Overexpression of an SKn-dehydrin gene from Eucalyptus globulus and Eucalyptus nitens enhances tolerance to freezing stress in Arabidopsis

This work contributes in the identification and understanding of dehydrin genes and their function in the mechanisms of cold tolerance in eucalypt species. Dehydrins play a fundamental role in plant response and adaptation to abiotic stresses, having an important role in seed desiccation, response to abscisic acid, low temperatures, drought and salinity conditions. Eucalyptus nitens has a greater tolerance to cold than Eucalyptus globulus, which in part can be due to the role of dehydrins present in this species. This work reports the identification of four DHN genes in E. nitens and examines their response under low temperature, comparing them to those previously described in E. globulus. Transcript abundance of dehydrins increased when plants were cold acclimated, being higher in a freezing-resistant family of E. nitens than in a freezing-sensitive family. The relative levels of dhns in E. nitens were higher than the corresponding of E. globulus under the same conditions. The analysis of the promoter region for the four Enidhns showed that they contained several cold-or dehydration inducible cis elements, such as ABRE, MYC and CRT. The analyzes in the genomic sequence of dhn from E. globulus and E. nitens, together with the results of transcript abundance under cold acclimation, can be in part explained by differences found at the cis elements in the several DHN promoters studied. The most responsive gene to cold tolerance in both species was DHN2, which was used to obtain transgenic Arabidopsis thaliana containing either the coding region or the putative promoter. The EniDHN2 lines had higher transcript abundance than the A. thaliana with the EuglDHN2, although in both cases the transgenic lines had a higher survival rate to cold than the untransformed A. thaliana. In addition the EniDHN2 putative promoter drive induced higher expression levels of the gene (gus) marker than the one of E. globulus, when exposed to cold temperatures. Therefore, we hypothesize that the putative promoter of EniDHN2 and its coding region has a key role in conferring cold tolerance to this species.