An Isolate of <i>Xanthomonas hortorum</i> pv. <i>vitians</i> for the Study of Asteraceae Immune Responses

The AvrRps4 effector family is characterized by homology with the bipartite bacterial effector AvrRps4. The known members of this family (HopK1, XopO, and AvrRps4) are processed into two moieties within the plant cell. Previous research has shown that Lactuca sativa (lettuce) cultivars are variously capable of recognizing the N-terminal fragment of processed AvrRps4 (AvrRps4 N ) with or without the C terminus (AvrRps4 C ) when transiently expressed by Agrobacterium tumefaciens but are incapable of recognizing AvrRps4 C . To investigate this relationship in a natural pathosystem, we isolated and characterized a strain of Xanthomonas hortorum pv. vitians from leaves of L. serriola and used it to deliver the AvrRps4 homolog XopO by natural effector delivery. We also show that this strain can be used to investigate plant–pathogen interactions in plants beyond lettuce. [Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .