Genome-wide Identification And Spatio-temporal Analysis Of Folate Metabolism-related Genes In Maize

Folates are major water-soluble B-vitamins that play an important role as one carbon donors and acceptors, which involved in DNA biosynthesis, amino acid metabolism and methylation in organisms. Humans cannot synthesize folate de novo, and folate deficiency becomes a global public health problem. Hence, in order to enhance the stable folate accumulation in the edible parts in crops to alleviate this problem, it is necessary to further increase our understanding in the regulatory mechanism of folate metabolism. In this study, maize was selected as the subject, and a systemic analysis of folate metabolism-related genes in maize were performed. A total of 36 candidate genes corresponding to 16 folate metabolism-related enzymes which contain highly conserved domains in maize were identified by sequence alignment and conservation analysis. Phylogenetic trees results indicated that folate metabolism-related proteins in maize are conserved and have a close relationship with those in sorghum and millet. The folates contents in mature seeds were measured in more than 200 maize inbred lines across the years by using liquid chromatography-tandem mass spectroscopy. And the folates contents in inbred lines GEMS31 was always at least 11.9-folds higher than those detected in the inbred lines Ji63. Thus various organs of these two representative maize inbred lines were selected to analyze the folates contents, transcriptional profiling and amino acid sequences during maize development. The main results are listed as follows:1.The results of folates contents in maize various organs(root, stem, leaf, cob, and kernel) indicated that 5-methyltetrahydrofolate(5-M-THF) was the major form of folates derivatives in stems, cobs and kernels at the early stages, and 5-formyltetrahydrofolate(5-F-THF) was in mature seeds. The major folate derivatives in leaves and roots were different between these two inbred lines. During days after sowing 30, total folates contents decreased obviously in roots, while increased gradually in leaves. As observed in mature kernels, the 5-F-THF levels and total folates contents in GEMS31 were always higher than those in Ji63 in every organs detected.2. Real-time PCR results indicated that most of the genes involved in folate metabolism exhibited different transcriptional patterns between these two lines in roots, stems, leaves and cobs,but no obvious regularity was found. And the transcript abundance of most folate metabolism-related genes in leaves higher than that in roots on day after sowing 30. Meanwhile, most of the genes involved in folate metabolism exhibited similar transcriptional patterns between these two lines in immature kernels, with the highest transcript abundance was detected on day after pollination(DAP) 6 and the transcript abundance decreased on DAP 12 and DAP 18.3. No differences were observed between the coding sequences of folate metabolism-related genes in these two inbred lines.Taken together, these findings suggest that folate metabolism is conserved between maize and other species. Metabolite profiling demonstrates that 5-M-THF is the dominant folate derivative in early developing seeds, cobs and stems, and 5-F-THF is the major storage form in mature seeds. These two folate derivatives play different roles in each organ during maize development. Genes involved in folate metabolism are actively expressed at the early stages of kernel development. Although these two maize inbred lines perform a significant difference in folates contents in mature seeds, the transcriptional profillings and translation of the genes involved in folate metabolism is the same. And no obvious relationship between the transcriptional profillings and the folates contents in mature seeds was observed. This study indicated that folate metabolism is complicated during kernel development in maize.