Characterization of a cold responsive HbICE1 gene from rubber trees

A novel cold responsive HbICE1 gene from Hevea brasiliensis was identified, and its function as a transcriptional factor in cold stress responses was further analyzed. The inducers of CBF expression (ICEs) play a crucial role in the response of plants to cold stress. To date, information is limited about the ICE genes from rubber trees (Hevea brasiliensis Muell. Arg.), a tropical woody plant. In this study, an ICE homologuous gene, referred to as HbICE1, was isolated and characterized by a combination of molecular and physiological techniques and bioinformatics analyses. The full-length cDNA of HbICE1 was 1806-bp in length and contained a 1617 bp open reading frame (ORF) encoding a putative protein of 538 amino acids. The predicted HbICE1 harbored S-rich, bHLH and ACT-like domains that were conserved in ICE1 orthologs from Arabidopsis and other plant species. Phylogenetic analysis demonstrated that HbICE1 was closely related to MeICE1 and RcICE1 as well as PeICE1, MdICE1 and PuICE1. It harbored transcriptional activity and nucleus localization. qRT-PCR analysis showed that HbICE1 was mainly expressed in leaves and stems under natural conditions. Its expression was significantly up-regulated in the leaves of the cold-resistant rubber tree clone ‘93-114’ in response to cold stress by comparison with the cold-sensitive rubber tree clone ‘Reken501’. Functional analysis in yeast revealed that HbICE1 conferred cold stress resistance. Collectively, these results suggest that HbICE1 acts as a transcriptional factor and indicatively mediates the cold resistance in rubber trees.