iSAM: Integrative Systems Analysis of the Shoot Apical Meristem

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Morphogenesis is the process by which organisms are built up from cells during development. Living organisms and their component organs have defined and recognisable shapes and forms, and this requires the coordinated actions of many cells. However, despite extensive focus on the cellular components, we still do not understand how such complex structures and patterns are produced. The goal of this project is to understand the morphogenetic events leading to growth and organ production in the shoot apical meristem (SAM) of higher plants, in an iterative process of analysis, model building, biological testing and refinement. The SAM is a population of dividing, undifferentiated cells that generates the leaves and other organs of plants in highly ordered patterns at shoot tips throughout the life of the plant. The SAM is a complex self-maintaining and stable structure, housing at its centre a population of stem cells and initiating organs on its periphery. The SAM produces the cells that comprise all aboveground plant tissues, and defines the number, type and position of lateral organs. SAMs are thus the basis of plant architecture and determinants of major agronomic traits. In view of its importance, the SAM has been extensively studied and a wealth of information is available concerning its molecular and cellular components. Nevertheless, we do not understand how these components assemble into the multicellular structures that have specific shapes and growth dynamics. It is this question we wish to address. We will do this through building multi-level computer models of SAM function, based on biological observation of living SAMs and measurements of key parameters, including responses to plant hormones that both define the growth and division of individual cells and coordinate the overall behaviour of the SAM structure. The outcome of the project will be a greatly increased understanding of the cellular basis of morphogenesis in the important SAM system. It will generate many relevant new data that will be organised in a database. This will underpin the first complete spatialised cellular model of SAM growth in the form of a growing virtual tissue, in which cells mechanically interact and respond according to a small network programme determining responses based on quantitative data. This model will be used for predictive experimentation allowing specific questions regarding the maintenance, organogenesis and morphogenesis of the SAM system to be addressed. This proposal links four leading research teams in UK, France and Finland, with a previous track record of several relevant joint collaborations, and bringing synergistic expertise and technologies in imaging, modelling, plant hormones and cell division to address this important systems problem.