Godiard, L. | bioRxiv Science

bioRxiv2025

Phylogenomics of Plasmopara halstedii reveals genomic regions associated with the breakdown of sunflower downy mildew resistance genes

O_LIUnderstanding the genetic diversity and evolutionary history of plant pathogens is crucial for effective disease management strategies. Sunflower downy mildew, caused by the oomycete Plasmopara halstedii, is a worldwide threat to the sunflower oil crop. We aimed to explain through phylogenomic studies how downy mildew resistance breakdown occurred recurrently in the last decades in France, leading to new virulence profiles. C_LIO_LIWe assembled high-quality genomes of three founder pathotypes of Pl. halstedii. Performing comparative genomic analyses, population genetics, and phylogenomic analyses, we studied the genomic structure among the 16 reference French pathotypes of Pl. halstedii. C_LIO_LIWe revealed a conserved genomic organisation among pathotypes and a strong synteny with other Peronosporales species. The history of Pl. halstedii invasion in France over the last 60 years was documented by identifying founder strains and their admixture patterns. The emergence of pathotypes with broader virulence spectra and therefore capable of overcoming host resistance was associated with genomic reshuffling. We highlighted genomic mosaicism in admixed pathotypes and identified regions associated with the breakdown of host resistance genes harbouring putative effector genes. C_LIO_LIOur findings provide insights into evolutionary mechanisms underlying plant pathogen host adaptation, which has implications for a sustainable deployment of multiple resistance genes. C_LI

plant biology↗

bioRxiv2020

The plant endoplasmic reticulum is both receptive and responsive to pathogen effectors

The endoplasmic reticulum (ER) is the entry point to the secretory pathway and, as such, is critical for adaptive responses to biotic stress, when the demand for de novo synthesis of immunity-related proteins and signalling components increases significantly. Comprised of a network of interconnected tubules and cisternae, the architecture of the ER is highly pleomorphic and dynamic, rapidly remodelling to meet new cellular requirements. During infection with the hemi-biotrophic phytopathogen, Pseudomonas syringae pv. tomato DC3000, the ER in cells immediately adjacent to established bacterial colonies condenses into knot-like structures, reminiscent of fenestrated sheets. Based on known temporal dynamics of pathogen effector delivery and initial bacterial multiplication, the timing of these observed morphological changes is rapid and independent of classical elicitor activation of pathogen-triggered immunity. To further investigate a role for ER reconfiguration in suppression of plant immunity we identified a conserved C-terminal tail-anchor domain in a set of pathogen effectors known to localize to the ER and used this protein topology in an in silico screen to identify putative ER-localised effectors within the effectorome of the oomycete Phytophthora infestans. Subsequent characterization of a subset of 15 candidate tail-anchored P. infestans effectors revealed that 11 localised to the ER and/or Golgi. Notably, transient expression of an ER-localised effector from the closely related oomycete, Plasmopara halstedii, reconfigured the ER network, revealing intimate association of labelled ER with perinuclear chloroplasts and clusters of chloroplasts, potentially facilitating retrograde signalling during plant defence.

plant biology↗