Transcriptomic and metabolomic insights into the adaptive response of Salix viminalis to phenanthrene

Polycyclic aromatic hydrocarbons (PAHs) are widespread, persistent environmental pollutants. They exert toxic effects at different developmental stages of plants. Plant defense mechanisms against PAHs are poorly understood. To this end, transcriptomics and widely targeted metabolomic sequencing were used to study the changes in gene expression and metabolites that occur in the roots of Salix viminalis subjected to phenanthrene stress. Significant variations in genes and metabolites were observed between treatment groups and the control group. Thirteen amino acids and key genes involved in their biosynthesis were upregulated exposed to phenanthrene. Cysteine biosynthesis was upregulated. Sucrose, inositol galactoside, and mellidiose were the main carbohydrates that were largely accumulated. Glutathione biosynthesis was enhanced in order to scavenge reactive oxygen species and detoxify the phenanthrene. Glucosinolate and flavonoid biosynthesis were upregulated. The production of pinocembrin, apigenin, and epigallocatechin increased, which may play a role in antioxidation to resist phenanthrene stress. In addition, levels of six amino acids and N,N'-(p-coumaroyl)-cinnamoyl-caffeoyl-spermidine were significantly increased, which may have helped protect the plant against phenanthrene stress. These results demonstrated that S. viminalis had a positive defense strategy in response to phenanthrene challenge. Subsequent defense-related reactions may have also occurred within 24 h of phenanthrene exposure. The findings of the present study would be useful in elucidating the molecular mechanisms regulating plant responses to PAH challenges and would help guide crop and plant breeders in enhancing PAH resistance.