Denance, N. | bioRxiv Science

bioRxiv2022

Two bridgehead invasions of Xylella fastidiosa subsp. multiplex in France

Of American origin, a wide diversity of Xylella fastidiosa strains belonging to different subspecies have been reported in Europe since 2013 and its discovery in Italian olive groves. Strains from the subspecies multiplex (ST6 and ST7) were first identified in France in 2015 in urban and natural areas. To trace back the most probable scenario of introduction in France, the molecular evolution rate of this subspecies was estimated at 3.2165 x 10-7 substitutions per site per year, based on heterochronous genome sequences collected worldwide. This rate allowed the dating of the divergence between French and American strains in 1987 for ST6 and in 1971 for ST7. The development of a new VNTR-13 scheme allowed tracing the spread of the bacterium in France, hypothesizing an American origin. Our results suggest that both sequence types were initially introduced and spread in Provence-Alpes-Cote dAzur (PACA); then they were introduced in Corsica in two waves from the PACA bridgehead populations.

microbiology↗

bioRxiv2020

Arabidopsis cell wall composition determines disease resistance specificity and fitness

Plant cell walls are complex structures subject to dynamic remodeling in response to developmental and environmental cues, and play essential functions in disease resistance responses. We tested the specific contribution of plant cell walls to immunity by determining the susceptibility of a set of Arabidopsis cell wall mutants (cwm) to pathogens with different parasitic styles: a vascular bacterium, a necrotrophic fungus and a biotrophic oomycete. Remarkably, most cwm mutants tested (31/38; 81.6%) showed alterations in their resistance responses to at least one of these pathogens, in comparison to wild-type plants, illustrating the relevance of wall composition in determining disease resistance phenotypes. We found that the enhanced resistance of cwm plants to the necrotrophic and vascular pathogens negatively impacted on cwm fitness traits, like biomass and seed yield. Enhanced resistance of cwm plants is not only mediated by canonical immune pathways, like those modulated by phytohormones or Microbe-Associated Molecular Patterns, which are not de-regulated in all cwm tested. Pectin-enriched wall fractions isolated from cwm plants triggered immune responses in other plants, suggesting that wall-mediated defensive pathways might contribute to cwm resistance. Cell walls of cwm plants show a high diversity of composition alterations as revealed by glycome profiling that detect specific wall carbohydrate moieties. Mathematical analysis of glycome profiling data identified correlations between the amounts of specific wall carbohydrate moieties and disease resistance phenotypes of cwm plants. These data support the relevant and specific function of plant wall composition in plant immune response modulation and in balancing disease resistance/development trade-offs.

plant biology↗