CLONING AND FUNCTIONAL-CHARACTERIZATION OF A PEPTIDE TRANSPORTER EXPRESSED IN THE SCUTELLUM OF BARLEY-GRAIN DURING THE EARLY STAGES OF GERMINATION

A peptide transport gene (HvPTR1) expressed in the scutella of germina ting barley grain has been cloned by an RT-PCR approach. Sequence anal ysis 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 trans porter AtPTR2-B. Expression of HvPTR1 in Xenopus laevis oocytes confer red a 48-fold increase in alanyl-[C-14]phenylalanine uptake relative t o water injected oocytes, confirming the function of HvPTR1 as a pepti de transporter. HvPTR1 expression was detectable only in the scutellum of the germinating barley grain, with no transcript found in roots, s hoots or the embryo axis. Transcript levels increased rapidly from 6 t o 24 h imbibition, correlating with the development of peptide transpo rt activity in the barley scutellum. Peptide transport provides a sign ificant source of organic nitrogen to the barley embryo for use in ger mination and growth processes associated with the early stages of seed ling development. The temporal and spatial pattern of HvPTR1 expressio n is consistent with a central role for HvPTR1 in the transport of pep tides in the germinating barley grain.