Managing water on plant leaf surfaces: Roles and regulation of hydrophobicity

Hydrophobicity-the ability of plant surfaces to repel water-is a fundamental physical property that governs interactions between plants and their environment. It plays vital roles in pathogen defense, photosynthetic efficiency, and water balance. Although long recognized as a defining feature of terrestrial plants, the mechanisms underlying the formation and regulation of surface hydrophobicity has just recently begun to be elucidated at structural and genetic levels. This review integrates current understanding of the biological significance of hydrophobicity in maintaining plant fitness, the hierarchical surface architectures such as epidermal roughness and epicuticular wax crystals that determine hydrophobicity, and the molecular genetic pathways that control these structures. Special attention is given to rice and lotus, which exemplify superhydrophobic leaf surfaces and serve as valuable structural and genetic models. We highlight how coordinated regulation of epidermal morphogenesis and wax biosynthesis establishes hydrophobicity, and how its natural variation reflects adaptive optimization to ecological conditions. A mechanistic understanding of these processes not only clarifies the evolutionary strategies of plants but also provides a conceptual and practical foundation for engineering leaf surface wettability to improve crop resilience and sustainable agricultural performance.