Influence of histone modifications on effector gene expression in the plant pathogenic fungus Leptosphaeria maculans.
2017
Soyer, Jessica | Clairet, Colin | Gervais, Julie | Balesdent, Marie-Helene | Connolly, Lanelle R | Freitag, Michael | Rouxel, Thierry | Fudal, Isabelle | BIOlogie et GEstion des Risques en agriculture (BIOGER) ; Institut National de la Recherche Agronomique (INRA)-AgroParisTech | Center for Genome Research and Biocomputing, Department of Biochemistry and Biophysics ; Oregon State University (OSU) | Ruhr University Bochum = Ruhr-Universität Bochum (RUB)
Leptosphaeria maculans, the fungus responsible for stem canker of oilseed rape (Brassica napus), presents a particular genome structure divided into gene-rich and transposable element (TE)-rich regions. The latter are proposed to be heterochromatic domains, as they are gene-poor, TE-rich and present lower recombination rates than gene-rich regions. While overall gene-poor, TE-rich regions are enriched for putative effector genes specifically expressed during the early stages of plant infection (‘early’ effector genes). In contrast, effector genes expressed during the late stages of infection (endophytic growth and stem necrosis, ‘late’ effector genes) are located in gene-rich regions. We investigated the concerted expression of ‘early’ effector genes by assessing whether TE-rich regions could be targets of reversible chromatin modifications that affect the regulation of effector gene expression. We first examined the involvement of one histone modification, histone H3 lysine 9 tri-methylation (H3K9me3) in chromatin-based regulation of effector gene expression. For this purpose, we silenced expression of two key players in heterochromatin assembly and maintenance, HP1 and KMT1, by RNAi. Silencing of HP1 and KMT1 led to an over-expression of ‘early’ effector genes in TE-rich regions during in vitro growth (but no induction of ‘late’ effector gene expression). The increase of expression was associated with a reduction of H3K9 tri-methylation at two effector-encoding gene loci. Our data strongly suggest that a chromatin-based control, mediated by HP1 and KMT1, represses the expression of at least part of the ‘early’ effector genes located in TE-rich regions during growth in axenic culture. We are currently investigating the role of another key player in heterochromatin assembly, KMT6, involved in the heterochromatic-associated histone modification H3K27me3, on the control of effector gene expression
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