Molecular cloning and characterization of a ferritin gene upregulated by cold stress in Chorispora bungeana

The ability of iron to accept and donate electrons makes it important for plant growth, but it can also damage plants when they are under environmental stress. Ferritin, a protein encoded by the gene Fer, catalyzes the oxidation of Fe(2+) and subsequent storage of Fe(3+) within the mineral core. Ferritin may reduce the adverse effects of iron on Chorispora bungeana Fisch. & C.A. May during the course of cold stress. C. bungeana is a rare alpine subnival plant species that is highly resistant to a freezing environment. We have isolated and characterized the ferritin cDNA (CbFer) from C. bungeana. It is 975 bp in length with an open reading frame of 260 amino acids, corresponding to a protein of predicted molecular mass of 29.17 kDa and an isoelectric point of 5.44. Amino acid analysis of the polypeptides indicated that CbFer codes for a ferritin subunit plus a chloroplast-targeting transit peptide. Reverse transcription polymerase chain reaction analysis confirmed that CbFer was a tissue-specific gene since the expression could only be detected in leaves. The gene expression patterns were investigated in relation to cold stress (4 degrees C and -4 degrees C) and to various exogenous signals, including excessive iron, hydrogen peroxide (H(2)O(2)), and nitrogen monoxidum (NO). The amount of CbFer mRNA increased in response to low temperatures and gene expression at -4 degrees C was both more distinct and quicker than that at 4 degrees C. Two exogenous signals, excessive iron and H(2)O(2), upregulated the expression of the CbFer gene, but NO had no effect. The CbFer gene may play an important role in response to cold stress, while the expression of the gene during stress may be influenced by major and minor factors such as iron and H(2)O(2), respectively.