Folate synthesis and compartmentation in higher plants

Folate is a crucial intermediate for one-carbon metabolism. In higher plants, folate derivatives are found in the cytosol, mitochondria and, to a lesser extent, chloroplasts together with the enzymes serine hydroxymethyltransferase and methylenetetrahydrofolate reductase/cyclohydrolase required for the generation and interconversion of the one-carbon substituted folates. The sources of these one-carbon units include formate, glycine and serine. A defining feature of plant folate metabolism is that the synthesis of the tetrahydrofolate from 6-hydroxymethyldihydropterin and p-aminobenzoic acid, and its subsequent conversion to physiologically active polyglutamyl derivatives appears to be confined to the mitochondria. This leads to important questions regarding the intracellular transport of folate and its precursors, but for the moment the mechanisms involved are unknown.