Regulation of nitrogen transporters and retranslocation of nitrogen during senescence

Our previous studies have shown that high-affinity urea uptake relies on one transporter called DUR3, while the uptake of ammonium is mediated by six AMT-type ammonium transporters. These transporters are regulated at multiple levels, and specific regulatory features have been identified at the transcriptional and post-transcriptional levels as well as at the post-translational level, e.g. by the allosteric regulation of AMT subunits in homo- and heterotrimers (Yuan et al., 2007; Loqué et al., 2007; Lanquar et al., 2009). Uptake studies with 15NH4+ in multiple AMT mutants and localization studies with GFP-labeled transport proteins have further shown that the contribution of individual transporters depends on their biochemical properties and their cell type-specific localization in the root. This is to propose “job sharing” principle among AMT isoforms (Loqué et al., 2006; Yuan et al., 2007). Ongoing investigations focus on the elucidation of further regulatory mechanisms of AMT transporters.

In a coupled approach we investigate the role of transporters for different nitrogenous compounds for nitrogen re-translocation during leaf senescence. This implies the understanding of senescence processes in leaves and roots as well as how re-translocation processes are coupled to developmental signals such as phytohormones. In a field-based approach we establish screening methods for the identification of barley genotypes with high retranslocation efficiency.

 

Anne Bohner, Ralf Sammler, Alberto Laginha, Zhaojun Liu, Lisa Unrath, Barbara Kettig