Studying sexual reproduction in Leptosphaeria maculans, the causal agent of blackleg disease of rapeseed

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Nguyen, Tinh-Suong | Balesdent, Marie-Hélène

Edité par CCSD -

International audience. Plant-associated fungi have an important role in our ecosystems, either through beneficial, neutral or harmful interactions. In particular, phytopathogenic fungi represent a threat to global food security. Rapeseed (Brassica napus), the world’s second-largest oilseed crop, is mainly threatened by the ascomycete Leptosphaeria maculans. The latter displays a complex life cycle switching from an asymptomatic colonization (biotrophic stage) followed by a necrotrophic phase, and eventually a saprotrophic step. During the saprotrophic stage, sexual reproduction take place on stems debris. This step is paramount in its life and pathogenic cycle since sexual reproduction (i) favors genetic recombination and appearance of new pathogenicity traits and (ii) produces ascospores that are the main inoculum throughout the plant life. Sexual reproduction in L. maculans is controlled in laboratories, but this stage has never been detailed. Our first aim of this project is to describe sexual reproduction per se. This involves identifying male and female gametes, and characterizing the different steps between fertilization and production of ascospores. Under laboratory conditions, fruiting bodies (pseudothecia) are mature after 3-4 weeks of culture. Nevertheless, the precise dynamics of pseudothecia production is not yet known. Besides, the development of fruiting bodies depends on environmental conditions that are not yet fully understood. At a molecular level, we aim to determine key genes involved in the successive stages. The second aim linked to sexual reproduction consists in studying the epigenetic mechanism RIP (Repeat-Induced Point mutation) occurring beforekaryogamy. This genome defense mechanism detects duplicated sequences and induces C-to-T mutations and methylation in repeats. The mechanism of RIP and its ability to recognize duplications throughout the genome are not well understood. This specific process can result in the emergence of new pathogenicity-related alleles, and thus new virulent strains. The first results of this project will be presented

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