Functional characterization of Zoysia japonica ZjNAC3 gene in response to salt stress

Salt stress can accelerate the rate of yellowing and affect the overall value of turfgrass. Although NAC transcription factors have been reported to play important roles in plant salt tolerance, only a few studies have described the functional characterization of NAC genes in Zoysia japonica. In this study, we used yeast strain YPH500 transformed with the ZjNAC3 gene to evaluate the contribution of this gene to salt stress tolerance. Our preliminary data determined that ZjNAC3 negatively regulates yeast cell growth during salt stress with this being further confirmed in a transgenic Arabidopsis thaliana treated with salt. Our analysis showed that the growth of these transgenic plants was significantly weaker than wild-type (WT) plants after 7 days of treatment with 150 mmol·L⁻¹ NaCl. Proline, MDA content, and cell membrane permeability were also all significantly higher in ZjNAC3−overexpressing lines than in WT (P < 0.05), whereas chlorophyll and soluble sugar content was decreased in transgenic plants (P < 0.05). In addition, the expression of AtNHX1 in the transgenic lines was significantly lower than that in WT plants (P < 0.05). Taken together, these data indicate that the overexpression of the ZjNAC3 gene decreases salt tolerance in Arabidopsis plants. It is thus rational to deduce that the decline in osmotic regulation, severe cell damage, and weakened ability to isolate Na⁺ into vacuoles all contribute to the salt-sensitive phenotype of these transgenic Arabidopsis plants. This study revealed that ZjNAC3 is an important gene regulating salt stress tolerance and lays the foundation for the future exploration of NAC transcription factors in Zoysia japonica.