PbrPOE21inhibits pear pollen tube growth in vitro by altering apical reactive oxygen species content

Main conclusion Genome-wide identification, tissue-specific expression analysis and functional characterization of selected genes containing the pear Pollen Olea europaea I domain reveal their roles in pollen tube growth. Genes containing the Pollen Olea europaea I (POE) domain play crucial roles in diverse growth and developmental processes. Nevertheless, the specific functions of POE family members in progression of pollen tube growth (PTG) remain uncharacterized. We identified 45PbrPOEgenes in the pear (Pyrus bretschneideri) genome, clustered into seven subclasses.PbrPOEgenes contained 1 to 11 exons and 0 to 10 introns, with exon/intron structure mostly conserved within each subclass. Whole-genome duplication has mainly contributed to the duplication pattern ofPbrPOEgenes in pear. Expression profiles of 45PbrPOEgenes in 12 different pear tissues revealed that sixPbrPOEgenes (PbrPOE6,12,21,29,35and41) of subclass B were highly expressed during the growth of the pear pollen tube in vitro.PbrPOE21was selected for further functional analysis on the basis of its high and differential expression pattern in pollen. Antisense oligodeoxynucleotide assays demonstrated that PTG was augmented in vitro whenPbrPOE21expression was significantly inhibited. Moreover, pollen tube length in vitro was reduced whenPbrPOE21was transitorily over-expressed using particle bombardment technology. Exogenous PbrPOE21 recombinant protein inhibited PTG in vitro at an optimum concentration of 1.8 mu M. PbrPOE21 also affected reactive oxygen species content in the pear pollen tube apex. We suggest that PbrPOE21 inhibits PTG in vitro by altering apical reactive oxygen species content.