Karyotype evolution in Fusarium

• Published in: IMA fungus Vol. 9; no. 1; pp. 13 - 26
• Main Authors: Waalwijk, Cees, Taga, Masatoki, Zheng, Song-Lin, Proctor, Robert H, Vaughan, Martha M, O'Donnell, Kerry
• Format: Journal Article
• Language: English
• Published: England BioMed Central 01-06-2018; International Mycological Association
• Subjects: ACCESSORY; Agriculture; CHROMOSOME; Chromosome number; Chromosomes; Food contamination & poisoning; Fungi; Fusarium; GENOME; Genomes; Karyotypes; NOR; Nucleoli; Nucleotide sequence; PATHOGEN; Phylogenetics; PHYLOGENY; QPCR; RNA polymerase; RPB1; RPB2; Small mammals; Species; SUPERNUMERARY; Supernumerary chromosomes; Telomeres; Veterinary medicine; Whole genome sequencing; NOR; genome; chromosome; RPB2; pathogen; phylogeny; qPCR; RPB1; supernumerary; accessory
• ISSN: 2210-6340; 2210-6359; 2210-6359
• DOI: 10.5598/imafungus.2018.09.01.02

The germ tube burst method (GTBM) was employed to examine karyotypes of 33
species representative of 11 species complexes that span the phylogenetic breadth of the genus. The karyotypes revealed that the nucleolar organizing region (NOR), which includes the ribosomal rDNA region, was telomeric in the species where it was discernible. Variable karyotypes were detected in eight species due to variation in numbers of putative core and/or supernumerary chromosomes. The putative core chromosome number (CN) was most variable in the
(CN = 9‒12) and
(CN = 9+1 and 18-20) species complexes. Quantitative real-time PCR and genome sequence analysis rejected the hypothesis that the latter variation in CN was due to diploidization. The core CN in six other species complexes where two or more karyotypes were obtained was less variable or fixed. Karyotypes of 10 species in the
species complex, which is the most derived lineage of
, revealed that members of this complex possess the lowest CN in the genus. When viewed in context of the species phylogeny, karyotype evolution in
appears to have been dominated by a reduction in core CN in five closely related complexes that share a most recent common ancestor (
and
CN = 8-9,
CN = 8,
CN = 7,
CN = 4-5) but not in the sister to these complexes (
CN = 11,
CN = 11 and
CN = 10-12). CN stability is best illustrated by the
subclade, where the only changes observed since it diverged from other fusaria appear to have involved two independent putative telomere to telomere fusions that reduced the core CN from five to four, once each in the
and
subclades. Results of the present study indicate a core CN of 4 may be fixed in the latter subclade, which is further distinguished by the absence of putative supernumerary chromosomes. Karyotyping of fusaria in the not too distant future will be done by whole-genome sequencing such that each scaffold represents a complete chromosome from telomere to telomere. The CN data presented here should be of value to assist such full genome assembling.