Financial support: Grants from Canadian Bacterial Diseases Network, Natural Science and Engineering Research Council of Canada, and American Gene Therapy Inc.

Keywords: branched chain alpha-oxo acid decarboxylase, cold tolerance, gene expression, transgenic tomato plants.

Engineering of higher plants for increased cold tolerance requires a chemical modification of membrane fluidity in both organelles and cytoplasm of plant cells. A small number of microorganisms use branched chain fatty acids as their membrane constituents to maintain membrane fluidity, instead of unsaturated fatty acids. One of the key enzymes facilitating synthesis of branched chain fatty acids in Bacillus subtilis 168s is the branched chain alpha-oxo acid decarboxylase. To examine the role of branched chain fatty acids in plants and the potential for low temperature tolerance, the A and B genes encoding the alpha and beta polypeptides, respectively, of the branched chain alpha-oxo acid decarboxylase were introduced into the genome of tomato plants. The mas promoters in the plant expression vector system facilitated the expression of the A and B genes. Transgenic plants were regenerated and shown to produce both the alpha and beta polypeptides. Comparative analysis of a small number of transgenic tomato plants and non-transformed control plants grown at 4ºC showed enhanced cold tolerance in the transformed plants. These findings, if confirmed by a larger scale analysis, suggest a potential role for branched chain fatty acids as a protective mechanism for growth of plants under sub optimal temperatures.