Cloning of Genes Encoding Auxin-Binding Proteins (ABP19/20) from Peach: Significant Peptide Sequence Similarity with Germin-Like Proteins

An auxin-binding protein (ABP) was previously isolated from shoot apices of peach trees to homogenity on standard SDS-PAGE. Analysis of low-bis SDS-PAGE and direct peptide sequencing of purified peach ABP demonstrated that the ABP was composed of two types of polypeptides (designated ABP19 and ABP20). Several cDNA and genomic clones which encode peach ABPs were obtained and analysed. We found that there are at least three classes of ABPs in the peach genome. Open reading frames of these ABPs were 627 bp, predicting a 209 amino acid polypeptide of 22 kDa. An N-terminal hydrophobic signal sequence of 18 amino acids and a putative N-glycosylation site at N60-T-T/S were deduced. Homology search analysis revealed that ABP19 is highly homologous to proteins related to the germin family. The deduced amino acid sequence of ABP19 showed very low overall sequence homology with ABP1, an ABP isolated from maize coleoptile, but it contained a small region which shared 40% homology with a putative auxin binding site in ABP1 (BoxA). In addition, the sequence surrounding the region is highly conserved among peach ABPs and the germin family.