Abstract :
[en] Tong Lian. (2022). Investigating the genetic basis and regulatory mechanism of folate metabolism in maize (Zea mays) (PhD Dissertation in English). Gembloux, Belgium, Gembloux Agro-Bio Tech, University of Liège, 132 p., 12 tables, 29 figures.
Abstract — Folates, one group of the essential B vitamins, play a crucial role in DNA biosynthesis, amino acid metabolism, and DNA methylation during the development and growth of organisms. Daily diet is the major source of folates for human beings. The low-level intake of folates may cause increase of the risk of number of serious diseases such as cancers and neural tube defects. The folate contents in crop plants, especially cereals, are quite low. Therefore, it’s necessary to improve the folate accumulation in crops, an approach called biofortification, to alleviate the folate deficiency problem worldwide. To this end, it’s imperative to understand the genetic basis and regulatory mechanism of folate metabolism in crops. Here we have designed two projects to identify the key metabolic pathways or genes that may contribute to folate accumulation in maize kernel.
(1) Comparative transcriptome analysis reveals mechanisms of folate accumulation in maize grains
Previously, the complexity of folate accumulation in the early stages of maize kernel development was reported, but the mechanisms remain unclear. In this study, two maize inbred lines, DAN3130 and JI63, with different folate accumulation patterns and levels in mature kernels were used to investigate the transcriptional regulation of folate metabolism by comparative transcriptome analysis. It was demonstrated that the folate accumulation during DAP 24 to kernel maturity was controlled by the circumjacent pathways of folate biosynthesis, such as pyruvate metabolism, glutamate metabolism, and serine/glycine metabolism. In addition, the differences in folate accumulation between these two inbred lines were found to be related to those genes involved in folate metabolism, including those in pteridine branch, para-aminobenzoate branch, serine/tetrahydrofolate (THF)/5-methyltetrahydrofolate cycle, and conversion of THF monoglutamate to THF polyglutamate. Those observations provided insight into the mechanisms underlying folate metabolism during maize kernel formation, thus being helpful for folate biofortification research in maize.
(2) Genetic mapping of folate QTLs using a segregated population in maize (Zea mays L.)
To increase folate accumulation in edible parts of crops is of great importance for human health. Molecular breeding is a feasible and efficient strategy for folate biofortification, but somewhat constrained by shortage of the knowledge on folate metabolism at molecular level. In this study, we reported the genetic mapping of the quantitative trait loci (QTLs) linking with folate accumulation levels using a segregated population crossed by two maize lines, one high in folates (GEMS31) and the other low in folates (DAN3130). As a result, two QTLs on chromosome 5 were obtained by association of whole-exome sequencing with kernel folate profiling. These QTLs were confirmed by bulk segregant analysis using pooled DNA in F6 and kernel folate profiling in F7, with an overlap with the QTLs identified in another segregated population. One candidate gene, named ZmCTM, was identified as a gene encoding a folate-binding protein that played an important role in folate metabolism in maize. Loss of ZmCTM function enhanced 5-methyl-tetrahydrofolate accumulation by three folds. We concluded that ZmCTM may participate in folate metabolism by converting 5-methyl-tetrahydrofolate to other folate derivatives in maize.
