Perception of Agrobacterium tumefaciens flagellin by FLS2XL confers resistance to crown gall disease.

Bacterial flagella are perceived by the innate immune systems of plants¹ and animals² alike, triggering resistance. Common to higher plants is the immunoreceptor FLAGELLIN-SENSING 2 (FLS2)³, which detects flagellin via its most conserved epitope, flg22. Agrobacterium tumefaciens, which causes crown gall disease in many crop plants, has a highly diverged flg22 epitope and evades immunodetection by plants so far studied. We asked whether, as a next step in this game of 'hide and seek', there are plant species that have evolved immunoreceptors with specificity for the camouflaged flg22^Atum of A. tumefaciens. In the wild grape species Vitis riparia, we discovered FLS2^XL, a previously unknown form of FLS2, that provides exquisite sensitivity to typical flg22 and to flg22^Atum. As exemplified by ectopic expression in tobacco, FLS2^XL can limit crown gall disease caused by A. tumefaciens.