Comparative histone modification profiling revealed developmentally regulated acetylation on upstream promoters of C4 genes and potential C4 regulators

We analysed genome-wide histone H3 lysine 4 trimethylation and histone H3 lysine 9 acetylation, two modifications typically associated with active genes, in meristematic cells at the base and expanding cells in the maturing zone of the maize (Zea mays) leaf. These data were compared to transcript levels of associated genes. Our data revealed that for individual genes fold-changes in histone modification and transcript abundance were much better correlated than absolute intensities. When focusing on regulated modification sites, we identified secondary upstream H3 lysine 9 acetylation peaks (SUPs) on upstream promoter regions of approximately 6% of all acetylated genes. SUPs showed stronger regulation than the previously described acetylation peaks at transcription initiation sites, were more often found on genes that were upregulated towards the maturing zone than on downregulated genes, and were significantly enriched on photosynthetic genes. We identified SUPs on all genes encoding enzymes of the C4 cycle. Moreover, SUPs were enriched in four lists of candidate C4-associated genes that were derived from previous transcriptomic studies. Based on these data, we used highly regulated SUPs as an epigenetic mark to identify new genes potentially involved in C4 metabolism. This approach also allowed the identification of ethylene response elements as highly enriched cis-acting elements in SUP regions. Our data suggest co-evolution of epigenetic promoter elements during the establishment of C4 photosynthesis. Overall design: Comparative analysis of H3K9ac, H3K4me3 and the transcription between two developmental zones within one maize leaf.

4

Perduns R, Horst-Niessen I, Peterhansel C