A family of putative chloride channels from Arabidopsis and functional complementation of a yeast strain with a CLC gene disruption

We have cloned four novel members of the CLC family of chloride channels from Arabidopsis thaliana. The four plant genes are homologous to a recently isolated chloride channel gene from tobacco (CLC-Nt1; Lurin, C., Geelen, D., Barbier-Brygoo, H., Guern, J., and Maurel, C. (1996) Plant Cell 8, 701-711) and are about 30% identical in sequence to the most closely related CLC-6 and CLC-7 putative chloride channels from mammalia. AtCLC transcripts are broadly expressed in the plant. Similarly, antibodies against the AtCLC-d protein detected the protein in all tissues, but predominantly in the silique. AtCLC-a and AtCLC-b are highly homologous to each other ( approximately 87% identity), while being approximately 50% identical to either AtCLC-c or AtCLC-d. None of the four cDNAs elicited chloride currents when expressed in Xenopus oocytes, either singly or in combination. Among these genes, only AtCLC-d could functionally substitute for the single yeast CLC protein, restoring iron-limited growth of a strain disrupted for this gene. Introduction of disease causing mutations, identified in human CLC genes, abolished this capacity. Consistent with a similar function of both proteins, the green fluorescent protein-tagged AtCLC-d protein showed the identical localization pattern as the yeast ScCLC protein. This suggests that in Arabidopsis AtCLC-d functions as an intracellular chloride channel.