Describing radial patterning and leaf polarity in plants using a model of a dynamic shoot apical meristem with primordia initiation

Sammanfattning: The initiation of leaf and flower primordia in plants occurs in the shoot apical meristem and results in visible large–scale regular patterns of organs. It has previously been proposed that the initiation of new primordia is triggered by the plant hormone auxin by a mechanism that is confined to the outermost epidermal layer of the meristem. Recent experiments suggest that the genes KANADI (KAN) and REVOLUTA (REV), involved in determining the polarity of leaves, might also be involved in the primordia initiation mechanism. Here we introduce and analyse in detail a model which aims to reproduce the distinct KAN and REV pattern as observed in confocal microscopy, along with the dynamics of leaf primordia initiation. In accordance with experimental results, REV expression in the meristem is regulated by microRNAs, and a gap consisting of cells expressing neither KAN nor REV lies in the boundary between regions of KAN and REV expression. Antagonistic KAN and REV interactions are shown to be sufficient to set a mutually exclusive KAN/REV pattern with a gap. Model predictions suggest a self-activation mechanism for the KAN gene expression. When the model is combined with a hypothesis of active transportation of auxin by polarised PIN1 proteins, a whorled organ pattern was generated. Model considerations points to a need of investigating the signalling pathway between auxin and PIN1 in more detail.