Physiological and transcriptomic analyses of the mechanism of metformin-mediated relief in toxicity caused by saline-alkali to Akebia trifoliata

In the cultivation of Akebia trifoliata, the issue of salt-alkaline stress is frequently encountered. The objective of this work was to improve the ability of A. trifoliata to tolerate salt-alkali conditions by using external metformin. Additionally, the study attempted to understand how metformin reduces the harmful effects of salt-alkali stress in A. trifoliata by analyzing physiological and transcriptome data. Semi-annual seedlings of A. trifoliata were used as experimental materials, with three treatments: Control, SAS, and SAS + M. Morphological characteristics, biomass, photosynthetic pigments, and other indicators were measured under different treatments. Transcriptome sequencing was also conducted for comparative analysis. Under salt-alkali stress, the growth and development of A. trifoliata were severely inhibited, with down-regulation of most genes involved in photosynthesis. However, the use of metformin significantly alleviated salt-alkali damage symptoms. Plant height, stem diameter, above-ground fresh weight, above-ground dry weight, and antioxidant enzyme activities were increased. The contents of chlorophyll a, chlorophyll b, total chlorophyll, GSH, and starch increased by 47.37%, 60.63%, 49.56%, and 161.50%, respectively, while the contents of MDA and H₂O₂ decreased by 31.96% and 23.85%. RNA-seq analysis identified 8253, 5414, and 6616 DEGs in SAS vs. Control, SAS + M vs. Control, and SAS + M vs. SAS, respectively. Metformin significantly enhanced the expression of genes involved in photosynthesis, antioxidant enzymes, phenylpropanoid biosynthesis, and starch and sucrose metabolism pathways. Metformin improves salt-alkali tolerance by boosting the activity of antioxidant enzymes, raising the levels of GSH and starch, and up-regulating the expression of genes involved in photosynthesis, antioxidant enzymes, phenylpropanoid biosynthesis, starch, and sucrose metabolism pathways.