Study on the role of OsCTPS in rice seed development

초록

Cytidine triphosphate (CTP) plays an essential role in the biosynthesis of DNA, RNA and phospholipids. CTP synthase (CTPS) is the rate-limiting enzyme in cytosine nucleotide biosynthesis. Mutations in OsCTPS1 resulted in an endospermless phenotype and an enlarged embryo. Conversely, OsCTPS1-overexpressing (OX) plants showed increased seed size and weight. The rice genome contains a total of six OsCTPS genes, including OsCTPS1. To elucidate the functions of the remaining OsCTPS genes expressed during seed development, mutant individuals of these genes were generated using the CRISPR/Cas9 method. Null mutants of OsCTPS2, OsCTPS5, and OsCTPS6 showed defects in seed development, whereas OsCTPS5 OX plants increased seed size and weight, similar to OsCTPS1 OX plants. Interestingly, OsCTPS2 OX or OsCTPS6 OX plants showed reduced seed weight and size. Since we found no significant difference and no specificity in the interaction between each of the OsCTPS proteins in the co-immunoprecipitation (co-IP) experiments, we speculated that this was probably due to differences in the enzymatic activity of each of these proteins for CTP synthesis. OsCTPS1 includes a CTP synthase domain and a glutamine amide transfer domain. To understand the function of these domains, we generated deletion mutants at various sites in both domains. We are observing the phenotype of the seeds to confirm the phenotype of the mutants we created. In addition, comparative amino acid sequence analysis revealed that OsCTPS2 and OsCTPS6, which negatively affected seed development when overexpressed, did not have a conserved 36th serine residue, which is known to play an important role in the phosphorylation of CTPS proteins. We are still carrying out further studies to determine whether this residue may play a role in CTP synthase activity to control seed development.