Physiological and Transcriptomic Characterization of Salt-Stress Responses in the Pyrethrin-Producing Ornamental Plant Tanacetum coccineum

Tanacetum coccineum is an ornamental plant capable of producing pyrethrins, natural insecticidal metabolites. Salinity restricts plant growth, but its effects on stress responses and pyrethrin-related metabolism remain poorly understood in this species. In this study, seedlings were treated with 0, 100, or 200 mM NaCl for 7 days, followed by physiological measurements and transcriptome analysis of leaf and root. Salt stress caused progressively more severe leaf injury and distinct antioxidant responses in the two tissues. Transcriptome analysis revealed extensive tissue-dependent transcriptional changes, including differential expression of genes associated with antioxidant defense, ABA biosynthesis, and pyrethrin metabolism. Several pyrethrin biosynthesis-related genes were upregulated under moderate salinity, whereas their expression patterns became more variable at higher NaCl concentrations. Meanwhile, spectrophotometrically estimated leaf pyrethrin content increased with NaCl concentration. WGCNA and PPI network analyses identified candidate hub genes associated with ion homeostasis, oxidative defense and carbon metabolism. Further analysis identified 19 candidate transcription factors and significant co-expression associations with ABA- and pyrethrin-related genes, suggesting potential transcriptional links between salt-stress responses and specialized metabolism. Collectively, these findings reveal tissue-dependent responses to salinity and provide insights into the transcriptional complexity of pyrethrin-related metabolism in T. coccineum.