Transgenic plants with chilling resistance (desaturation of fatty acids)

Many of our crop plants (e.g. rice, maize, soybean) are injured or killed by exposure to low non-freezing temperatures in the range of O-I5°C. They are described as chilling-sensitive plants and carry lipids with only saturated fatty acids. It has been shown that presence of even one double bond in one of the 16 or 18 carbon saturated fatty acids found in the lipids, may lead to resistance against injury by low temperature.

Except these three enzymatic activities leading to desaturation of fatty acids, no other fatty acid esterified to other lipids or to other positions of glycerol, can be desaturated in higher plants. Thus the scope of introducing double bond for resistance against low temperature becomes limited, if genes for higher plants only need to be exploited.

Nevertheless some successful efforts have been made by utilizing genes from higher plants. These efforts include the following. (i) saturation of the level of PG (a minor component of membrane lipids), was slightly reduced to 94%, in transgenic tobacco plants carrying a gene for glycerol-3-phosphate acyltransferase from Arabidopsis thaliana, which itself is chilling resistant.

Therefore, more recently (a report published in 1996), a broad-specificity  Δ desaturase  gene from a cyanobacterium (Anacyctis nidulans) was used, that was capable of introducing a cos-double bond at Δ9 position of both 16 and 18 carbon saturated fatty acids linked to membrane lipids. The gene was successfully introduced and its expression driven by CaMV 35S promoter.

The enzyme was targeted into the plastids by the transit peptide of pea Rubisco small subunit. The transgenic tobacco plants thus produced had a highly reduced level of saturated fatty acid content in most membrane lipids and exhibited a significant increase in chilling resistance.