Proteostasis of the A.thaliana TPK/KCO channels

Plant channels control the vectorial transport of fluid, solutes and electrolytes. To perform these functions, channels must be targeted, sorted and retained at the appropriate membrane and be subjected to regulated turnover. We are studying the proteostasis of the five tandem-pore (TPK1-5) and the single one-pore (KCO3) K+ channels of A. thaliana. Transient or transgenic expression of GFP fusions, or localization of endogenous proteins showed localizations at the tonoplast, plasma membrane, thylakoid membranes, as well as unidentified intracellular structures, depending on the channel. With the aim of clarifying the situation, we have first compared in silico the N-termini of TPKs/KCO. We found that AtTPK3, 5 and 2 contain N-terminal regions with similar features and putative chloroplast/mitochondrial presequences. To verify in vivo our in silico prediction, TPKs/KCO-N-termini::GFP fusions have been expressed. We also identified a putative PDZ-binding motif of class 1 at the C-terminus of KCO3. The role of this motif in KCO3 turnover has been analysed.