Ferritins and iron storage in plants.

Iron is essential for both plant productivity and nutritional quality. Improving plant iron content was attempted through genetic engineering of plants overexpressing ferritins. However, both the roles of these proteins in the plant physiology, and the mechanisms involved in the regulation of their expression are largely unknown. Although the structure of ferritins is highly conserved between plants and animals, their cellular localization differ. Furthermore, regulation of ferritin gene expression in response to iron excess occurs at the transcriptional level in plants, in contrast to animals which regulate ferritin expression at the translational level. In this review, our knowledge of the specific features of plant ferritins is presented, at the level of their (i) structure/function relationships, (ii) cellular localization, and (iii) synthesis regulation during development and in response to various environmental cues. A special emphasis is given to their function in plant physiology, in particular concerning their respective roles in iron storage and in protection against oxidative stress. Indeed, the use of reverse genetics in Arabidopsis recently enabled to produce various knock-out ferritin mutants, revealing strong links between these proteins and protection against oxidative stress. In contrast, their putative iron storage function to furnish iron during various development processes is unlikely to be essential. Ferritins, by buffering iron, exert a fine tuning of the quantity of metal required for metabolic purposes, and help plants to cope with adverse situations, the deleterious effects of which would be amplified if no system had evolved to take care of free reactive iron.