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<p>Abstract</p> <p>Background</p> <p>Plants respond to abiotic stress through complex regulation of transcription, including both transcriptional activation and repression. Dehydration-responsive-element binding protein (DREB)-type transcription factors are well known to play important roles in adaptation to abiotic stress. The mechanisms by which DREB-type transcription factors activate stress-induced gene expression have been relatively well studied. However, little is known about how DREB-type transcriptional repressors modulate plant stress responses. In this study, we report the functional analysis of RAP2.1, a DREB-type transcriptional repressor.</p> <p>Results</p> <p>RAP2.1 possesses an APETALA2 (AP2) domain that binds to dehydration-responsive elements (DREs) and an ERF-associated amphiphilic repression (EAR) motif, as the repression domain located at the C-terminus of the protein. Expression of <it>RAP2.1 </it>is strongly induced by drought and cold stress via an ABA-independent pathway. Arabidopsis plants overexpressing <it>RAP2.1 </it>show enhanced sensitivity to cold and drought stresses, while <it>rap2.1-1 </it>and <it>rap2.1-2 </it>T-DNA insertion alleles result in reduced sensitivity to these stresses. The reduced stress sensitivity of the plant containing the <it>rap2.1 </it>allele can be genetically complemented by the expression of <it>RAP2.1</it>, but not by the expression of EAR-motif-mutated <it>RAP2.1</it>. Furthermore, chromatin immunoprecipitation (ChIP) analysis has identified <it>Responsive to desiccation/Cold-regulated </it>(<it>RD/COR</it>) genes as downstream targets of RAP2.1 <it>in vivo</it>. Stress-induced expression of the <it>RD/COR </it>genes is repressed by overexpression of <it>RAP2.1 </it>and is increased in plants expressing the <it>rap2.1 </it>allele. In addition, RAP2.1 can negatively regulate its own expression by binding to DREs present in its own promoter. Our data suggest that RAP2.1 acts as a negative transcriptional regulator in defence responses to cold and drought stress in Arabidopsis.</p> <p>Conclusions</p> <p>A hypothetical model for the role of RAP2.1 in modulating plant responses to cold and drought is proposed in this study. It appears that RAP2.1 acts as a negative "subregulon" of DREB-type activators and is involved in the precise regulation of expression of stress-related genes, acting to keep stress responses under tight control.</p>