Comparative Microbiome Analysis of a Fusarium Wilt Suppressive Soil and a Fusarium Wilt Conducive Soil From the Châteaurenard Region.

Disease-suppressive soils are soils in which specific soil-borne plant pathogens cause only limited disease although the pathogen and susceptible host plants are both present. Suppressiveness is in most cases of microbial origin. We conducted a comparative metabarcoding analysis of the taxonomic diversity of fungal and bacterial communities from suppressive and non-suppressive (conducive) soils as regards Fusarium wilts sampled from the Châteaurenard region (France).

Transcriptome analysis of the Dickeya dadantii PecS regulon during the early stages of interaction with Arabidopsis thaliana.

PecS is one of the major global regulators controlling the virulence of Dickeya dadantii, a broad-host-range phytopathogenic bacterium causing soft rot on several plant families. To define the PecS regulon during plant colonization, we analysed the global transcriptome profiles in wild-type and pecS mutant strains during the early colonization of the leaf surfaces and in leaf tissue just before the onset of symptoms, and found that the PecS regulon consists of more than 600 genes. About one-half of these genes are down-regulated in the pecS mutant; therefore, PecS has both positive and negative regulatory roles that may be direct or indirect.

Fungal invasion of the rhizosphere microbiome.

The rhizosphere is the infection court where soil-borne pathogens establish a parasitic relationship with the plant. To infect root tissue, pathogens have to compete with members of the rhizosphere microbiome for available nutrients and microsites. In disease-suppressive soils, pathogens are strongly restricted in growth by the activities of specific rhizosphere microorganisms.

A straightforward and reliable method for bacterial in planta transcriptomics: application to the Dickeya dadantii/Arabidopsis thaliana pathosystem.

Transcriptome analysis of bacterial pathogens is a powerful approach to identify and study the expression patterns of genes during host infection. However, analysis of the early stages of bacterial virulence at the genome scale is lacking with respect to understanding of plant-pathogen interactions and diseases, especially during foliar infection. This is mainly due to both the low ratio of bacterial cells to plant material at the beginning of infection, and the high contamination by chloroplastic material.

Transgenic plants expressing the quorum quenching lactonase AttM do not significantly alter root-associated bacterial populations.

The possible impact of genetically engineered plants that degrade the quorum sensing (QS) signal of the plant pathogen Pectobacterium carotovorum was evaluated on non-target plant-associated bacterial populations and communities using Nicotiana tabacum lines expressing the lactonase AttM that degrades QS signals (AttM), and the wild type (WT) parent line. Cell densities of total culturable bacteria and those of selected populations (pseudomonads, agrobacteria) isolated from plant rhizospheres and rhizoplanes were comparable whatever the genotype of the plants (AttM or WT). Similarly, cell densities of members of the bacterial communities relying upon acyl-homoserine-lactones (AHLs) to communicate, or naturally degrading AHL signals, were identical and independent of plant genotype.

A Rhodococcus qsdA-encoded enzyme defines a novel class of large-spectrum quorum-quenching lactonases.

A gene involved in N-acyl homoserine lactone (N-AHSL) degradation was identified by screening a genomic library of Rhodococcus erythropolis strain W2. This gene, named qsdA (for quorum-sensing signal degradation), encodes an N-AHSL lactonase unrelated to the two previously characterized N-AHSL-degrading enzymes, i.e.