A model study of the role of proteins CLV1, CLV2, CLV3, and WUS in regulation of the structure of the shoot apical meristem

In order to elucidate the role of proteins CLV1, CLV2, CLV3, and WUS in the mechanism underlying the maintenance of compartmental structure (spatial arrangement of the zones of biosynthesis of marker proteins) of the shoot apical meristem, a model of such mechanism was developed. Computational experiments led to biologically plausible solutions only when synthesis of substance W in a space between the organizing center and meristem apex was limited by the mechanism based on interaction of CLV3 with membrane receptor CLV1/CKV2 and lower boundary of the zone of W synthesis was determined by isoline of the corresponding threshold level of substance Y concentration. The model of the "reaction-diffusion" type formalizing the role proteins CLV1, CLV2, CLV3, and WUS can describe the basis of the mechanism underlying regulation of the compartmental structure of the shoot apical meristem and positioning of the organizing center in a certain site of the cell ensemble of such meristem.     

A systems approach to morphogenesis in Arabidopsis thaliana: II. Modeling the regulation of shoot apical meristem structure

Two models of the mechanism maintaining a zonal structure in the shoot apical meristem (SAM) were built based on the analysis of experimental data on the interactions between CLV1, CLV2, CLV3, and WUS genes and the concepts of their role in this mechanism. The first model, a simple one-dimensional model with two morphogens, which is a variant of Wolpert’s French flag model [1], describes the regulation of zone distribution along the SAM vertical axis. Despite a number of simplifications, this model has stationary solutions with biologically meaningful interpretation. The simplifying assumptions were successively abandoned in constructing a two-dimensional model of the mechanism underlying the regulation of SAM structure. This model provides a better understanding of the distributed system that regulates the SAM structure, and allows more detailed formalization of the modern concepts and experimental data concerning this mechanism.

     

3D analysis of mitosis distribution highlights the longitudinal zonation and diarch symmetry in proliferation activity of the Arabidopsis thaliana root meristem

To date CYCB1;1 marker and cortex cell lengths have been conventionally used to determine the proliferation activity of the Arabidopsis root meristem. By creating a 3D map of mitosis distribution we showed that these markers overlooked that stele and endodermis save their potency to divide longer than the cortex and epidermis. Cessation of cell divisions is not a random process, so that mitotic activity within the endodermis and stele shows a diarch pattern. Mitotic activity of all root tissues peaked at the same distance from the quiescent center (QC); however, different tissues stopped dividing at different distances, with cells of the protophloem exiting the cell cycle first and the procambial cells being the last. The robust profile of mitotic activity in the root tip defines the longitudinal zonation in the meristem with the proliferation domain, where all cells are able to divide; and the transition domain, where the cell files cease to divide. 3D analysis of cytokinin deficient and cytokinin signaling mutants showed that their proliferation domain is similar to that of the wild type, but the transition domain is much longer. Our data suggest a strong inhibitory effect of cytokinin on anticlinal cell divisions in the stele.     

A systems approach to morphogenesis in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>: II. Modeling the regulation of shoot apical meristem structure

Two models of the mechanism maintaining a zonal structure in the shoot apical meristem (SAM) were built based on the analysis of experimental data on the interactions between CLV1, CLV2, CLV3, and WUS genes and the concepts of their role in this mechanism. The first model, a simple one-dimensional model with two morphogens, which is a variant of Wolpert’s French flag model [1], describes the regulation of zone distribution along the SAM vertical axis. Despite a number of simplifications, this model has stationary solutions with biologically meaningful interpretation. The simplifying assumptions were successively abandoned in constructing a two-dimensional model of the mechanism underlying the regulation of SAM structure. This model provides a better understanding of the distributed system that regulates the SAM structure, and allows more detailed formalization of the modern concepts and experimental data concerning this mechanism.