Abstract
Author SummaryHow the regulation of cell division contributes to cell patterning in an organ is an important question in developmental biology. We chose to study cell size patterning in the Arabidopsis sepal, the green leaf-like floral organ, because it contains a wide range of cell sizes—from giant cells to small cells—and because sepals, as the outermost floral organ, are accessible for live cell imaging. In this study we image the early development of living sepals and follow each of the cell divisions to determine how cells of different sizes are created. We observe that the times when cells divide and when they stop dividing are highly variable. Using computational modeling, we then show that a model in which these decisions are made randomly with the probabilities we observed in vivo can recapitulate the production of the range of cell sizes seen in the living sepal. We also show that changing these probabilities within our model robustly predicts the novel cell patterns observed in mutant plants with altered cell division timing. We conclude that probabilistic decisions of individual cells—rather than deterministic, organ-wide mechanisms—can produce a characteristic and robust cell size pattern in development.
Highlights
During development, complex patterns of specialized cell types emerge de novo
One system for investigating this problem is the development of the Arabidopsis sepal epidermis, which forms a characteristic cell size pattern ranging from giant cells stretching one fifth the length of the sepal to small cells stretching one hundredth the length of the sepal (Figure 1A–C; giant cells marked in red)
How the regulation of cell division contributes to cell patterning in an organ is an important question in developmental biology
Summary
Complex patterns of specialized cell types emerge de novo. Pattern formation occurs in a changing environment where cells proliferate and differentiate, and we are interested in how regulation of cell division contributes to the patterning of an organ [1]. One system for investigating this problem is the development of the Arabidopsis sepal epidermis, which forms a characteristic cell size pattern ranging from giant cells stretching one fifth the length of the sepal to small cells stretching one hundredth the length of the sepal (Figure 1A–C; giant cells marked in red). The sepal is the outermost, green, leaflike floral organ, which acts defensively to enclose and protect the developing reproductive structures. Sepals are unique in containing such a pattern of diverse cell sizes and giant cells have been used as a marker for sepal organ identity [3,4,5,6]. A similar cell size pattern containing giant cells is found in the Arabidopsis leaf epidermis (Figure S2H) [7]
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