ARS | Publication request: Outstanding: the Dispensable Chromosomes of Mycosphaerella Graminicola

Submitted to: Fungal Genetics Conference Proceedings
Publication Type: Abstract
Publication Acceptance Date: January 17, 2009
Publication Date: March 17, 2009
Citation: M'Barek, S.B., Van Der Lee, T.A., Wittenberg, A.H., Maliepaard, C., Crane, C.F., Dhillon, B., Goodwin, S.B., Schouten, H.J., Kema, G.H. 2009. Outstanding: the Dispensable Chromosomes of Mycosphaerella Graminicola. Fungal Genetics Conference Proceedings. 56:102

Technical Abstract: Analyses of two genetic linkage maps of the wheat pathogen Mycosphaerella graminicola identified chromosomes that were present in both parents of each cross but absent in 15-20 % of the progeny so appeared to be dispensable. This high genome plasticity among isolates was further confirmed with a Comparative Genomic Hybridization whole-genome array based on the finished genome of M. graminicola (http://genome.jgi-psf.org/Mycgr1/Mycgr1.home). These analyses revealed numerous chromosome number polymorphisms (CNPs). Chromosomes 14-21 were regularly absent among isolates; chromosomes 1-13 contain the essential M. graminicola genome. Progeny isolates and field strains can miss up to three chromosomes with no obvious effect on viability or pathogenicity. Further genetic analyses demonstrated that CNPs arise from aberrations during meiosis, usually nondisjunction during meiosis II. Overall, M. graminicola has the highest number of dispensable chromosomes reported. They vary from 0.41 to 0.77 Mbp; 40% of the chromosomal complement and 11.6% of the genome. The core chromosomes 1-13 differed strikingly from dispensable chromosomes 14-21. The latter are smaller and have significantly lower gene densities. Most of these genes are duplicated elsewhere in the genome and show a different codon usage. Dispensable chromosomes also contained a high density of transposons, pseudogenes and unclassified genes, which could encode proteins with novel functions. There was little conserved synteny between the chromosomes of M. graminicola and those of other Dothideomycetes, particularly for those that are dispensable. We hypothesize that the plasticity of the M. graminicola genome plays an important role in yet unknown processes of adaptation.