In plants, the leaf epidermis is an important architectural control element that defines the growth properties of underlying tissues and the overall form of the organ. The size and shape of leaves are important traits in agricultural production, as is the architecture of the leaf. Therefore, a deep understanding of the genetic and cellular control of leaf development is an important research goal. The tissue-level behavior of the epidermis is driven by the polarized growth of jig-saw-puzzle shaped pavement cells with interdigitating lobes. However, the molecular, cellular, and mechanical control mechanisms for this important cell shape control pathway are not known. This knowledge gap cannot be filled until new experimental and computational approaches are developed. The objective of this project is to create a new set of image analysis techniques, mechanical devices, and mathematical models that will enable a mechanistic understanding of how tissue-level mechanical forces interact with intracellular signaling pathways to control the geometry of morphogenesis. Our approach will include the development of new image analysis and nano-scale mechanical devices that will enable quantitative tests for the mechanisms of pavement cell growth. We will create computational models that will allow us to analyze the plausibility of existing growth control models, and make new predictions about how mechanical forces and intracellular reorganization interact to control cell shape. The research will include interdisciplinary cross-training of the research team, and is expected to generate technical advances in image processing and analysis that will be made publicly available through a collaboration with the iPlant data sharing resource. The project will generate broadly useful computational models that simulate plant cell growth control mechanisms and generate predictions that can be experimentally tested. This project is jointly supported by the Programs in Plant, Fungal and Microbial Development in the Division of Integrative Organismal Systems and by the Networks and Regulation and Cellular Processes Programs in the Division of Molecular and Cellular Biosciences.
The size, shape, and number of leaves are important agricultural traits that determine the efficiency with which the plant can capture photosynthetically active light. The outer layer of the leaf termed the epidermis exerts a major influence on the size and shape of the organ. However, the mechanism by which the growth properties of individual cells dictate tissue- and organ-level growth properties are not known. This lack of knowledge greatly limits our ability to manipulate this important crop trait strategically. The primary goal of this award was to create a new set of experimental and computational tools to analyze the mechanisms of plant cell shape change. Our interdisciplinary team successfully created a new computer program called Lobefinder, which can accurately quantify the morphology of jig-saw-puzzle shaped leaf epidermal cells over time. This tool enables one to analyze gene function objectively in the context of polarized growth. Our group created a series of long-term time lapse imaging tools that allows one to quantitatively measure the subcellular dynamics of growth. These experiments allowed our team to create a plausible computational finite element model that describes the physical features of a plant cell wall that are needed to generate a polarized growth response. This work provides the proof of concept, in which one can genetically manipulate an intracellular protein to control the physical properties of the cell wall and the growth properties of cells. This award supported intersiciplinary research in engineering, math, and plant biology. The award provided cutting-edge training for one post-doctoral fellow and one graduate student. The research results were presented in oral seminars at four national meetings, and are in preparation for publication.
