Occurrence and expression of members of the ferritin gene family in cowpeas

Ferritin gene expression has been demonstrated in a variety of plants inclu ding maize, Arabidopsis, cowpeas, soybeans, beans and peas. Most available evidence shows that the mature protein is located in plastids and its produ ction is under gene transcriptional control. In maize, two different ferrit in genes have been identified; they were found to express protein under dif ferent physiological conditions. Only single gene products have been found until now in the other plants, with the exception of cowpeas (Vigna unguicu lata). Our previous work with cowpeas [Wicks and Entsch (1993) Biochem. Bio phys. Res. Commun. 192, 813-819] showed the existence of a family of at lea st three ferritin genes, each coding for a protein subunit with a unique am ino acid sequence. Here we report the discovery of a fourth active gene in cowpeas and present the full cDNA sequences for two of the four known membe rs of the cowpea gene family. We also provide preliminary evidence for a fa mily of ferritin genes in soybeans (Glycine max) related to that in cowpeas . We conclude that a family of genes is probably present in all higher plan ts. We have used quantitative reverse transcriptase-mediated PCR to show th at each of the four members of the cowpea ferritin gene family expresses mR NA in leaves and roots under normal growth with a complete nutrient supply. The results clearly show a marked differential pattern of mRNA levels form ed during development from the four genes. We conclude that the composition of plant ferritin molecules from plant leaf extracts is probably a complex mixture of subunits, which might be different in roots and in leaves.