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.