In many temperate plants, cold acclimation, which is achieved by exposure to non-freezing, low temperatures, results in a significant increase in freezing tolerance as a consequence of the physicochemical stabilization of the plasma membrane, which is the primary determinant of the cell survival under freezing conditions. Although the causal relationship between an increase in freezing tolerance and changes in plasma membrane lipid composition during cold acclimation has been well established, there have been only a few studies on the role of plasma membrane proteins in acquirement of freezing tolerance To investigate it, we have determined the effect of cold-responsive plasma membrane proteins on the freezing tolerance of Arabidopsis plants. One of the cold-responsive plasma membrane proteins that has domains with high similarity to proteins in the lipocalin family (Arabidopsis lipocalin, AtLCN) was chosen. Transgenic Arabidopsis plants that overexpress AtLCN showed enhanced freezing tolerance compared to wild type plants. Using protein-lipid overlay assay, we found that recombinant AtLCN protein had a high affinity for acidic phospholipids found in the plasma membrane. Taken together, AtLCN protein may contribute to increase in freezing tolerance by accumulating adjacent to the plasma membrane and binding to the acid phospholipids.
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