Reference Quality Genome Assemblies of Three Parastagonospora nodorum Isolates Differing in Virulence on Wheat

Parastagonospora nodorum, the causal agent of Septoria nodorum blotch of wheat, has emerged as a model necrotrophic fungal organism for the study of host-microbe interactions. To date, three necrotrophic effectors have been identified and characterized from this pathogen, including SnToxA, SnTox1, and SnTox3. Necrotrophic effector identification was greatly aided by the development of a draft genome of Australian isolate SN15 via Sanger sequencing, yet remained largely fragmented. This research presents the development of near-finished genomes of P. nodorum isolates Sn4, Sn2000, and Sn79-1087 using long-read sequencing technology. RNAseq analysis of isolate Sn4 consisting of eight time-points covering various developmental and infection stages mediated the annotation of 13,379 genes. Analysis of these genomes revealed large-scale polymorphism between the three isolates, including the complete absence of contig 23 from isolate Sn79-1087 and a region of genome expansion on contig 10 in isolates Sn4 and Sn2000. Additionally, these genomes exhibit the hallmark characteristics of a 'two-speed' genome, being partitioned into two distinct GC-equilibrated and AT-rich compartments. Interestingly, isolate Sn79-1087 contains a lower proportion of AT-rich segments, indicating a potential lack of evolutionary hot spots. These newly sequenced genomes, consisting of telomere to telomere assemblies of nearly all 23 P. nodorum chromosomes provides a robust foundation for the further examination of effector biology and genome evolution.

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