Flower and shoot fasciation: From phenomenology to the construction of models of apical meristem transformations

The review considers the phenomenon of fasciation arising due to the enlargement of shoot or floral meristem. The system of CLAVATA-WUSCHEL proteins controls the pool of stem cells in the surface layers of the shoot apical meristem. The analysis of the literature allowed clarifying the role of the WUSCHEL (WUS) gene in the creation of positional signals for the emergence of leaf primordia and procambial strands. The hypothesis is put forward about the new regulatory cascade PINHEAD/ZWILLE-WUSCHEL involved in the positional control of auxin fluxes and determining the optimal density of vascular bundles in the tissue volume. The examples of various types of shoot and flower fasciation are presented: radial, linear, and ring fasciation, defasciation). The model of anatomo-morphological changes accompanying fasciation is suggested.