Chilling tolerance in arabidopsis involves ALA1, a member of a new family of putative aminophospholipid translocases

The lipid composition of membranes is a key determinant for cold tolerance, and enzymes that modify membrane structure seem to be important for low-te mperature acclimation. We have characterized ALA1 (for aminophospholipid AT Pase1), a novel P-type ATPase in Arabidopsis that belongs to the gene famil y ALA1 to ALA11. The deduced amino acid sequence of ALA1 is homologous with those of yeast DRS2 and bovine ATPase II, both of which are putative amino phospholipid translocases. ALA1 complements the deficiency in phosphatidyls erine internalization into intact cells that is exhibited by the drs2 yeast mutant, and expression of ALA1 results in increased translocation of amino phospholipids in reconstituted yeast membrane vesicles. These lines of evid ence suggest that ALA1 is involved in generating membrane lipid asymmetry a nd probably encodes an aminophospholipid translocase. ALA1 complements the cold sensitivity of the drs2 yeast mutant. Downregulation of ALA1 in Arabid opsis results in cold-affected plants that are much smaller than those of t he wild type. These data suggest a link between regulation of transmembrane bilayer lipid asymmetry and the adaptation of plants to cold.