Transcriptional responses of Pseudomonas syringae to growth in epiphytic versus apoplastic leaf sites

Significance Plant leaves are heavily colonized by microorganisms, but the extent to which the surface sites differ from interior sites in selecting for microbial colonization traits is poorly understood. Global gene-expression studies of the foliar pathogen Pseudomonas syringae reveal that leaf surface sites specifically favor active exploration using flagellar motility, chemosensing, and chemotaxis. In contrast, interior sites favor production of enzymes and secondary compounds that modulate bacterial interactions with the plant and its defense system. Water limitation is a dominating force in both surface and interior sites. These findings provide a rich understanding of the leaf habitats encountered by bacteria.