A cuticular protein mediates thermal and desiccation tolerance through dual regulation of barrier function and water homeostasis

Environmental temperature and humidity fluctuations influence insect survival and adaptation, with relevance to both contemporary pest management and future climate scenarios. The cuticle, as the primary physical barrier against environmental stress, critically determines insect adaptive capacity. Here, we investigated the role of PxPCP, a pupal cuticular protein gene, in environmental adaptation of the diamondback moth Plutella xylostella, a globally distributed pest, using CRISPR/Cas9-mediated gene editing. PxPCP knockout significantly impaired developmental performance and reproductive capacity under high temperature while reducing tolerance to temperature extremes and desiccation stress. Mutants displayed increased cuticular permeability and, unexpectedly, elevated body water content under desiccation, indicating that PxPCP regulates active water homeostasis beyond forming passive physical barriers. Transcriptional analysis revealed that PxPCP deficiency triggered compensatory upregulation of cuticle-related genes, including chitin synthase and cuticular lipid metabolism enzymes; however, these transcriptional compensations failed to fully restore cuticular barrier function. Moreover, PxPCP deletion disrupted expression of water homeostasis-related genes, including downregulation of hygroreception sensors and diuretic hormone signaling components, coupled with dysregulated ion transport and osmoprotectant biosynthesis genes, providing molecular evidence for the observed systemic water balance dysfunction. Collectively, our findings demonstrate that PxPCP plays a pivotal role in environmental adaptation by regulating cuticle formation and water homeostasis, providing a molecular basis for understanding the persistent outbreak success of this pest under climate change. These findings offer novel insights into the molecular mechanisms underlying insect climate adaptation and identify a promising molecular target for developing climate-informed pest management strategies.