ABR: Genes controlling Fruit development in Arabidopsis

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The fruit is arguably the most complex plant organ and serves to protect the seeds as they develop and then disperse them at maturity. Fruits from diverse plant species come in a wide array of shapes and sizes, and only recently have a number of the genes that pattern the fruit been identified. The ovary of the Arabidopsis fruit consists of three main regions: the valves, which are derived from the ovary walls, the replum, which is the structure that remains after the valves have detached at fruit maturity, and the valve margins that form at the valve/replum boundaries. The valve margin is essential for seed dispersal and consists of two main pattern elements. The first is a cell separation layer, where separation of cells allows the valves to detach from the replum during the seed dispersal process. The second element of the valve margin is the lignified layer that is also proposed to promote seed dispersal at fruit maturity. Valve margin formation requires the activities of the SHATTERPROOF MADS-box transcription factors as well as the INDEHISCENT and ALCATRAZ basic helix-loop-helix type transcription factors. The FRUITFULL MADS-box transcription factor specifies the valves in large part by negatively regulating the valve margin identity genes. Similarly, the REPLUMLESS homeodomain transcription factor specifies the replum in large part by negatively regulating the valve margin identity genes. Although we now have a handle on the major regulators that pattern the Arabidopsis fruit, we still know relatively little about how specific cell types within fruits are specified. A major focus of our proposed studies is to dissect the cascade of gene activity that leads to differentiation of specific cell types during fruit development. We propose a multi-pronged approach to achieve these goals. We will continue our genetic studies by performing enhancer and suppressor screens of existing mutants with the longer-term goal of cloning the corresponding genes. We will perform microarrray experiments to identify targets of the fruit patterning genes. We will characterize the role of plant hormones in specifying fruit patterning and cellular differentiation. Together, these and other proposed studies will allow us to begin to dissect the cascade of gene activity that leads to cellular differentiation during fruit development.