Expression of wheat Peptide TRansporter 2.1 (TaPTR2.1) during early seed germination

Peptide TRansporters (PTRs) translocate nitrogen (N)-containing substances across cellular membranes. In Arabidopsis thaliana, the seed-abundant, tonoplast-localized AtPTR2 protein is involved in the regulation of water status during seed germination and is negatively regulated by ABA INSENSITIVE4 (ABI4). A survey of publicly available whole-genome sequencing and RNA-seq data revealed that the genomes of hexaploid wheat (Triticum aestivum L.) harbors three homologs of the AtPTR2 gene, TaPTR2.1, TaPTR2.2, and TaPTR2.3, and transcripts of TaPTR2.1 are detected both in dry and germinating seeds, similar to AtPTR2. However, the functional role of TaPTR2.1 during seed germination has not yet been characterized. In the present study, changes in TaPTR2.1 transcript levels were investigated in the wheat cultivar Keumgang in response to phytohormone, sugar, and osmoticum treatments. A transient increase in the transcript level of TaPTR2.1 during seed germination was significantly lowered by abscisic acid (ABA) and PEG4000 treatments. Further, overexpression of the TaPTR2.1 gene under the control of the Cauliflower mosaic virus 35S promoter in the Arabidopsis ptr2 mutant rescued the delayed seed germination phenotype by restoring the seed water status. Together, these results suggest that TaPTR2.1 regulates the water status of wheat seeds during germination in an ABA-dependent manner.