Towards an understanding of spiral patterning in the Sargassum muticum shoot apex

Classic studies of leaf placement (phyllotaxy) showed that two different mechanisms occur in land plants. In mosses, leaf placement is determined by the plane of cell division within the single apical cell, whereas in seed plants auxin acts as a morphogen that specifies leaf positioning. Linardić and Braybrook examined how the spiral pattern of phyllotaxy is determined in the brown alga Sargassum muticum. Although multicellularity arose independently in brown algae and plants, there are similarities in their indeterminate structure and apical meristem-like regions. The authors showed that in the brown alga the spiral orientation of the apical cell cleavage is unlinked to the spiral orientation of phyllotaxy. Destruction of the apical cell was frequently followed by reorganization and re-establishment of phyllotaxy, suggesting that it is a self-organizing principle, but there is no evidence for auxin involvement. BioRxiv 10.1101/135806