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 similari ty to wound and stress-induced plant cysteine proteases. We detected b asal levels of bcp-15 transcript in leaves of nonstressed B. napus pla nts. Subjecting plants to drought resulted in a maximum 3-fold increas e in expression at 63% relative water content (RWC), while further deh ydration resulted in decreased levels of expression. Low temperature c aused the greatest accumulation of bcp-15 transcript; an 8.5-fold incr ease was seen after 1 day of exposure to 4 degrees C. After 4 days of exposure, transcript levels decreased to 6.4-fold over basal levels. T hese results suggest that the encoded BCP15 protease is required durin g the early stages of stress response. Exposure to 40 degrees C heat s hock resulted in a moderate increase in expression, although transcrip t levels were less than those seen for dehydrated or low-temperature-t reated 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 result s suggest that bcp-15 responds to specific conditions of stress and is not simply an adaptation to general osmotic stress.