Iron homeostasis alteration in transgenic tobacco overexpressing ferritin

Intracellular iron concentration requires tight control and is regulated both at the uptake and storage levels. Our knowledge of the role that the iron-storage protein ferritins play in plants is still very limited. Overexpression of this protein, either in the cytoplasm or the plastids of transgenic tobacco, was obtained by placing soybean ferritin cDNA cassettes under the control of the CAMV 35S promoter. The protein accumulated in 4- and 6-day-old seedlings and in leaves of 3-week-old plants but not in dry seeds or in 2-day-old seedlings, which is consistent with previous reports describing a post-transcriptional control of ferritin amounts during the germination process. Overaccumulated ferritin in leaves was correctly assembled as 24-mers. Transformants were more resistant to methylviologen toxicity, indicating that the transgenic ferritins were functional in vivo. Ferritin overaccumulation in transgenic tobacco leaves leads to an illegitimate iron sequestration. As a consequence, these transgenic plants behave as iron deficient and activate iron transport systems as revealed by an increase in root ferric reductase activity and in leaf iron content.