Pangenome graph analysis reveals extensive effector copy-number variation in spinach downy mildew

Area of Science:

• Genomics
• Plant Pathology
• Evolutionary Biology

Background:

• Plant pathogens rapidly adapt, challenging disease management strategies.
• Comparative genomics aids in understanding pathogen adaptation processes.
• Peronospora effusa causes significant economic losses in spinach cultivation worldwide.

Purpose of the Study:

• To construct and annotate the first pangenome graph of an oomycete plant pathogen.
• To analyze genomic variation and identify adaptation mechanisms.
• To provide a high-resolution framework for studying pathogen evolution.

Main Methods:

• Generated telomere-to-telomere genome assemblies for six diverse Peronospora effusa isolates.
• Developed a multi-genome method to construct a pangenome graph.
• Analyzed the graph to identify synteny-based single-copy orthogroups and gene variations.

Main Results:

• Peronospora effusa genomes exhibit high conservation in chromosomal structure and gene content.
• Transposable element activity accounts for 80% of the observed genetic variation.
• Virulence-related genes show high variability, often in expanded gene clusters.

Conclusions:

• Pangenome graph analysis effectively captures genomic variation at high resolution.
• Transposable elements are key drivers of adaptation and variation in P. effusa.
• This framework facilitates the study of plant pathogen biology and evolution.