GTP cyclohydrolase 1 expression and folate accumulation in the developing wheat seed

Abstract

Folates are essential cofactors required by most living organisms yet only plants and microorganisms have retained the ability of de novo synthesis. Human deficiencies remain prevalent due to inadequate dietary intake. Cereals are the most widely consumed plant product yet fail to supply sufficient levels of folates, however an active folate pathway in seeds identifies cereals as a potential target for biofortification. GTP cyclohydrolase 1 mRNAs were isolated from developing wheat seed tissues, leaves and roots suggesting de novo folate synthesis is occurring throughout the wheat plant. A homologous gene was identified in the rice genome sequence revealing both wheat and rice GCH1 transcripts have conserved features identified in other plant GCH1 genes. Wheat seed transcripts produced functional recombinant proteins which catalysed the formation of dihydroneopterin triphosphate from GTP. A differential expression profile of GCH1 transcripts occurred throughout seed development whereas folate accumulation decreased. Interestingly, the mature seed has retained GCH1 activity only in the embryo and maternal layers which explains the apparent partitioning of folate accumulation in the mature seed. The wheat seed has a continually active folate biosynthetic pathway through development and by inference the capacity to produce folate continues as long as the seed remains viable.