Beneath the Bark: Molecular Determinants of Adaptation and Infection in Bacterial Pathogens of Woody Hosts.

Bacterial pathogens of woody plants represent a pervasive yet underexplored threat to global agriculture and forestry, causing devastating diseases in fruit trees, shrubs, forest trees and ornamental species. Unlike pathogens of herbaceous plants, the molecular strategies enabling bacteria to colonise and damage woody tissues remain poorly understood, owing to the experimental challenges associated with woody host systems and the distinctive biology of these plants. Moreover, persistence within long-lived woody tissues requires prolonged modulation of host immune signalling, enabling pathogens to evade or attenuate defence responses across growing seasons. This review synthesises current knowledge of the virulence mechanisms underlying bacterial infection of woody hosts, highlighting host-specific strategies and conserved pathways critical for disease establishment. Key mechanisms include manipulation of plant immune responses through type III secretion system effectors and other secreted proteins, catabolism of host-derived metabolites, degradation of structural barriers, and the activity of bacterial toxins and extracellular polysaccharides. By integrating these molecular insights, we examine how bacterial pathogens have evolved adaptive strategies to overcome the unique challenges posed by woody tissues and emphasise the implications for disease management in economically important crops. Addressing knowledge gaps in woody-host infections is essential for developing innovative, targeted strategies to mitigate the impact of these pathogens and safeguard global woody crops and forestry systems.