Biomedical subjects
Publications and source records attributed to Thomas Badet.
The repeat-induced point mutation (RIP) targets repeated sequences, such as transposable elements, in filamentous fungi. Host-transposable element coevolutionary dynamics have shaped taxonomically restricted eukaryotic defense systems, likely built on conserved ancestral mechanisms. Key questions surrounding homology recognition remain unresolved, and RIP offers a unique opportunity to answer them.
Fungal genome sizes exhibit more than a 100-fold variation, largely driven by the expansion of repetitive sequences such as transposable elements (TEs). Silencing mechanisms targeting TEs at the epigenetic or transcript level have independently evolved in many lineages. In fungi, repeat-induced point mutation (RIP) targets TEs by recognizing repetitive sequences and inducing mutagenesis. However, the prevalence of RIP across the fungal kingdom and the fidelity of the canonical C-to-T mutation signatures remain unclear. In this study, we address these gaps by tracking shifts in genome architecture across the fungal kingdom. We find that a striking approximately 30-fold increase in genome size within a clade of leotiomycetes is associated with the absence of several RIP-related genes, suggesting a relaxation of genome defense mechanisms during this expansion. To track the impact of genome defenses, we designed a quantitative screen for RIP-like mutation signatures. The phylum of ascomycetes was unique in showing enrichment in mutation signatures in non-coding and repetitive sequences, consistent with a phylogenetically restricted occurrence of RIP-like genome defense systems. Then, we performed a phylogeny-aware association study to identify gene functions associated with RIP-like mutation signatures. We identified a zinc-finger protein as the strongest candidate underpinning a novel mechanism of genome defenses. Our findings reveal the multifaceted drivers of genome defense systems and their close ties to genome size evolution in fungi, particularly in lineages with evidence for recent RIP activity, highlighting how proximate molecular mechanisms can shape genome evolution on deep phylogenetic scales.
In response to necrotrophic fungal pathogens, plants often display quantitative disease resistance (QDR), an immune response with complex genetic determinants. Due to their diversity and small phenotypic effect, the genetic bases of QDR are challenging to characterize. Here, we used genome-wide association mapping in Arabidopsis thaliana natural populations to identify novel determinants of QDR against the fungal pathogen Sclerotinia sclerotiorum. We found that presence-absence polymorphism of the AT4TE56270 Copia transposable element (TE) upstream of the cysteine-rich receptor-like kinase 8 (CRK8) gene is associated with QDR. The presence of the TE associates with higher CRK8 expression in healthy and inoculated plants and increased QDR. The constitutive knockdown of CRK8 reduced QDR, hydrogen peroxide production, and the expression of defense genes upon inoculation. Transcriptome analysis revealed altered defense pathways and salt responses in CRK8 mutants, including impaired glutathione and camalexin biosynthesis, likely contributing to disease susceptibility. Mutants in CRK8 showed altered seed germination on salt, and the absence of AT4TE56270 is associated with enhanced seed germination under salt stress in A. thaliana natural populations. These results reveal a trade-off between salt tolerance and defense against S. sclerotiorum associated with presence-absence polymorphism of a TE.