Molecular cloning of a Brassica napus cysteine protease gene inducible by drought and low temperature stress

We have identified a drought-inducible gene in Brassica napus, bcp-15, which encodes a putative protein with significant amino acid similarity to wound and stress-induced plant cysteine proteases. We detected basal levels of bcp-15 transcript in leaves of nonstressed B. napus plants. Subjecting plants to drought resulted in a maximum 3-fold increase in expression at 63% relative water content (RWC), while further dehydration resulted in decreased levels of expression. Low temperature caused the greatest accumulation of bcp-15 transcript; an 8.5-fold increase was seen after 1 day of exposure to 4°C. After 4 days of exposure, transcript levels decreased to 6.4-fold over basal levels. These results suggest that the encoded BCP15 protease is required during the early stages of stress response. Exposure to 40°C heat shock resulted in a moderate increase in expression, although transcript levels were less than those seen for dehydrated or low-temperature-treated plants. Addition of the plant hormone abscisic acid had only a minor effect on bcp-15 transcript levels. High salt caused a decrease, not an increase, in bcp-15 expression over basal levels. These results suggest that bcp-15 responds to specific conditions of stress and is not simply an adaptation to general osmotic stress.