9.B.60 The Glutamine Dumper 1 (GDU1) Family
Phloem and xylem transport of amino acids involves two steps: export from one cell type to the apoplasm, and subsequent import into adjacent cells. High-affinity import is mediated by proton/amino acid cotransporters, while the mechanism of export remains unclear. Enhanced expression of the plant-specific type I membrane protein Glutamine Dumper1 (GDU1) has previously been shown to induce the secretion of glutamine from hydathodes and increased amino acid content in leaf apoplasm and xylem sap. Tolerance to low concentrations of amino acids and transport analyses demonstrated that net amino acid uptake is reduced in the glutamine-secreting GDU1 overexpressor gdu1-1D (Pratelli et al., 2010). The net uptake rate of phenylalanine decreased over time, and amino acid net efflux was increased in gdu1-1D compared with the wild type.
Independence of the export from proton gradients and ATP suggested that overexpression of GDU1 affects a passive export system. Each of the seven A. thaliana GDU genes led to similar phenotypes, including increased efflux of a wide spectrum of amino acids. Differences in expression profiles and functional properties suggested that the GDU genes fulfill different roles in roots, vasculature, and reproductive organs. Taken together, the GDUs appear to stimulate amino acid export by activating nonselective amino acid facilitators. GDU1 may either fuction as a channel or stimulate the activities of other exporters (Pratelli et al., 2010). It could be a subunit of an amino acid exporter because it seems to stimulate amino acid export by activating nonselective amino acid facilitators. Required for the interaction with the RING-type E3 ubiquitin-protein ligase LOG2 to fulfill its function. Plays a role in the Gln export at hydathodes, at xylem parenchyma into xylem sap and from mesophyll into leaf apoplasm (Yu et al. 2015).