Ion transport across biological membranes plays an important function in maintaining the ionic homeostasis within the cell and organelles for the well-functioning of a cell. High-affinity potassium transporters (HKT) are exclusively present in plants, involved mainly in salt tolerance. HKT’s are present from streptophyte algae to angiosperms, grouped in three clades with sub-families 1-2 separated from homologs present in bryophytes. In this work we identified a sole HKT transporter (PpHKT) present in the moss Physcomitrium patens; according to sequence analysis, it presents four Glycine residues in the pore region of the selectivity filter, similar to the ancestral structure of the related Trk/Ktr prokaryote K+-selective transporters. PpHKT has been characterized as a K+ and Na+ transporter, but its physiological role in the moss is not clear. We characterized the phenotype for the Pp∆hkt mutant along its life cycle, observing that the mutation has pleiotropic effects, stimulating gametophore growth, decreasing chlorophyll content and null production of sporophytes, suggesting an essential role in the development and metabolism in the moss. PpHKT is located at the chloroplast and is expressed in all tissues, including reproductive structures. RNA-seq analysis of the mutant revealed the down expression of genes involved in photosynthesis and spermatogenesis, while genes involved in ion and metal membrane transport are up-regulated. These results show the importance of HKT transporter in plant development rather than in salinity tolerance in plants. Additional results will be presented and discussed.