Cloning and functional characterisation of a peptide transporter expressed in the scutellum of barley grain during the early stages of germination

Abstract

A peptide transport gene (HvPTR1) expressed in the scutella of germinating barley grain has been cloned by an RT-PCR approach. Sequence analysis of the full length cDNA (2260 bp) revealed an open reading frame encoding a 579 amino acid protein of predicted molecular mass 63 kDa, which displayed 58% identity to the Arabidopsis thaliana peptide transporter AtPTR2-B. Expression of HvPTR1 in Xenopus laevis oocytes conferred a 48-fold increase in alanyl-[14C]phenylalanine uptake relative to water injected oocytes, confirming the function of HvPTR1 as a peptide transporter. HvPTR1 expression was detectable only in the scutellum of the germinating barley grain, with no transcript found in roots, shoots or the embryo axis. Transcript levels increased rapidly from 6 to 24 h imbibition, correlating with the development of peptide transport activity in the barley scutellum. Peptide transport provides a significant source of organic nitrogen to the barley embryo for use in germination and growth processes associated with the early stages of seedling development. The temporal and spatial pattern of HvPTR1 expression is consistent with a central role for HvPTR1 in the transport of peptides in the germinating barley grain.