Constitutive expression of two A-5 subgroup DREB transcription factors from desert shrub Ammopiptanthus mongolicus confers different stress tolerances in transgenic Arabidopsis

Dehydration-responsive element binding proteins (DREBs) constitute a large subfamily in the plant-specific APETALA2/ethylene-responsive factor (ERF) family and play crucial roles in plant stress tolerance. So far, studies on the A-5 subgroup DREBs which comprise the largest proportion of the DREB subfamily are limited. Here, we report functional characterization of two A-5 subgroup genes named AmDREB1 and AmDREB2 from Ammopiptanthus mongolicus, a desert shrub with high abiotic stress tolerance. Both AmDREB1 and AmDREB2 proteins contain an ERF-associated amphiphilic repression (EAR)-like motif and were localized in the nucleus. The transcription levels of AmDREB1 and AmDREB2 in laboratory-cultured seedlings increased differentially under dehydration, salt, cold and/or heat stresses as well as under abscisic acid (ABA) treatment. In leaves of naturally growing shrubs in the wild, the transcription level of AmDREB2 also increased in response to seasonal cold weather of a year. Moreover, AmDREB1 was most abundantly expressed in leaves, followed by immature pods; AmDREB2 was abundantly expressed in all examined organs. Constitutively expressing AmDREB1 in Arabidopsis significantly enhanced drought and salt tolerances of transgenic lines, likely by inducing the expression of some stress-inducible genes and accumulating more proline and less Na+. Constitutive expression of AmDREB2 conferred only osmotic stress tolerance in transgenic Arabidopsis at the seed germination stage. Both AmDREBs also conferred ABA insensitivity in transgenics. This study provides important evidence that the A-5 subgroup EAR motif-containing DREBs can positively regulate stress response and tolerance in plants, and that AmDREB1 may have potential application in improving drought and salt tolerances in crop plants. AmDREB1 and AmDREB2 were differentially induced by abiotic stressors, exogenous ABA and seasonal cold weather. The tolerances of their transgenics to drought and/or salt as well as ABA were enhanced.