DRE because a transgenic plant constitutively expressing CBF was shown to express many DRE-con-
trolled proteins and to have a general elevation in cold tolerance [165].
DREs have been found in the promoters of genes generally associated with inducibility by low wa-
ter status or pathway IV and negatively correlated with inducibility by ABA. In fact, several DREBs not
corresponding to CBFs also bind to the DRE. They are dehydration inducible but are not regulated by low
temperature. It is not known whether these DREBs constitute a portion of the poorly defined pathway III,
but that would be a reasonable speculation.
An additional level of control has been demonstrated by Ishitani et al. [166], who indicated that path-
way IV may not be totally independent of ABA, as shown by some intriguing transgenic plant analyses
as well as by the observation of some ABA induction by low temperatures [140,161]. Ishitani et al. [167]INDUCTION OF PROTEINS IN RESPONSE TO STRESSES 671
Figure 2 Decreased water status signal transduction model. ABA, abscisic acid; ABI, abscisic acid insensi-
tive (a phosphatase); JA, jasmonic acid; cADPR, cyclic ADP-ribose; PL C, phospholipase C; IP3, inositol
1,4,5-triphosphate; bZIP, transcription factor with bZIP motif; ABRE, abscisic acid response element; DREB,
drought-responsive element binding; ICE, inducer of CBF expression; CBF, C-repeat/DRE binding factor;
MAP, mitogen-activating protein. Solid lines indicate strong evidence for the pathway, (--) indicates an in-
hibitory pathway of unknown mechanism, (—-) indicates an incompletely understood pathway, (--) indicates
a speculative pathway. (Adapted from Refs. 153, 159, 160, 164, 166, 167.)