Localization of ion transport-related genes on E. carolleeae chromosomes and hypothetical models of ion uptake from fresh water

A. Ion transport-related genes were mapped onto the four E. carolleeae chromosomes. All vertical lines represent the 490 genes with ion (cation and anion) transporting function based on genome annotation. The vertical lines marked with colored dots represent the 80 key ion transport-related genes, which showed evolutionary shifts in gene expression and/or signatures of selection in prior studies, and are likely involved in the hypothetical models of ion uptake (in B and C, adapted from [50]). The vertical dashed lines marked with stars indicate the positions of centromeres based on the Hi-C contact map (Figure 1D, Figure S12). B. Hypothetical model 1 of ion uptake from freshwater environments. VHA generates an electrochemical gradient by pumping out protons, to facilitate uptake of Na⁺ through an electrogenic Na⁺ transporter (likely NHA). CA produces protons for VHA. C. Hypothetical model 2 of ion uptake from freshwater environments. An ammonia transporter Rh protein exports NH₃ out of the cell and then this NH₃ reacts with H⁺ to form $NH4+$⁠. The resulting deficit of extracellular H⁺ concentrations causes NHE to export H⁺ in exchange for the import of Na⁺. CA produces protons for NHE. These models are not comprehensive for all tissues or taxa and are not mutually exclusive. NKA-α, Na⁺/K⁺-ATPase α subunit; NKA-β, Na⁺/K⁺-ATPase β subunit; NHE, Na⁺/H⁺ exchanger; NHA, Na⁺/H⁺ antiporter; NKCC, Na⁺,K⁺,Cl⁻ cotransporter; CA, carbonic anhydrase; AMT, ammonia transporter; Rh, Rh protein; SLC4, solute carrier family 4 of bicarbonate transporters; AE, anion exchanger; NBC, Na⁺,$HCO3−$ cotransporter; NDCBE, Na⁺-driven Cl⁻/$HCO3−$ exchanger; VHA subunits, subunits of vacuolar-type H⁺ ATPase; Nach, sodium channel.