A luminescent reporter evidences active expression of Ralstonia solanacearum type III secretion system genes throughout plant infection
Monteiro, Freddy | Genin, Stéphane | van Dijk, Irene | Valls, Marc | Dept Genet, ; Universitat de Barcelona (UB) | Institut de Recerca i Tecnologia Agroalimentàries = Institute of Agrifood Research and Technology (IRTA) | Unité mixte de recherche interactions plantes-microorganismes ; Institut National de la Recherche Agronomique (INRA)-Université Toulouse III - Paul Sabatier (UT3) ; Université de Toulouse (UT)-Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS) | Fundacao para a Ciencia e a Tecnologia [RFRH/BD/45850/2008]; Comissionat per Universitats i Recerca of the Generalitat de Catalunya [SGR0052, CONES2010-0030]; Ministerio de Ciencia, Tecnologia e Innovacion of the Spanish Government [HF2008-0021, AGL2010-21870]; [ANR-10-LABX-41]
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Показать больше [+] Меньше [-]Английский. Although much is known about the signals that trigger transcription of virulence genes in plant pathogens, their prevalence and timing during infection are still unknown. In this work, we address these questions by analysing expression of the main pathogenicity determinants in the bacterial pathogen Ralstonia solanacearum. We set up a quantitative, non-invasive luminescent reporter to monitor in planta transcription from single promoters in the bacterial chromosome. We show that the new reporter provides a real-time measure of promoter output in vivo - either after re-isolation of pathogens from infected plants or directly in situ - and confirm that the promoter controlling exopolysaccharide (EPS) synthesis is active in bacteria growing in the xylem. We also provide evidence that hrpB, the master regulator of type Ill secretion system (T3SS) genes, is transcribed in symptomatic plants. Quantitative RT-PCR assays demonstrate that hrpB and type HI effector transcripts are abundant at late stages of plant infection, suggesting that their function is required throughout disease. Our results challenge the widespread view in R. solanacearum pathogenicity that the T3SS, and thus injection of effector proteins, is only active to manipulate plant defences at the first stages of infection, and that its expression is turned down when bacteria reach high cell densities and EPS synthesis starts.
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