Abstract
Longan (Dimocarpus longan) is a typical southern subtropical fruit tree species that is sensitive to cold stress. C-repeat binding factors (CBFs), as transcription factors, are crucial components involved in the molecular regulation of the plant response to cold stress. However, the role of CBF homologs in the cold response regulation of longan remains largely unknown. Here, three novel CBF genes, DlCBF1, DlCBF2, and DlCBF3, were cloned from longan. DlCBF1 and DlCBF2 contain an AP2 domain and PKKPAGR and DSAWR CBF signature motifs, while DlCBF3 has mutations within these conserved signature motifs. DlCBF1/2/3 were mainly localized in the nucleus and specifically bound to CRT/DRE cis-elements, resulting in strong transcriptional activation. DlCBF1/2 exhibited tissue expression specificity, and their expression was induced by low temperature, while DlCBF3 had no tissue specificity and barely responded to low temperature. DlCBF1, DlCBF2, and DlCBF3 overexpression in Arabidopsis-enhanced cold tolerance by increasing proline accumulation and reducing reactive oxygen species (ROS) content, accompanied by upregulated expression of cold-responsive genes (AtRD29A, AtCOR15A, AtCOR47, and AtKIN1) in the CBF cold stress response signaling pathway. In conclusion, the biological functions of DlCBF1/2/3 were somewhat conserved, but slow expression of DlCBF1/2 and low expression of DlCBF3 may partly cause the cold sensitivity of longan. Collectively, these results indicated that differences exist in the expression and function of CBF orthologs in the cold-sensitive plant species longan, and these findings may help to improve the understanding of the cold response regulation mechanism and provide important theoretical support for cold-tolerant breeding of longan.
Highlights
Cold stress is an adverse abiotic factor that restricts the geographical distribution of plants and influences crop growth and development, resulting in decreased productivity and quality of many important crop species (Pearce, 2001)
The results revealed that the biological functions of DlCBF1/2/3 in the longan response to cold stress are conserved to some extent but that the expression was insufficient, especially for DlCBF3, which might partly result in longan cold sensitivity
The expression of DlCBF3 was consistently low, and the expression trend did not change significantly (Figure 2C). These results suggested that the expression modes of the three C-repeat binding factors (CBFs) were different and that the gene expression of DlCBF1/2 was induced by a cold signal in longan, whereas that of DlCBF3 was not
Summary
Cold stress is an adverse abiotic factor that restricts the geographical distribution of plants and influences crop growth and development, resulting in decreased productivity and quality of many important crop species (Pearce, 2001). Accumulating evidence has revealed that C-repeat binding factor (CBF) transcription factors (TFs) play important roles in the stress response and in plant growth and development. Cold-induced CBF genes recognize and bind to the conserved C-repeat/ dehydration response motif (CRT/DRE, CCGAC), which is present in the promoters of genes, thereby inducing the expression of cold-regulated (COR) genes (Stockinger et al, 1997; Medina et al, 2011). COR genes encode cryoprotective proteins and some key enzymes involved in the accumulation of metabolites (osmolytes) that enhance the cold tolerance of plants (Ding et al, 2019)
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