Tuesday, January 13, 2015
UmamiT amino acid facilitators are required for amino acid supply of sink tissues
Ulrich Z. Hammes
Cell Biology and Plant Physiology, University of Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany
Nitrogen is required by plants in large quantities and is often a growth-limiting factor. In vascular plants, reduced nitrogen is transported mainly in the form of amino acids. The cycling of amino acids between source and sink tissues is thought to mediate the communication of the nitrogen status between organs. In endogenous or pathogen-induced sink tissues, amino acids are used for metabolism or are consumed. Sink tissues, such as seeds, fruits or tubers, often represent the harvestable and edible portion of the plant. As some amino acids are essential, i.e. cannot be synthesized by humans, amino acid composition within a sink tissue is a crucial component of yield quality. Transporters that catalyze the export of amino acids from cells are strictly required for vascular loading and unloading but the molecular identity of the transporters was so far unknown. We have identified a plant-specific family of novel amino acid transporters, called UmamiTs. Members of this family are able to mediate amino acid transport along the electrochemical gradient and thus amino acid export. Expression pattern and localization of the UmamiTs we identified is consistent with a role in amino acid cycling and amino acid supply of sink tissues. We show that UmamiT transporters play a role in supplying amino acids to plant pathogenic root-knot nematodes. Furthermore, UmamiTs showed very specific expression patterns in various tissues of developing Arabidopsis seeds. umamit knock-out mutants fail to unload amino acids in fruits of Arabidopsis and accumulate free amino acids as a result. Our results suggest that UmamiT transporters are a critical component of long distance amino acid transport.
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