Tracing Xanthomonas translucens evolution reveals gene loss for broad host range emergence

Notably, deletion of the previously uncharacterized effector gene xopAL1 promoted host expansion to wheat but reduced fitness in barley, supporting a fitness tradeoff for niche expansion. Furthermore, transcriptomic analysis revealed specific XopAL1-dependent defense response components of wheat. Three candidate defense response genes were identified and validated for their functional role in defense against X. translucens via individual targeted gene induction using artificial transcription activator-like effectors (arTALEs).

Conversely, we identified that the barley specialist lineage Xtt gained the effector gene xopAJ, which limits disease development in oat but may contribute to barley adaptation. This research provides an experimentally validated evolutionary framework for predicting pathogen emergence based on gene loss, and host adaptation via gene gain, and identifies key host defense components for durable disease control.