Altered DREB1A Gene Expression in Arabidopsis thaliana affects Root Growth, Antioxidant Enzymes Activity, and Response to Salinity but Not to Cold

DREB1A (Dehydration Responsive Element Binding 1A) transcription factor is involved in plant responses to abiotic stresses. An A. thaliana DREB1A T-DNA insertional mutant (dreb1a) alongside previously reported DREB1A over-expressing plants (OX28) were detailed in molecular and phenotypic characterizations. The T-DNA of the dreb1a line was inserted at position -253, and segregation ratio confirmed a single T-DNA locus in its T0 plant population. The RT-PCR analysis of dreb1a seedlings also revealed a null mutant in the DREB1A gene. The phenotypes of the dreb1a seedlings subjected to cold stress were not different from those of the wild type (WT-Col0), but under salinity dreb1a plants showed about 11% less seed germination and the four times less survival rate, compared to WT-Col0 plants. Under normal growth conditions, there was a direct correlation between DREB1A expression levels and the root length as the dreb1a, in contrast to the OX28 line, showing 29% longer roots than that in the WT-Col0 plants. Interestingly, this root phenotype had an association with the accumulation of reactive oxygen species (ROS) in dreb1a by 31% less, and in OX28 by 97% more than that in the control seedlings. In addition, the dreb1a plant possessed significantly higher activities in superoxide dismutase, peroxidase, polyphenol oxidase and significantly lower activity in catalase than WT-Col0, but no differences in extracellular peroxidase activity. On the other hand, the OX28 plant possessed a higher extracellular peroxidase activity. Overall, these results suggest that a precise expression level of DREB1A gene is required for proper growth and development in A. thaliana.