Florigen-Encoding Genes of Day-Neutral and Photoperiod-Sensitive Maize Are Regulated by Different Chromatin Modifications at the Floral Transition

The activity of the maize (Zea mays) florigen geneZEA CENTRORADIALIS8(ZCN8) is associated with the floral transition in both day-neutral temperate maize and short-day (SD)-requiring tropical maize. We analyzed transcription and chromatin modifications at theZCN8locus and its nearly identical paralogZCN7during the floral transition. This analysis was performed with day-neutral maize (Zea maysssp.mays), where flowering is promoted almost exclusively via the autonomous pathway through the activity of the regulatory geneindeterminate1(id1), and tropical teosinte (Zea maysssp.parviglumis) under floral inductive and noninductive photoperiods. Comparison ofZCN7/ZCN8histone modification profiles in immature leaves of nonfloweringid1mutants and teosinte grown under floral inhibitory photoperiods reveals that bothid1floral inductive activity and SD-mediated induction result in histone modification patterns that are compatible with the formation of transcriptionally competent chromatin environments. Specific histone modifications are maintained during leaf development and may represent a chromatin signature that favors the production of processedZCN7/ZCN8messenger RNA in florigen-producing mature leaf. However, whereasid1function promotes histone H3 hyperacetylation, SD induction is associated with increased histone H3 dimethylation and trimethylation at lysine-4. In addition,id1and SD differently affect the production ofZCN7/ZCN8antisense transcript. These observations suggest that distinct mechanisms distinguish florigen regulation in response to autonomous and photoperiod pathways. Finally, the identical expression and histone modification profiles ofZCN7andZCN8in response to floral induction suggest thatZCN7may represent a second maize florigen.