*4.10. Prediction of Cis-Acting Element*

The PlantCare website (We accessed on 14 July 2021 to http://bioinformatics.psb. ugent.be/webtools/plantcare/html/) was used to predict the presence of cis-acting elements in promoter sequences (the upstream 2000 bp) of key genes of the flavonoid synthesis pathway.

#### *4.11. Statistics and Analysis*

Analysis of variance (ANOVA, *p* < 0.05), multiple comparisons (Duncan), and correlation analysis (Pearson) were performed with IBM SPSS Statistics 26.0 software (International Business Machines Corporation, New York, NY, USA), and the results are expressed as the mean ± SD. Column charts were drawn using GraphPad Prism7.0 software (GraphPad Software, LLC, San Diego, CA, USA). Principal component analysis plots were made using Origin 2019b software. Correlation heatmaps and cis-acting element visualizations were generated using TBtools v1.09876 [69].

#### **5. Conclusions**

In this study, compared with CK and NaCl treatments, spraying exogenous H2O<sup>2</sup> could promote the growth of Tartary buckwheat under NaCl stress, increase the accumulation of chlorophyll content, enhance electron transfer and transformation during photosynthesis, effectively improve enzymatic reactions, reduce cell membrane lipid peroxidation, induce or activate the expression level of related genes, alleviate the toxic effect of NaCl stress on Tartary buckwheat, and promote normal physiological metabolism and biochemical reactions in Tartary buckwheat. A concentration of 5 mmol·L <sup>−</sup><sup>1</sup> H2O<sup>2</sup> produced the optimal promoting effect on Tartary buckwheat under 150 mmol·L <sup>−</sup><sup>1</sup> NaCl stress. Appropriate concentrations of H2O<sup>2</sup> can alleviate the inhibitory effect of salt stress, but the mechanisms and signaling pathways of H2O2-mediated salt tolerance still need to be further dissected in detail, as well as how H2O<sup>2</sup> regulates related genes to activate defense systems to alleviate salt stress.

**Author Contributions:** Experimental design, X.Y., Y.P.; data analysis, X.Y., C.M., and W.W. (Weijiao Wu ); validation, X.Y., J.R., and M.Z. charting, X.Y., W.W. (Wenfeng Weng ); first draft, X.Y. and A.G.; edited and revised papers, J.R. and J.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the National Key R & D Project of China (2017YFE0117600, SQ2020YFF0402959), the National Science Foundation of China (32160669, 32161143005), and the Guizhou Science and Technology Support Program (Qiankehe Support [2020]1Y051).

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data are contained within the article.

**Acknowledgments:** We acknowledge the College of Agronomy, Guizhou University, Guiyang, China, for providing the experimental facilities and other necessary materials for this study. We are also thankful for the *Fagopyrum tataricum* breeders provided by the Alpine Crops Research Station of the Xichang Institute of Agricultural Sciences, Liangshan Prefecture, Sichuan Province, China.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

