Toward a plant biotechnological application of phyllosphere bacteria.

The phyllosphere, referring to the leaf-dominated aerial parts of plants, represents a vast yet challenging habitat for plant-associated bacteria. A growing body of evidence indicates that phyllosphere bacteria provide host plants with a variety of beneficial effects, including growth promotion, enhanced stress tolerance, and pathogen resistance, garnering significant attention for their potential in biotechnological applications. However, our understanding of the molecular mechanisms underlying these bacterial functions in plant growth and health remains limited. Enhancing the beneficial effects of phyllosphere bacteria requires a deeper understanding of how they adapt to the harsh leaf environment, characterized by limited and unstable water and nutrient availability as well as host-induced defense responses. Moreover, recent studies are beginning to unravel the complex interplay among host plants and members of leaf bacterial communities, which serves as a key driver of the emergence of bacterial functions in the phyllosphere. In this review, we synthesize both early and recent advancements in our understanding of bacterial functions and adaptations in the phyllosphere at the levels of individual strains and communities and propose future research directions to harness phyllosphere bacteria for plant biotechnological applications.