Project description:Epidemic preparedness depends on tracking microbial evolution that drives disease emergence. For outbreaks caused by host jump, we often identify the causal agent, but functional validation of pathogen emergence lags behind. Here, we defined the role of effector gene loss in the emergence of a generalist lineage of Xanthomonas translucens, an important bacterial plant pathogen of cereals and grasses. This lineage, X. translucens pv. undulosa, causes disease in multiple genera of cereals and grasses and encodes significantly fewer virulence effector genes than the specialist sister lineage X. translucens pv. translucens, which infects barley only. Genomic analyses suggested events contributing to host expansion, and we experimentally reproduced effector gene loss evolution by deleting the effectors unique to the specialist lineage. 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.
Project description:This study aimed at decrypting the transcriptomic response of 2 months-old grown tender wheat (cv Chinese Spring) to a the Xanthomonas translucens pathogen infection by infiltration. The response was monitored by RNAseq 24h post leaf clipping. Triticum aestivum cv. Chinese Spring plants were maintained in a growth chamber with cycles of 12 h of light at 21C and 50% relative humidity (RH) and 12 h of dark at 21C and 50% RH. Leaves of 49 days-old plants were infiltrated with a bacterial suspension in water with an optical density at 600 nm (OD600) of 0.5 using a needleless syringe. Plants inoculated with water were used as controls. For transcriptomic and proteomic analyses, leaves and root tissues were harvested 1 day post-inoculation (dpi), when symptoms were not visible yet. Three biological replicates per treatment were performed, and each with pooled leaves from two independent plants per replicate. The files per conditions and replicates are:Sample 1 Root tissue with 3 replicates: CONTROL * control condition for roots (wheat without pathogen infection): 3 replicates: 1.1R,1.2R, 1.3R * control condition for leaves (wheat without pathogen infection): 3 replicates1.1L,1.2L, 1.3L * Wheat Roots infected by Xanthomonas translucens: 3 replicates: 5.1R, 5.2R, 5.3R * Wheat Leaves infected by Xanthomonas translucens: 3 replicates: 5.1L, 5.2L, 5.3L
