A novel CBF that regulates abiotic stress response and the ripening process in oil palm (Elaeis guineensis) fruits

A new member of the C-repeat binding factor (CBF) encoding an AP2-domain protein was isolated from ripening oil palm (Elaeis guineensis var. DuraxPisifera) fruit. Bioinformatics analysis revealed that EgCBF3 has an AP2 DNA binding domain containing 57 amino acids. According to the signature sequences found upstream and downstream of the AP2 domain, it was predicted that the deduced amino acid sequence belongs to the A-1 group of the CBF/DREB1 subfamily. EgCBF3 is differentially expressed in the fruit mesocarp tissue with the highest transcript accumulation in ripening fruit at 17 weeks after anthesis (w.a.a.). In the vegetative tissues, it showed higher expression levels in the roots compared to the leaves. In the mesocarp tissue, expression of EgCBF3 was upregulated after 2 h and peaked after 24 h of cold, ethylene and ABA treatments, while for drought and salt stresses, it exhibited the highest expression after 4 and 8 h, respectively. GFP fusion protein of EgCBF3 was localized to the nucleus of the onion's epidermal cells. The in vitro and in vivo DNA-protein transactivation assay using electrophoretic mobility shift assay (EMSA) and yeast one-hybrid analysis revealed that EgCBF3 was able to bind to the DRE/CRT cis-element. Tomato was chosen as a model system for the climacteric oil palm fruits. Expression profile of the ethylene and abscisic acid biosynthesis-related genes and ripening-related genes were affected by transient overexpression of EgCBF3 in the tomato fruits at different developmental stages. These results suggest that EgCBF3 can mediate abiotic stress response in ripening fruits and may function as a regulator of ripening process-related genes.