The tonoplast-localized K+,Na+/H+ exchangers NHX1 and NHX2 of Arabidopsis mediate the accumulation of K+ into the vacuole of cells, thereby increasing the osmotic potential, water uptake and the turgor pressure necessary for cell expansion and growth, as well as for regulation of vacuolar pH. However, little is known about how Arabidopsis thaliana NHX activity is regulated by intrinsic structural features and by ancillary cytosolic factors. We conducted phylogenetic analysis and computational modeling of the NHX1 protein that allowed us to identify essential structural domains and amino acid residues putatively involved in ion transport, cation coordination, and pH sensing of NHX1. Point-mutation alleles of these relevant residues were generated, and their impact on the biochemical activity and pH dependence of NHX1 by functionality tests in yeast and in vitro ion transport assays was studied. Computational and biochemical analyses also suggested the presence of a calmodulin-binding domain comprising two α-helices at the C-termini of NHX1 and NHX2. We demonstrated the importance of the putative calmodulin-binding domain in NHX1 activity by functional analyses in S. cerevisiae, as well as the interaction of NHX1 with CalModulin-Like18 (CML18) by BiFC and Y2H. Our results evidence the fine-tuning of NHX1 and/or NHX2 activity in response to developmental and environmental cues. In addition, we expect to unravel the biochemical mechanisms for pH sensing and regulation of these critical K+ transporters of Arabidopsis.

Conferencia presentada en la 29th International Conference on Arabidopsis Research (2018) ICAR 2018 25-29 June 2018, Turku, Finland

Peer reviewed