CsAFS1 Enhances the Self-Resistance of Tea Plants by Promoting Terpenoid Accumulation

The intercropping of tea plants with Chinese chestnut has been recognized as an advanced and eco-friendly cultivation method that enhances the self-resistance of tea plants. This study aimed to investigate the relationship between plant hormones and CsAFS1 based on previous findings and to reveal the mechanism by which CsAFS1 enhances the resistance of tea plants intercropped with Chinese chestnut. In this study, an α-farnesene synthase (AFS) was identified in tea plants intercropped with Chinese chestnut through transcriptome sequencing. This gene was actively expressed during cold and under exogenous methyl jasmonate (MeJA), salicylic acid (SA), abscisic acid (ABA), and gibberellic acid (GA) induction. The gene was cloned, and the bioinformatics analysis revealed that its encoded protein was clustered within the same evolutionary branch as camellia proteins, and hence it was named CsAFS1. The promoter analysis revealed multiple cis-acting elements responsive to cold, JA, MeJA, and SA. After transformation of CsAFS1 into tobacco plants, the transgenic tobacco plants exhibited growth similar to that of wild-type tobacco plants, but with longer and denser glandular trichomes. Aphid and cold stress were used as representative examples of biotic and abiotic stresses in transgenic tobacco plants, respectively. Enhanced resistance to aphid and cold stress was associated with increased levels of osmoregulatory substances and protective enzyme activities, upregulated expression of stress-related genes, and reduced reactive oxygen species production. CsAFS1 was also found to respond rapidly to MeJA and SA, and significant changes in terpenoid content, for example, nerolidol, were observed. These findings suggested that CsAFS1 enhanced stress resistance by boosting antioxidant enzyme activity, the level of osmoregulatory substances, and secondary metabolites, hormone signaling, and systemic acquired resistance, making tea plants or tea plantations much healthier. This study provided a theoretical foundation for understanding stress regulation in tea plants and for breeding stress-resistant varieties.