How bacteria subvert plant immunity

Early detection of the enemy is a central tenet of an immune system’s fight against microbial pathogens. For this purpose, plants and animals have evolved dedicated receptors to detect pathogen-associated molecular patterns (PAMPs) that trigger a host of defense responses (1). These ancient and conserved surveillance systems detect equally conserved PAMPs, which have diverse chemical structures, including bacterial flagellin and lipopolysaccharides. The ability of plants and animals to recognize such microbial signatures has driven the evolution of sophisticated countermeasures by pathogens to evade detection. On page 297 of this issue, Sanguankiattichai et al. (2) report that pathogenic bacteria undermine plant perception of flagellin by producing an iminosugar, called glycosyrin, that inhibits a plant glycosidase required for flagellin detection and thereby suppresses plant immune responses. The finding has broad implications for the role of glycobiology in plant-microbe interactions and also drug discovery.