Constitutive expression of DaCBF7, an Antarctic vascular plant Deschampsia antarctica CBF homolog, resulted in improved cold tolerance in transgenic rice plants

Abstract

<em>Deschampsia antarctica</em> is an Antarctic hairgrass that grows on the west coast of the Antarctic penin-sula. In this report, we have identified and characterized a transcription factor, <em>D. antarctica</em> C-repeatbinding factor 7 (DaCBF7), that is a member of the monocot group V CBF homologs. The protein con-tains a single AP2 domain, a putative nuclear localization signal, and the typical CBF signature. DaCBF7,like other monocot group V homologs, contains a distinct polypeptide stretch composed of 43 aminoacids in front of the AP2 motif. DaCBF7 was predominantly localized to nuclei and interacted withthe C-repeat/dehydration responsive element (CRT/DRE) core sequence (ACCGAC) in vitro. DaCBF7 wasinduced by abiotic stresses, including drought, cold, and salinity. To investigate its possible cellular rolein cold tolerance, a transgenic rice system was employed. DaCBF7-overexpressing transgenic rice plants(Ubi:DaCBF7) exhibited markedly increased tolerance to cold stress compared to wild-type plants withoutgrowth defects; however, overexpression of DaCBF7 exerted little effect on tolerance to drought or saltstress. Transcriptome analysis of a Ubi:DaCBF7 transgenic line revealed 13 genes that were up-regulatedin DaCBF7-overexpressing plants compared to wild-type plants in the absence of cold stress and in short-or long-term cold stress. Five of these genes, dehydrin, remorin, Os03g63870, Os11g34790, and Os10g22630,contained putative CRT/DRE or low-temperature responsive elements in their promoter regions. Theseresults suggest that overexpression of DaCBF7 directly and indirectly induces diverse genes in transgenicrice plants and confers enhanced tolerance to cold stress.