Genome-wide identification of Nitrate Transporter 1/Peptide Transporter Family (NPF) genes in pear (Pyrus bretschneideri) and functional characterization of PbNPF5.7 in fire blight.

The Nitrate Transporter 1/Peptide Transporter family (NPF) plays a vital role in transporting a wide range of diverse mobile substrates, including nitrate, peptides, amino acids, dicarboxylates, malate, glucosinolates, indole-3-acetic acid (IAA), abscisic acid (ABA), and jasmonic acid (JA). While systematic characterization of NPF family genes has been achieved in model plants like Arabidopsis and rice, as well as in horticultural crops such as tomato and apple, their orthologs in Pyrus bretschneideri have not been thoroughly investigated. In this study, we identified 85 PbNPF genes in genome through phylogenetic and genomic analyses. Chromosomal location analysis revealed that 82 genes are distributed across 17 chromosomes, while three genes possessing ambiguous localization. Synteny analysis revealed that the expansion of this gene family was mostly caused by whole genome duplication events. Numerous hormone-responsive elements linked to biotic and abiotic stress responses were found using promoter cis-acting element analysis. Several PbNPF genes were markedly down-regulated after Erwinia amylovora infection, according to transcriptome data and qRT-PCR results. Subcellular localization confirmed that PbNPF5.7 is a plasma membrane-localized protein. Notably, PbNPF5.7 acts as a negative regulator of fire blight resistance: silencing PbNPF5.7 markedly enhances resistance to Erwinia amylovora by reducing ROS accumulation and increasing the activities of multiple defense-related enzymes, whereas overexpression of PbNPF5.7 in tobacco significantly increases susceptibility to fire blight. This study offers the first genome-wide characterization of the NPF family in pear and identifies PbNPF5.7 as a negative regulator of fire blight resistance. These findings suggest that members of the pear NPF family may play crucial roles in disease resistance.