The Physcomitrella patens chromatin adaptor PpMRG1 interacts with H3K36me3 and regulates light-responsive alternative splicing

Plants perceive dynamic light conditions and optimize their growth and development accordingly by regulating gene expression at multiple levels. Alternative splicing (AS), a widespread mechanism in eukaryotes that post-transcriptionally generates two or more messenger RNAs (mRNAs) from the same pre-mRNA, is rapidly controlled by light. However, a detailed mechanism of light-regulated AS is still not clear. In this study, we demonstrate that histone 3 lysine 36 trimethylation (H3K36me3) rapidly and differentially responds to light at specific gene loci with light-regulated intron retention (IR) of their transcripts in the moss Physcomitrella patens. However, the level of H3K36me3 following exposure to light is inversely related to that of IR events. Physcomitrella patens MORF-related gene 1 (PpMRG1), a chromatin adaptor, bound with higher affinity to H3K36me3 in light conditions than in darkness and was differentially targeted to gene loci showing light-responsive IR. Transcriptome analysis indicated that PpMRG1 functions in the regulation of light-mediated AS. Furthermore, PpMRG1 was also involved in red light-mediated phototropic responses. Our results suggest that light regulates histone methylation, which leads to alterations of AS patterns. The chromatin adaptor PpMRG1 potentially participates in light-mediated AS, revealing that chromatin-coupled regulation of pre-mRNA splicing is an important aspect of the plant's response to environmental changes.