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The biotroph Agrobacterium tumefaciens thrives in tumors by exploiting a wide spectrum of plant host metabolites
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International audience. Agrobacterium tumefaciens is a niche-constructing biotroph that exploits host plant metabolites. We combined metabolomics, transposon-sequencing (Tn-seq), transcriptomics and reverse genetics to characterize A. tumefaciens pathways involved in the exploitation of resources from the Solanum lycopersicum host plant. Metabolomics of healthy stems and plant tumors revealed the common (e.g., sucrose, glutamate) and enriched (e.g., opines, GABA, GHB, pyruvate) metabolites that A. tumefaciens could use as nutrients. Transposon-sequencing and transcriptomics pinpointed the genes that are crucial and/or up-regulated when the pathogen grew on either sucrose (pgi, kdgA, pycA, cisY) or GHB (blcAB, pckA, eno, gpsA) as a carbon source. While sucrose assimilation involved the Entner-Doudoroff and tricarboxylic acid (TCA) pathways, GHB degradation required the blc genes, tricarboxylic acid cycle and gluconeogenesis. The tumor-enriched metabolite pyruvate is at the node connecting these pathways. Using reverse genetics, we showed that the blc, pckA and pycA loci were important for aggressiveness (tumor weight), proliferation (bacterial charge) and/or fitness (competition between the constructed mutants and wild-type) of A. tumefaciens in plant tumors. This work highlighted how a biotroph mobilizes its central metabolism for exploiting a wide diversity of resources in plant host. It further shows the complementarity of functional genome-wide scans by transcriptomics and transposon-sequencing to decipher the lifestyle of a plant pathogen. This article is protected by copyright. All rights reserved.
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