Postdoc Department of Plant Pathology, Kansas State University
A common mechanism shared by microbial pathogens to overcome host-immunity and cause disease is the use of secreted effectors. Pathogens rapidly respond to in planta growth by activating specific developmental programs and effector genes in order to manipulate the host and cause infection. Interestingly, fungal effectors are tightly repressed during growth outside of the host. The underlying regulatory mechanisms leading to the specific activation of in planta development and effector expression and repression in other environments remain unclear. Epigenetic marks, including histone modifications, are commonly involved in transcriptional regulation in eukaryotic organisms in response to environmental stimuli. Given the localization of many effectors in repeat rich regions of the genome, and their global switch from a repressed to activated state, one hypothesis is that histone modification dynamics control this process. To test this hypothesis, we investigated methylation and acetylation histone modification dynamics at histone 3 Lysine 27. Mapping these modifications in a M. oryzae using ChIP-Seq revealed that H3K27me3 marked regions have low expression during in vitro growth, but are highly induced in planta, harboring half of the 28 characterized effector genes. Interestingly, analysis of a mutant lacking H3K27me3 shows re-location of H3K27ac to genes previous marked by H3K27me3 and their subsequent activation. These results support the hypothesis that epigenetic state switches are associated with altered gene expression. Evaluation of individual effector loci identified four patterns of histone modifications and transcriptional response, which suggests more than half effector genes are under the regulation either solely by H3K27me3 or by additive effects of H3K27me3 and H3K27ac. This work suggests an epigenetic regulatory network, mediated by histone modification dynamics at H3K27 controlling effector gene repression and activation during host colonization by fungi.
Coauthors: Jun Huang – Kansas State University;David Cook – Kansas State University