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

The tea plant (<i>Camellia sinensis</i>) 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 (<i>Ectropis grisescens</i> Warren). Inhibition of PAL activity using 2-Aminoindan-2-phosphonic acid significantly reduced catechins accumulation and promoted larval growth of <i>E. grisescens</i>. Compared to mechanical wounding alone, simulated herbivory feeding (mechanical wounding plus oral secretions) induced higher PAL activity and more pronounced upregulation of <i>CsPAL</i> genes. This response specifically highlighted <i>CsPALb</i>, <i>CsPALd</i>, and <i>CsPALe</i> as core, herbivore-responsive members. Transient silencing of <i>CsPALb</i> in tea leaves led to a significant reduction in the levels of catechin (-)-epigallocatechin and epigallocatechin gallate. Moreover, heterologous overexpression of <i>CsPALb</i> and <i>CsPALd</i> in tobacco (<i>Nicotiana tabacum</i>) enhances resistance to <i>Spodoptera litura</i>. 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.