Bioinformatic prediction of the AP2/ERF family genes in Eucalyptus grandis: focus on the CBF family

Background Due to their very high economic importance, Eucalyptus tree species are among the most planted hardwoods in the world with over 20 million hectares. However, as long-lived evergreen species, this genus is particularly exposed to cold. Frost tolerance varies among species and is inversely correlated to productivity. The AP2/ERF gene family includes developmentally and physiologically important transcription factors characterized by the presence of the AP2/ERF DNA-binding domain. AP2 proteins contain two AP2-like domains and RAV family proteins contain one AP2 domain and one B3 domain. ERF family proteins exhibit only one AP2 domain and are further divided into the DREB subfamily and the ERF subfamily [1]. The CBF/DREB1 protein differ from the other DREB proteins by the presence of “signature sequences” (PKK/RPAGRxKFxETRHP and DSAWR) flanking the DNA-binding AP2 domain [2]. The DREB factors recognize the C-repeat or dehydration response element (DRE) in the promoters of low temperature and/or water deficit responsive genes and would play a crucial role in response to abiotic stresses. CBF/DREB1 are the key regulators of the cold-responsive (COR) genes. So far CBF transcription factors have been mainly characterized in model plants such as Arabidopsis, but lately they were identified in several tree species including Eucalyptus [2]. The Eucalyptus cold tolerance was greatly improved in our hands when two genes from the four CBF members isolated from a tolerant species E. gunnii were individually constitutively overexpressed in the frost sensitive E. urophylla x E. grandis hybrid [3]. In the present study E. grandis AP2/ERF family genes were identified based on the presence of putative encoding AP2-domain(s) and were studied with regard to the model herbaceous Arabidopsis as well as the main sequenced woody plants. Within this family, a part of the study focused on the CBF/DREB1 subfamily which was compared to the four genes already characterized in E. gunnii[2].