Characterization of the Chloride Channel-Like, AtCLCg, Involved in Chloride Tolerance in Arabidopsis thaliana.

In plant cells, anion channels and transporters are essential for key functions such as nutrition, ion homeostasis and resistance to biotic or abiotic stresses. We characterized AtCLCg, a member of the chloride channel (CLC) family in Arabidopsis localized in the vacuolar membrane. When grown on NaCl or KCl,atclcgknock-out mutants showed a decrease in biomass. In the presence of NaCl, these mutants overaccumulate chloride in shoots. No difference in growth was detected in response to osmotic stress by mannitol. These results suggest a physiological function of AtCLCg in the chloride homeostasis during NaCl stress. AtCLCg shares a high degree of identity (62%) with AtCLCc, another vacuolar CLC essential for NaCl tolerance. However, theatclcc atclccgdouble mutant is not more sensitive to NaCl than single mutants. As the effects of both mutations are not additive, gene expression analyses were performed and revealed that: (i)AtCLCgis expressed in mesophyll cells, hydathodes and phloem whileAtCLCcis expressed in stomata; and (ii)AtCLCgis repressed in theatclccmutant background, and vice versa. Altogether these results demonstrate that both AtCLCc and AtCLCg are important for tolerance to excess chloride but not redundant, and form part of a regulatory network controlling chloride sensitivity.

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