Role of Oligopeptide Transport in Plant Growth and Development

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Peptide transport is a widespread phenomenon exemplified by the translocation of peptides 2-6 residues in length across the plasma membrane in an energy-dependent and saturable manner. Peptide transporters fall into three families; the ATP binding cassette family (ABC transporters), the peptide transporter (PTR) family (transporting di- and tripeptides) and the recently described oligopeptide transporter (OPT) family. Completion of the Arabidopsis genome revealed that this plant possesses 10-fold more predicted peptide transporters than other sequenced organisms. For example, there are 52 predicted members of the PTR family and 9 putative members of the OPT family of peptide transporters. The OPT family members mediate the uptake of tetra- and pentapeptides. Recent results indicated that an AtOPT3::T-DNA mutant is defective in embryo formation in the developing seed. Examination of the opt3 embryo showed that development was blocked at the 8-cell stage. Together, these data strongly suggest that peptide transporters play very important, unexplored roles in plant growth and development. The proposed research seeks to define the physiological role for each of the Arabidopsis OPT peptide transporters. This will be done by examining the peptide transport activity of these proteins expressed in yeast and in Xenopus oocytes. Reverse genetics will be used to obtain plants defective in transporter function. Mutants will be characterized with regard to their growth and developmental (e.g., embryo) phenotype, as well as their ability to transport peptides. The cellular localization of each protein will be examined by expressing epitope-tagged proteins in transgenic plants. This research may lead to the recognition of new signaling pathways or avenues of nutrient circulation, which are critical to normal plant growth and development.Broader Impact: Research and education will be integrated in the project by the involvement of undergraduates, graduate students and postdoctoral associates. Participation of under-represented groups in science will be increased by interfacing with well established programs on the University of Missouri campus. Infrastructure will be improved by the purchase of needed electrophysiology equipment, which will serve as a campus-wide resource.The Molecular Biochemistry and Integrative Plant Biology Programs jointly fund this project.