ARABIDOPSIS-THALIANA COR15B, AN APPARENT HOMOLOG OF COR15A, IS STRONGLY RESPONSIVE TO COLD AND ABA, BUT NOT DROUGHT

We previously described a cold-regulated (cor) gene from Arabidopsis t haliana, cor15a (formerly cor15), that encodes a 15 kDa polypeptide th at is targeted to chloroplasts (C. Lin and M. Thomashow, Plant Physiol 99 (1992): 519-525). Here we describe an apparent homologue of cor15a , cor15b. col15b is located immediately downstream from cor15a (within 1 kb) and has the same relative 5' to 3' orientation as cor15a. The p redicted coding regions for the two genes are 82% identical at the nuc leic acid sequence level. Transcripts for cor15b, like those of cor15a , increase dramatically in response to low temperature and exogenous a pplication of ABA. However, only cor15a transcripts accumulate to high levels in response to drought. The cor15a/cor15b gene pair is the thi rd case in which A. thaliana cold-regulated genes have been found to e xist as tandem gene pairs with the members of each pair being differen tially regulated.