Genome analysis of the plant pathogenic ascomycete Leptosphaeria maculans; mapping mating type and host specificity loci

Abstract

A genetic and physical map has been developed for the loculoascomycete Leptosphaeria maculans, a pathogen of oilseed Brassicas. The genetic map was constructed from 58 F(1) progeny and comprises 155 amplified fragment length polymorphic (AFLP) markers, three random amplified polymorphic DNA (RAPD) markers, the mating type locus and a host specificity locus conferring the ability to form lesions on Brassica juncea. Twenty-one linkage groups, 5 pairs, and 18 unlinked markers were assigned, and the genome size was 1520 cM. Pulsed field gel electrophoresis experiments showed that the parental isolates each had 16 chromosomes and a genome size of about 33.5 Mb. Attempts to anchor a large number of markers to chromosomes were hampered by difficulties in converting AFLPs into RFLP markers, and because many markers bound to every chromosome, indicating that L. maculans has a high level of dispersed repetitive sequences. This fungus displays chromosomal length polymorphisms, but in the cross examined, the linkage and physical maps were essentially congruent and there was no evidence of translocations. The host specificity locus is 18 cM from the nearest AFLP marker and is located on a chromosome sized 1.85 Mb in the virulent parent. The mating type locus is on a chromosome sized 2.6 Mb and coincident on an AFLP marker amplified from the virulent parent. The derived amino acid sequence of part of this marker has some conserved amino acids present in the High Mobility Group DNA binding domain of MAT-2 mating type genes of other ascomycetes.

Genetic linkage map of Phaeosphaeria nodorum, the causal agent of stagonospora nodorum blotch disease of wheat

“…Recently, genetic linkage maps have been constructed for ascomycete pathogens causing canola blackleg (Leptosphaeria maculans) (Cozijnsen et al 2000), septoria tritici wheat blotch (Mycosphaerella graminicola) (Goodwin et al 2007), and banana black leaf streak (Mycosphaerella fijiensis) (Manzo-Sánchez et al 2008) diseases. Based on linkage analysis, molecular markers associated with genetic loci conferring mating type (Kema et al 2002;Kubisiak and Milgroom 2006;Kuhn et al 2006), host specificity, vegetative incompatibility (Kubisiak and Milgroom 2006) and avirulence (Kema et al 2002) have been reported.…”

Leptosphaeria maculans, the Causal Agent of Blackleg Disease of Brassicas

“…L. maculans is haploid, outcrossing, can be readily transformed, and has a genome size of about 34 Mb, which is similar to that of other ascomycetes (Kupfer et al, 1997). Its chromosomes are of a size range (about 0.7 to 3.5 Mb) and number (16) for optimal resolution by electrophoretic karyotyping (Taylor et al, 1991;Howlett, 1997;Cozijnsen et al, 2000).…”

“…Another cotyledonary avirulence gene, alm1, has been mapped by a research group at University of Wisconsin (Madison, WI) (Pongam et al, 1998). The mapping of this gene, as well as that of a gene conferring the ability to attack both cotyledons and stems of B. juncea Cozijnsen et al, 2000) is discussed later. The presence of a small number of loci controlling (a)virulence is suggested by a study of environmental and genetic components of variance in the virulence of 24 Australian isolates of L. maculans on five B. napus cultivars (Pang and Halloran, 1996).…”

“…Preliminary genetic maps have been developed for L. maculans by Pongam et al (1998) and Cozijnsen et al (2000). Unfortunately it is difficult to integrate these two maps as the markers (AFLP) used to generate them are not readily transferable.…”

“…Two markers flanked alm1 (3.1 and 8.1 cM distant). Cozijnsen et al (2000) constructed a genetic map comprising 155 AFLP markers, three RAPD markers, the mating type locus, and a host specificity locus. The host specificity locus conferred the ability to form lesions on cotyledons and stems of B. juncea from 58 F 1 progeny of a cross between Australian isolates C13 and M1 (IBCN17 and 18, respectively).…”