Two Transcription Factors, DREB1 and DREB2, with an EREBP/AP2 DNA Binding Domain Separate Two Cellular Signal Transduction Pathways in Drought- and Low-Temperature-Responsive Gene Expression, Respectively, in Arabidopsis
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Abstract
Plant growth is greatly affected by drought and low temperature. Expression of a number
of genes is induced by both drought and low temperature, although these stresses are
quite different. Previous experiments have established that a cis-acting element named
DRE (for dehydration-responsive element) plays an important role in both dehydration-
and low-temperature-induced gene expression in Arabidopsis. Two cDNA clones that encode
DRE binding proteins, DREB1A and DREB2A, were isolated by using the yeast one-hybrid
screening technique. The two cDNA libraries were prepared from dehydrated and cold-treated
rosette plants, respectively. The deduced amino acid sequences of DREB1A and DREB2A
showed no significant sequence similarity, except in the conserved DNA binding domains
found in the EREBP and APETALA2 proteins that function in ethylene-responsive expression
and floral morphogenesis, respectively. Both the DREB1A and DREB2A proteins specifically
bound to the DRE sequence in vitro and activated the transcription of the b-glucuronidase
reporter gene driven by the DRE sequence in Arabidopsis leaf protoplasts. Expression
of the DREB1A gene and its two homologs was induced by low-temperature stress, whereas
expression of the DREB2A gene and its single homolog was induced by dehydration. Overexpression
of the DREB1A cDNA in transgenic Arabidopsis plants not only induced strong expression
of the target genes under unstressed conditions but also caused dwarfed phenotypes
in the transgenic plants. These transgenic plants also revealed freezing and dehydration
tolerance. In contrast, overexpression of the DREB2A cDNA induced weak expression
of the target genes under unstressed conditions and caused growth retardation of the
transgenic plants. These results indicate that two independent families of DREB proteins,
DREB1 and DREB2, function as trans-acting factors in two separate signal transduction
pathways under low-temperature and dehydration conditions, respectively.