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

• Main Authors: Jonathan K. Richards, Nathan A. Wyatt, Zhaohui Liu, Justin D. Faris, Timothy L. Friesen
• Format: Article
• Language: English
• Published: Oxford University Press 2018-02-01
• Series: G3: Genes, Genomes, Genetics
• Subjects: Parastagonospora nodorum; genome sequencing; RNAseq; wheat; effector; Genome Report
• Online Access: http://g3journal.org/lookup/doi/10.1534/g3.117.300462

Parastagonospora nodorum, the causal agent of Septoria nodorum blotch in 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 it remained largely fragmented. This research presents the development of nearly 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 hotspots. These newly sequenced genomes, consisting of telomere-to-telomere assemblies of nearly all 23 P. nodorum chromosomes, provide a robust foundation for the further examination of effector biology and genome evolution.