title: The dispensable chromosome of Leptosphaeria maculans shelters an effector gene conferring avirulence towards Brassica rapa.
abstract: Phytopathogenic fungi frequently contain dispensable chromosomes, some of which contribute to host range or pathogenicity. In Leptosphaeria maculans, the stem canker agent of oilseed rape (Brassica napus), the minichromosome was previously suggested to be dispensable, without evidence for any role in pathogenicity. Using genetic and genomic approaches, we investigated the inheritance and molecular determinant of an L. maculans-Brassica rapa incompatible interaction. Single gene control of the resistance was found, while all markers located on the L. maculans minichromosome, absent in the virulent parental isolate, co-segregated with the avirulent phenotype. Only one candidate avirulence gene was identified on the minichromosome, validated by complementation experiments and termed AvrLm11. The minichromosome was frequently lost following meiosis, but the frequency of isolates lacking it remained stable in field populations sampled at a 10-yr time interval, despite a yearly sexual stage in the L. maculans life cycle. This work led to the cloning of a new 'lost in the middle of nowhere' avirulence gene of L. maculans, interacting with a B. rapa resistance gene termed Rlm11 and introgressed into B. napus. It demonstrated the dispensability of the L. maculans minichromosome and suggested that its loss generates a fitness deficit.
authors: INRA, UR1290 BIOGER, Avenue Lucien Brétignières, BP 01, F-78850, Thiverval-Grignon, France.
authors: Marie-Hélène
authors: MH
authors: Balesdent
authors: INRA, UR1290 BIOGER, Avenue Lucien Brétignières, BP 01, F-78850, Thiverval-Grignon, France.
authors: Isabelle
authors: I
authors: Fudal
authors: INRA, UR1290 BIOGER, Avenue Lucien Brétignières, BP 01, F-78850, Thiverval-Grignon, France.
authors: Bénédicte
authors: B
authors: Ollivier
authors: INRA, UR1290 BIOGER, Avenue Lucien Brétignières, BP 01, F-78850, Thiverval-Grignon, France.
authors: Pascal
authors: P
authors: Bally
authors: INRA, UR1290 BIOGER, Avenue Lucien Brétignières, BP 01, F-78850, Thiverval-Grignon, France.
authors: Jonathan
authors: J
authors: Grandaubert
authors: INRA, UMR1349 IGEPP, BP35327, F-35653, Le Rheu Cedex, France.
authors: Frédérique
authors: F
authors: Eber
authors: INRA, UMR1349 IGEPP, BP35327, F-35653, Le Rheu Cedex, France.
authors: Anne-Marie
authors: AM
authors: Chèvre
authors: CETIOM, Avenue Lucien Brétignières, BP 01, F-78850, Thiverval-Grignon, France.
authors: Martine
authors: M
authors: Leflon
authors: INRA, UR1290 BIOGER, Avenue Lucien Brétignières, BP 01, F-78850, Thiverval-Grignon, France.
authors: Thierry
authors: T
authors: Rouxel
mesh_terms: D001203:Ascomycota / Q000235:genetics* / Q000472:pathogenicity*; D029688:Brassica napus / Q000235:genetics / Q000382:microbiology; D029741:Brassica rapa / Q000235:genetics / Q000382:microbiology*; D015825:Chromosomes, Fungal / Q000235:genetics*; D003001:Cloning, Molecular; D003433:Crosses, Genetic; D060467:Disease Resistance / Q000235:genetics; D005800:Genes, Fungal; D054884:Host-Pathogen Interactions / Q000235:genetics*; D008540:Meiosis; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D014774:Virulence / Q000235:genetics