Functional characterization and expression profiling of a DREB2-type gene from lettuce (Lactuca sativa L.)

Abstract

Dehydration responsive element binding factors (DREBs) play important roles in plant responses to abiotic stress. In this study, a DREB2-type gene, LsDREB2A, was isolated from lettuce (Lactuca sativa L.) and characterized. LsDREB2A encoded a protein of 322 amino acid residues with the conserved apetala 2 domain and was classified into the A2 subgroup of DREBs. LsDREB2A has no sequence rich in proline, glutamic acid, serine, and threonine to trigger protein degradation. Southern blot analysis indicated that there could be more than ten DREB homologs in lettuce. A gel shift assay indicated that LsDREB2A could specifically recognize the dehydration responsive element (DRE) sequence in vitro. In a yeast one-hybrid assay, LsDREB2A bound specifically to the DRE sequence and activated the expression of both His3 and LacZ reporter genes. A transient expression experiment in lettuce protoplasts showed that LsDREB2A was localized to the nucleus. These results suggest that LsDREB2A might function as a transcription factor. Quantitative real-time polymerase chain reaction revealed that the expression of LsDREB2A was significantly increased by hyperosmotic and high salinity treatment, but not cold, heat, nor abscisic acid (ABA) treatment. Overexpression of LsDREB2A increased the tolerance of salt stress in transgenic plants. These results suggested that LsDREB2A plays an important role during high salinity stress in an ABA-independent pathway.