Characterization and Expression Analysis of PbCS1 Gene Regulated by Iron Deficiency and Involved in Response to Auxin in Pyrus betulifolia

Iron (Fe) is an essential micronutrient required by all fruit trees. To elucidate the regulatory mechanism of auxin to the long-distance transport of Fe, a gene encoding a putative CS protein was isolated from Pyrus betulifolia. This gene was designated as PbCS1 containing 1 422 bp in length with an open reading frame encoding a protein of 473 amino acids with a predicted molecular mass of 52.69 ku and a theoretical isoelectric point of 6.91. The deduced PbCS1 protein contained a conserved CS domain and WPNVDAHS sequence existing in the PWPN-box. Based on its conserved domain and phylogenetic status, the PbCS1 should be grouped into type-Ⅰ subfamily of plant CS. Quantitative real-time PCR results indicated that the PbCS1 expression was enriched in leaves, roots and phloem, but relatively weak in xylem. Using split root systems, Fe deficiency in one portion of the root system could induce dramatic up-regulation of the PbCS1 expression in the Fe-sufficient part, suggesting that the PbCS1 expression was activated by systemic signals. In addition, supplying with NAA and exogenous auxin to the de-topped shoots could recover the Fe deficiency-induced up-regulation of the PbCS1 expression in the Fe-sufficient part of the root system. In contrast, NPA (an auxin transport inhibitor) application to the shoot tips arrested up-regulation of the PbCS1 expression in the untreated portion. The results suggested that Fe-deficiency-induced alterations of the PbCS1 expression were mediated by auxin.