Characterization of the <i>ERP</i> gene family in <i>Arabidopsis thaliana</i>

Plant genomes encode numerous proteins with obscure features (POFs) that lack recognized domains or motifs. However, there is little functional information for POFs even in <i>Arabidopsis</i> because biochemical, physiological, and genetic assay are required for the functional annotations of POFs. Here, we identified a small gene family, the endoplasmic reticulum-localized POF (ERP) family, in <i>Arabidopsis</i>. Phylogenetic analysis revealed that the number of ERP family members was conserved in the plant kingdom, suggesting strong selective pressure was imposed on ERP family during plant evolution. No recognizable domains were identified in the predicted ERP proteins, except for the N-terminal signal peptide. ERPs were found to be widely expressed during <i>Arabidopsis</i> development and showed endoplasmic reticulum localization. It was reported that <i>ERP1</i> is an inositol-1,4,5-trisphosphate 5-phosphatase (5PTase), but <i>ERP1</i> could not substitute for <i>At5PTase12</i> in precocious pollen germination, indicating that <i>ERP1</i> did not have the similar functions as <i>At5PTase12</i> in inositol 1,4,5-trisphosphate [Ins(1,4,5)<i>P3</i>] metabolism. Further studies are needed to dissect the functions of ERP family proteins in <i>Arabidopsis</i> development.