed important sites affecting the activities of PEPC and RbcS between the C 3 and C 4 species. Comparisons of expression characteristics confirmed that the expression patterns of nonphotosynthetic gene copies were relatively conserved among species, while C 4 gene copies in C 4 species acquired new tissue expression patterns during evolution. Additionally, multiple sequence features that may affect C 4 gene expression and subcellular localization were found in the coding and promoter regions. Our work emphasized the diversity of the evolution of different genes in the C 4 photosynthetic pathway and confirmed that the specific high expression in the leaf and appropriate intracellular distribution were the keys to the evolution of C 4 photosynthesis. The results of this study will help determine the evolutionary mechanism of the C 4 photosynthetic pathway in Gramineae and provide references for the transformation of C 4 photosynthetic pathways in wheat, rice, and other major C 3 cereal crops. [ABSTRACT FROM AUTHOR]

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