Ferric reduction oxidase 2 gene from Pyrus betulifolia is regulated by iron deficiency and auxin

Pyrus betulifolia Bunge belongs to the woody plant family and is an ideal model for studying molecular strategies of iron acquisition and metabolism in strategy I plants. Using polymerase chain reaction amplification technology, a gene encoding a putative ferric chelate reductase (FCR) protein was isolated from P. betulifolia and designated as PbFRO2. This gene was 2166 bp in length with an open reading frame encoding a protein of 721 amino acids. A hidden Markov model for topology prediction of PbFRO2 suggested that there were 10 transmembrane regions (I–X) connected by nine loops. Phylogenetic analyses demonstrated that PbFRO2 had the highest homology with Malus xiaojinensis Cheng & Jiang. Iron starvation induced significant increase in root FCR activity and PbFRO2 expression. The split-root experiment demonstrated that Fe limitation in one portion of the root system triggered significant up-regulation of the PbFRO2 expression in the Fe-sufficient part, suggesting that the PbFRO2 expression was induced by systemic signals. Furthermore, the addition of α-naphthaleneacetic acid was found to strengthen the Fe deficiency-caused up-regulation of the PbFRO2 expression in the roots. By contrast, 1-naphthylphthalamic acid application blocked up-regulation of the PbFRO2 expression. The results indicated that Fe deficiency-induced alterations of the PbFRO2 expression were mediated by auxin.