Identification and characterization of a heat-stress induced gene in cabbage encodes a Kunitz type protease inhibitor

We have identified a heat-stress induced gene (BocHS1) by differential scre ening of a cDNA library constructed from Brassica oleracea var. capitata (c abbage) exposed to high temperature at 35 degrees C. Sequence analysis of B ocHS1 revealed that it encodes a putative protein related to 22 kDa drought and salt-induced proteins. These proteins exhibited high similarity to the Kunitz type of protease inhibitors. Northern blot analysis of coral RNA in dicates that a single transcript of approximately 1.3 kb was identified in heat-shocked plants. No transcript was detected in plants grown at low temp erature (20 degrees C). The level of transcript hybridizing to BocHS1 incre ased with 24-h exposure to high temperature. Further, a high level of trans cript was also noticed with the other cultivars that had been heat-shocked at 35 degrees C frdm 4 to 72 h. The level of gene expression was further mo nitored at a different range of temperature from 15 to 45 degrees C and the expression of this gene was noticed from 30, 35 and 40 degrees C. This gen e is also induced by drought but not by exogenous application of ABA or sal t-stress. Transferring plants from 35 degrees C. to low temperature (20 deg rees C) results in the loss of detectable transcript hybridizing to BocHS1. Hybridization of the heat-stress induced gene with genomic DNA revealed th ree copies and we suggest that BocHS1 is encoded by a small gene family in Brassica. The protein encoded by BocHS1 exhibits a new class of genes that are related to protease inhibitors; also, this is the first example of the Kunitz type of protease inhibitors induced in vegetative tissues during hea t-stress.