Two New Members of CsFEXs Couple Proton Gradients to Export Fluoride and Participate in Reducing Fluoride Accumulation in Low-Fluoride Tea Cultivars

Abstract

The accumulation of fluoride in tea leaves from various cultivars exhibits significant differences. However, the molecular basis and mechanism remain largely unknown. Here, we reported that two genes of <i>CsFEX</i> (fluoride export genes in <i>Camellia sinensis</i>), <i>CsFEX1</i> and <i>CsFEX2</i>, transport fluoride out of cells, alleviate the cellular fluoride toxin, and rescue the yeast mutant (<i>FEX1ΔFEX2Δ</i>) and <i>Arabidopsis</i> mutant (<i>fex</i>), as their efflux activities are coupled with proton gradients. Further analysis found that CsFEX1 and CsFEX2 localize to the plasma membrane both in yeast and <i>Arabidopsis</i> cells. CsFEX2 is more effective to reduce fluoride toxicity in yeast and <i>Arabidopsis</i> compared with CsFEX1 even at low pH. <i>CsFEX2</i> induced by fluoride treatment is around tenfold higher in a low-fluoride cultivar (Yunkang 10) than that in a high-fluoride cultivar (Pingyang Tezaocha), suggesting that <i>CsFEX2</i> possibly plays a critical role in reducing fluoride accumulation in tea leaves.