Phenylalanine Ammonia-Lyase as a Key Enzyme in Tea Plant Resistance to Herbivory

The tea plant (Camellia sinensis) employs inducible chemical defenses against insect herbivores, yet the role of phenylalanine ammonia-lyase (PAL) in this process remains inadequately characterized. This study demonstrates that PAL is essential for tea plant's direct resistance against the tea geometrid (Ectropis grisescens Warren). Inhibition of PAL activity using 2-Aminoindan-2-phosphonic acid significantly reduced catechins accumulation and promoted larval growth of E. grisescens. Compared to mechanical wounding alone, simulated herbivory feeding (mechanical wounding plus oral secretions) induced higher PAL activity and more pronounced upregulation of CsPAL genes. This response specifically highlighted CsPALb, CsPALd, and CsPALe as core, herbivore-responsive members. Transient silencing of CsPALb in tea leaves led to a significant reduction in the levels of catechin (-)-epigallocatechin and epigallocatechin gallate. Moreover, heterologous overexpression of CsPALb and CsPALd in tobacco (Nicotiana tabacum) enhances resistance to Spodoptera litura. Our results indicate that PAL-mediated phenylpropanoid metabolism is not only critical for herbivore resistance of tea plant, but can also provide valuable gene resources for improving herbivore resistance in other plants.