Folates in plants:: biosynthesis, distribution, and enhancement

Folates are crucial intermediates for a set of reactions that involve the transfer of single-carbon units (C1 metabolism). They are directly involved in the synthesis of nucleic acids, methionine, pantothenate, glycine and serine, and indirectly, through S-adenosyl methionine, in all methylation reactions. Humans cannot synthesize folates de novo. In these organisms, folate deficiency has severe effects on health and affects large population groups around the world. Because plants are the main source of dietary folates, there are great concerns to select plant food having high concentrations of folates or to engineer their folate metabolism to increase the initial amount. All these attempts rely on what we know about the metabolism of folates. During these last 10 years, the complex pathway leading to the synthesis of folates has been deciphered. Our knowledge about folate synthesis and distribution during plant growth and development also increased substantially. However, important aspects of folate metabolism remain unclear, such as catabolism, transport and regulation of the homeostasis. The aim of this review was to summarize our recent findings, to describe the few attempts reported in the literature to engineer folate level in plants, and to discuss potential strategies that could be used for enhancement.