Figure 7.

Model of florigen regulation in autonomous maize and photoperiod-induced teosinte. Autonomous maize (left) requires ID1 regulatory protein activity (orange stars) in developing leaves to establish chromatin modifications that allow the expression of florigen genes (ZCN7 and ZCN8). Thus, the id1 gene acts in immature leaves to establish a chromatin signature and prime the leaf for florigen synthesis as the leaf develops. Active chromatin is specified by H3ac. Once the distal portion of the leaf develops, another signal (unknown) activates florigen production in leaf vasculature, which then migrates to the shoot apical meristem (SAM) to activate flowering genes (purple dotted line). The autonomous signal may consist, partly, of changes in metabolic activity. Metabolic changes could also indirectly activate florigen production (?). In teosinte (right), floral induction is dependent on SD photoperiods and the circadian clock to activate florigen production. Similar to id1, the photoperiod pathway also establishes chromatin modifications in immature leaves, which enable florigen synthesis in mature leaves, but the pattern of histone modifications related to its activity is different from the one created by id1 in the autonomous pathway (i.e. open chromatin is specified by H3K4me2/H3K4me3). The horizontal dashed lines across the mature maize and teosinte leaves delineate the regions of the immature, developing leaf zone (bottom) from the mature leaf blade (top).