Abstract
SUMMARYHeterochromatin is characterized by specific histone post-translational modifications such as the di- and tri-methylation of histone H3 on lysine 9 (H3K9me2/3), which direct the recruitment of ‘reader’ proteins to chromatin. In the fungal phytopathogen, Zymoseptoria tritici, deletion of the H3K9 methyltransferase gene kmt1, results in a global increase in the expression of transposable elements (TEs), genome instability and loss of virulence. Here we have identified two Z. tritici chromodomain proteins, Cbx1 and Cbx2, that recognise H3K9me modifications. Cbx1 is a Heterochromatin Protein 1 homolog that binds H3K9me2/3 in vitro and associates with heterochromatic loci in vivo. Transcriptomic analysis also indicates that Cbx1 and Kmt1 regulate overlapping sets of protein-encoding genes. However, unlike Δkmt1 mutants, Δcbx1 strains do not exhibit a global increase in TE expression and have only a partial reduction in virulence, suggesting the existence of additional H3K9me reader proteins. Accordingly, we have identified a fungal-specific chromodomain protein, Cbx2, that binds H3K9me3 in vitro. Strikingly, the growth defects of Δcbx1 Δcbx2 double mutants closely resemble those of Δkmt1 consistent with Cbx1 and Cbx2 playing redundant roles in gene silencing. Overall, the data suggest that key functions of H3K9me modifications are mediated by a combination of Cbx1 and Cbx2.
Publisher
Cold Spring Harbor Laboratory
Cited by
1 articles.
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