Biology subjects

Navaud, O.

Publications and source records attributed to Navaud, O..

4 recordsLinked to original sources

bioRxiv2020

Transcriptional response to host chemical cues underpins expansion of host range in a fungal plant pathogen lineage

The host range of parasites is an important factor in assessing the dynamics of disease epidemics. The evolution of pathogens to accommodate new hosts may lead to host range expansion, a process the molecular bases of which are largely enigmatic. The fungus Sclerotinia sclerotiorum parasitizes more than 400 plant species from diverse eudicot families while its close relative, S. trifoliorum, is restricted to plants from the Fabaceae family. We analyzed S. sclerotiorum global transcriptome reprogramming on hosts from six botanical families and reveal a flexible, host-specific transcriptional program driven by core and host-response co-expression (SPREx) gene clusters. We generated a chromosome-level genome assembly for S. trifoliorum and found near-complete gene space conservation in broad and narrow host range Sclerotinia species. However, S. trifoliorum showed increased sensitivity to the Brassicaceae defense compound camalexin. Inter-specific transcriptome analyses revealed a lack of transcriptional response to camalexin in S. trifoliorum and provide evidence that cis-regulatory variation associates with the genetic accommodation of Brassicaceae in the Sclerotinia host range. Our work demonstrates adaptive plasticity of a broad host range pathogen with specific responses to different host plants and demonstrates the co-existence of signatures for generalist and polyspecialist life styles in the genome of a plant pathogen. We reason that this mechanism enables the emergence of new disease with no or limited gene flow between strains and species, and could underlie the emergence of new epidemics originating from wild plants in agricultural settings.

genomics↗

bioRxiv2018

Rapid identification of an Arabidopsis NLR gene conferring susceptibility to Sclerotinia sclerotiorum using time-resolved automated phenotyping

The broad host range necrotrophic fungus Sclerotinia sclerotiorum is a devastating pathogen of many oil and vegetable crops. Plant genes conferring complete resistance against S. sclerotiorum have not been reported. Instead, plant populations challenged by S. sclerotiorum exhibit a continuum of partial resistance designated as quantitative disease resistance (QDR). Because of their complex interplay and their small phenotypic effect, the functional characterization of QDR genes remains limited. How broad host range necrotrophic fungi manipulate plant programmed cell death is for instance largely unknown. Here, we designed a time-resolved automated disease phenotyping pipeline and assessed the kinetics of disease symptoms caused by seven S. sclerotiorum isolates on six A. thaliana natural accessions with unprecedented resolution. We hypothesized that large effect polymorphisms common to the most resistant A. thaliana accessions, but absent from the most susceptible ones, would point towards disease susceptibility genes. This identified highly divergent alleles of the nucleotide-binding site leucine-rich repeat gene LAZ5 in the resistant accessions Rubenzhnoe and Lip-0. Two LAZ5-deficient mutant lines in the Col-0 genetic background showed enhanced QDR to S. sclerotiorum, whereas plants mutated in the closely related CSA1 gene responded like the wild type. These findings illustrate the value of time-resolved image-based phenotyping for unravelling the genetic bases of complex traits such as QDR. Our results suggest that S. sclerotiorum manipulates plant sphingolipid pathways guarded by LAZ5 to trigger programmed cell death and cause disease.

plant biology↗

bioRxiv2018

Small RNAs from the plant pathogenic fungus Sclerotinia sclerotiorum highlight candidate host target genes associated with quantitative disease resistance

Plant pathogenic fungi secrete effector proteins and secondary metabolites to cause disease. Additionally, some produce small RNAs (sRNAs) that silence transcripts of host immunity genes through RNA interference. The fungus Sclerotinia sclerotiorum infects over 600 plant species, but little is known about its molecular interactions with its hosts. In particular, the role of sRNAs in S. sclerotiorum pathogenicity has not been determined. By sequencing sRNAs in vitro and during infection of two host species, we found that S. sclerotiorum produces at least 374 highly abundant sRNAs. These sRNAs mostly originated from polymorphic repeat-rich genomic regions. Predicted gene targets of these sRNAs, from 10 different host species, were enriched for immunity-related functional domains. Predicted A. thaliana gene targets of S. sclerotiorum sRNAs were significantly more down-regulated during infection than other genes. A. thaliana gene targets were also more likely to contain single nucleotide polymorphisms (SNPs) associated with quantitative disease resistance. In conclusion, sRNAs produced by S. sclerotiorum are likely capable of silencing immunity components in multiple hosts. Prediction of fungal sRNA targets in host plant genomes can be combined with other global approaches, such as genome wide association studies and transcriptomics, to assist identification of plant genes involved in disease resistance.

plant biology↗

bioRxiv2017

Shifts in diversification rates and host jump frequencies shaped the diversity of host range among Sclerotiniaceae fungal plant pathogens

The range of hosts that a parasite can infect in nature is a trait determined by its own evolutionary history and that of its potential hosts. However, knowledge on host range diversity and evolution at the family level is often lacking. Here, we investigate host range variation and diversification trends within the Sclerotiniaceae, a family of Ascomycete fungi. Using a phylogenetic framework, we associate diversification rates, the frequency of host jump events, and host range variation during the evolution of this family. Variations in diversification rate during the evolution of the Sclerotiniaceae define three major macro-evolutionary regimes with contrasted proportions of species infecting a broad range of hosts. Host-parasite co-phylogenetic analyses pointed towards parasite radiation on distant hosts long after host speciation (host jump or duplication events) as the dominant mode of association with plants in the Sclerotiniaceae. The intermediate macro-evolutionary regime showed a low diversification rate, high frequency of duplication events, and the highest proportion of broad host range species. Consistent with previous reports on oomycete parasites, our findings suggest that host jump and radiation, possibly combined with low speciation rates, could associate with the emergence of generalist pathogens. These results have important implications for our understanding of fungal parasites evolution and are of particular relevance for the durable management of disease epidemics.

evolutionary biology↗