Drought and Salinity Tolerance of the PtWRKY33 Gene in Populus

Abstract

In this study, the PtWRKY33 gene sequence was cloned by PCR from cDNA, and systematic evolutionary analysis was performed. qRT–PCR was performed to measure the expression of the PtWRKY33 gene in the roots, stems and leaves of Populus tremuloides under drought and saline stresses, and overexpression vectors were constructed and genetically transformed into tobacco. The results showed that the WRKY transcription factors of Populus trichocarpa, Populus euphratica and Populus alba were in the same branch and were closely related to each other. Treating poplar seedlings with 20% PEG6000 solution to simulate drought stress showed that expression of the PtWRKY33 gene was induced and increased 1.89 times, 3.45 times and 11.6 times in leaves, stems and roots. The relative expression of the PtWRKY33 gene was slower to respond to 150 mM NaCl treatment but was nonetheless induced. At 48 h, the increase was 1–3 times in leaves, stems and roots, respectively. NaHCO3 (60 mM) was used to treat poplar seedlings with alkaline salt stress; the results indicated that the PtWRKY33 gene was sensitive to NaHCO3 stress treatment, and that its relative expression was significantly increased and increased 10.51 times (24 h), 6.56 times (6 h) and 5.16 times (24 h) in leaves, stems and roots, respectively. In this study, we found that NaCl and NaHCO3 stress treatments were able to induce an increase in the expression of the NtSOD1 and NtAPX2 genes using qRT–PCR, and the significant increase in expression under the treatments compared with WT may be caused by overexpression of the PtWRKY33 gene. Overexpression of the PtWRKY33 gene in tobacco enhanced the antioxidant stress capacity and improved the salinity tolerance of transgenic tobacco. These results indicate that the PtWRKY33 gene is a key gene for improved salinity-tolerant growth, which is important for future molecular breeding of tree resistance.