A new family of ferritin genes from lupinus luteus-comparative analysis of plant ferritins, their gene structure, and evolution

Abstract

Ferritins are one of the most important elements of cellular machinery involved in iron management. Despite extensive studies conducted during the last decade, many factors regulating the expression of ferritin genes in plants remain unknown. To broaden our knowledge about the mechanisms controlling ferritin production in plant cells, we have identified and characterized a new family of ferritin genes (from yellow lupine). We have also inventoried all available plant ferritins and their genes and subjected them to a complex bioinformatic analysis. It showed that the conservative structure of ferritin genes was established much earlier than it was thought before. The first introns in ferritin genes appeared already in green algae. The number and location of introns have been finally established in mosses, over 400 million years ago, and are strictly preserved in all plants from bryophytes to dicots. Comparison of ferritin gene promoters revealed that the 14-bp-long iron-dependent regulatory sequence (IDRS), identified earlier in Arabidopsis and maize, is characteristic for all higher plants. Moreover, we found that a highly conserved IDRS can be extended (extIDRS) up to 22 bp. Phylogenetic analysis of plant ferritins showed that polypeptides of the eudicot clade can be divided into two subclasses (eudicot-1 and eudicot-2). Interestingly, we found that genes encoding proteins classified as eudicot-1 and eudicot-2 are equipped with class-specific promoters. This suggests that eudicot ferritins are structurally and perhaps functionally diverse. Based on the above observations, we were able to identify conservative elements (ELEM1-6) other than extIDRS within plant ferritin gene promoters. We also found E-boxes and iron-responsive sequence elements FeRE1 and 2, characteristically distributed within ferritin promoters. Because most of the identified conserved sequences are located within or in close proximity of extIDRS, we named this fragment of the plant ferritin gene promoter the regulatory element rich region.