Investigating the involvment of the chromatin state and transcription factors in the control of effector gene expression in Leptosphaeria maculans.
Résumé
Leptosphaeria maculans, a hemibiotrophic fungus responsible of stem canker, colonises oilseed rape in two stages: an early stage of cotyledon or leaf colonisation, and a late colonisation stage during which the fungus colonises systemically without visible symptom the plant before stem canker appears. L. maculans presents a bipartite genome structure alternating gene-rich and transposable element (TE)-rich regions. TE-rich regions, which encompass one third of the genome, are enriched in putative effector-encoding genes that present the same expression pattern (no or a low expression level during in vitro growth and a strong over-expression during early infection in cotyledons and leaves; ‘early’ effectors). In contrast, gene-rich regions were recently reported to contain putative effector-encoding genes specifically expressed during the late stages of stem infection (‘late’ effectors). We have previously investigated the involvement of the chromatin structure of repeat-rich regions on the expression of ‘early’ effector genes: RNAi silencing of two genes encoding key players in heterochromatin assembly through histone modification H3K9me3, HP1 and KMT1, induced an over-expression of genes located in AT-isochores, particularly ‘early’ effector genes but no modification of ‘late’ effector genes expression. Here, we performed directed mutagenesis on this fungus using CRISPR-CAS9 technology. During my latest months of thesis I mutated both chromatin key remodeling proteins (KMT1, KMT6 and KDM8) and transcription factors. In this presentation I will describe the impact of these inactivations on effector gene expression and pathogenicity.