Abstract
ICE (inducer of CBF expression) is a positive regulator of cold signaling pathway in plants. Identification of ICE transcription factors is important for the sustainable development of the natural rubber planting industry in nontraditional regions where sudden cold waves often occur. In this study, five ICE genes were isolated from genome of rubber tree (Hevea brasiliensis Muell. Arg.) for analysing tolerance to cold stress. They shared an ICE-specific region in the highly conserved bHLH-ZIP domain and were localized in the nucleus. The HbICEs were different in transcript abundance and expression patterns in response to cold and drought stresses and among different rubber tree clones. Generally, the expression level of HbICEs was significantly higher in the cold-tolerant rubber tree clones than that in the cold-sensitive rubber tree clones. Overexpression of HbICE1, HbICE2, and HbICE4 significantly enhanced the cold tolerance of transgenic Arabidopsis and tobacco, which showed a significant increase in chlorophyll content and decrease in relative water content and conductivity at the early stage of cold stress in comparison with wild-type plants. Furthermore, overexpression of HbICE2 and HbICE4, but also HbICE1 enhanced drought tolerance in transgenic Arabidopsis. The cold tolerance of rubber tree clones is positively controlled by the expression level of HbICE1, HbICE2, and HbICE4.
Highlights
Plants have evolved efficient and sophisticated mechanisms involving altered physiological and biochemical processes to adapt to cold and drought stress
The full-length cDNAs of HbICE genes were cloned from rubber tree 93-114 and their names were shown on the basis of the phylogenetic relationship between rubber tree and other plant species
The coding sequences of HbICE genes exhibited the range of 1011 bp (HbICE5) to 1617 bp (HbICE1), the encoded proteins ranged from 336 to 538 amino acid residues, with corresponding molecular masses of 37.89–59.00 kDa, with the predicted isoelectric points of 4.75 (HbICE5) to 5.86 (HbICE2)
Summary
Plants have evolved efficient and sophisticated mechanisms involving altered physiological and biochemical processes to adapt to cold and drought stress. These changed physiological and biochemical processes are involved in changes of gene expression profiles. Inducer of CBF expressions (ICEs) are MYC-like basic helix-loop-helix (bHLH) transcription factors regulating plant responses to cold and drought stress. They contain some very similar motifs, such as acidic domain, Ser-rich domain, bHLH domain, zipper region, and dimerization domain [1,2,3]. ZjICE1 in Zoysia japonica, PtrICE1 in trifoliate orange, and ICEs (TaICE1a and TaICE1d) in wheat are induced by drought and cold treatment [7,8,9]
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