Genome-Wide Identification and Analysis of Biotic and Abiotic Stress Regulation of C 4 Photosynthetic Pathway Genes in Rice

Photosynthetic fixation of CO2 is more efficient in C4 than in C3 plants. Rice is a C3 plant and a potential target for genetic engineering of the C4 pathway. It is known that genes encoding C4 enzymes are present in C3 plants. However, no systematic analysis has been conducted to determine if these C4 gene family members are expressed in diverse rice genotypes. In this study, we identified 15 genes belonging to the five C4 gene families in rice genome through BLAST search using known maize C4 photosynthetic pathway genes. Phylogenetic relationship of rice C4 photosynthetic pathway genes and their isoforms with other grass genomes (Brachypodium, maize, Sorghum and Setaria), showed that these genes were highly conserved across grass genomes. Spatiotemporal, hormone, and abiotic stress specific expression pattern of the identified genes revealed constitutive as well as inductive responses of the C4 photosynthetic pathway in different tissues and developmental stages of rice. Expression levels of C4 specific gene family members in flag leaf during tillering stage were quantitatively analyzed in five rice genotypes covering three species, viz. Oryza sativa, ssp. japonica (cv. Nipponbare), Oryza sativa, ssp. indica (cv IR64, Swarna), and two wild species Oryza barthii and Oryza australiensis. The results showed that all the identified genes expressed in rice and exhibited differential expression pattern during different growth stages, and in response to biotic and abiotic stress conditions and hormone treatments. Our study concludes that C4 photosynthetic pathway genes present in rice play a crucial role in stress regulation and might act as targets for C4 pathway engineering via CRISPR-mediated breeding.