Abstract
NAC (NAM, ATAF1/2, and CUC2) transcription factors are ubiquitously distributed in eukaryotes and play significant roles in stress response. However, the functional verifications of NACs in Picea (P.) wilsonii remain largely uncharacterized. Here, we identified the NAC transcription factor PwNAC11 as a mediator of drought stress, which was significantly upregulated in P. wilsonii under drought and abscisic acid (ABA) treatments. Yeast two-hybrid assays showed that both the full length and C-terminal of PwNAC11 had transcriptional activation activity and PwNAC11 protein cannot form a homodimer by itself. Subcellular observation demonstrated that PwNAC11 protein was located in nucleus. The overexpression of PwNAC11 in Arabidopsis obviously improved the tolerance to drought stress but delayed flowering time under nonstress conditions. The steady-state level of antioxidant enzymes’ activities and light energy conversion efficiency were significantly increased in PwNAC11 transgenic lines under dehydration compared to wild plants. PwNAC11 transgenic lines showed hypersensitivity to ABA and PwNAC11 activated the expression of the downstream gene ERD1 by binding to ABA-responsive elements (ABREs) instead of drought-responsive elements (DREs). Genetic evidence demonstrated that PwNAC11 physically interacted with an ABA-induced protein—ABRE Binding Factor3 (ABF3)—and promoted the activation of ERD1 promoter, which implied an ABA-dependent signaling cascade controlled by PwNAC11. In addition, qRT-PCR and yeast assays showed that an ABA-independent gene—DREB2A—was also probably involved in PwNAC11-mediated drought stress response. Taken together, our results provide the evidence that PwNAC11 plays a dominant role in plants positively responding to early drought stress and ABF3 and DREB2A synergistically regulate the expression of ERD1.
Highlights
Water deficit is one of the most disruptive abiotic stresses influencing plant growth and development [1,2]
The NAC family member JUB1 was proven to be a regulator of drought stress, and the overexpression of tomato SlJUB1 or Arabidopsis AtJUB1 could increase drought tolerance in transgenic tomato by directly binding to the promoters of SlDELLA, SlDREB2 and SlDREB1 [16], suggesting that the regulation mechanisms of the NAC transcription factors involved in abiotic stress are relatively specific among different species
The results showed that the fluorescent signals for the empty vector were widely detected in the nucleus, cell membrane, and cytoplasm, but the PwNAC11-GFP fusion protein was only detected in the nucleus, indicating that PwNAC11 is a nucleus-located transcription factor (Figure 1C)
Summary
Water deficit is one of the most disruptive abiotic stresses influencing plant growth and development [1,2]. The NAC family member JUB1 was proven to be a regulator of drought stress, and the overexpression of tomato SlJUB1 or Arabidopsis AtJUB1 could increase drought tolerance in transgenic tomato by directly binding to the promoters of SlDELLA, SlDREB2 and SlDREB1 [16], suggesting that the regulation mechanisms of the NAC transcription factors involved in abiotic stress are relatively specific among different species. We found that overexpression of PwNAC11 in Arabidopsis obviously improved tolerance to drought stress by binding to the promoter of ERD1 During this process, the interaction of PwNAC11 with ABF3 synergistically activated the expression of the ERD1 promoter, resulting in increased resistance to drought stress. Our study provides the basis for a new understanding of NAC TF in genetic breeding and the improvement of coniferous forest germplasm resources
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