Nitrogen (N) is one of the most limiting soil-derived nutrients for plant growth and productivity. Therefore plants have evolved diverse and complex strategies for the uptake, assimilation and reallocation of N (Rentsch et al., 2007). Research on transport of organic N in plants has focused on translocation of amino acids, while transport of peptides, which are generated from stored or cellular proteins, has received less attention. It has been postulated that for recycling of protein N during senescence and germination, transport of peptides might be of equal or even greater importance than transport of amino acids. Moreover, there is evidence that peptide uptake and reallocation occurs during vegetative growth. During the last years several transporters for small peptides have been identified from Arabidopsis and other plant species (e.g. Frommer et al., 1994; Rentsch et al., 1995, Dietrich et al., 2004, Komarova et al., 2008, Paungfoo-Lonhienne et al., 2009). There is also evidence that plants can use protein as N source (Paungfoo-Lonhienne et al., 2008).
We recently produced the first evidence that di- and tripeptides are a N source for Arabidopsis, and we identified transporters responsible for the uptake of peptides from soil into roots (Komarova et al., 2008). We aim to further explore the physiological role of peptide uptake, transport and metabolism and elucidate mechanisms involved in regulation and targeting, and identify amino acid residues or regions required for substrate recognition. We will also examine plant peptide transporters in the broader evolutionary and ecological contexts.

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