Functional genes found for three different plant ferritin subunits in the legume, Vigna unguiculata.

The iron storage protein, ferritin, in plants can occur in multiple molecular forms that, until now, were proposed to be derived from degradation of a single mature polypeptide subunit (2,7,17), which is assembled into the holoprotein and functions in plastids. We have carried out some definitive experiments with the diploid legume, Vigna unguiculata (cowpeas), which show that there are functioning genes for three different ferritin subunits in the developing leaves. Unique segments of mRNAs which code for subunits with substantially different mature sequences were detected by PCR. Separate genes for each subunit were found by showing that each gene contained a unique intron. Thus, multiple molecular forms of ferritin can arise through differential expression of a family of genes in plants.