Friend or Foe? Chloride patterning in halophytes

In this opinion article, we challenge the traditional view that breeding for reduced Cl⁻ uptake would benefit plant salinity tolerance. A negative correlation between shoot Cl⁻ concentration and plant biomass does not hold for halophytes – naturally salt tolerant species. We argue that, under physiologically relevant conditions, Cl⁻ uptake requires plants to invest metabolic energy, and that the poor selectivity of Cl⁻-transporting proteins may explain the reported negative correlation between Cl⁻ accumulation and crop salinity tolerance. We propose a new paradigm: salinity tolerance could be achieved by improving the selectivity of some of the broadly selective anion-transporting proteins (e.g., for NO₃⁻ > Cl⁻), alongside tight control of Cl⁻ uptake, rather than targeting traits mediating its efflux from the root.