Collaborative Research: Conservation and Diversification of Regulatory Pathways Controlling Stem Cell Proliferation

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Stem cells undergo self-renewal to produce more stem cells, as well as producing daughters that go on to produce multiple specialized cell types. In plants, cells of the shoot apical meristem (SAM) act as stem cells, giving rise to more stem cells as well as specialized cell types contributing to the leaves, branches and fruit. This study investigates the basis for thorn development in Citrus as a means to understand how the termination of stem cell proliferation is controlled. Thorns arise from SAM cells that fail to self-renew, and instead terminally differentiate, providing a unique opportunity to explore how SAM cell proliferation is controlled. Citrus is an excellent study system to explore this question as many Citrus species possess thorns, and multiple genetic and genomic tools exist for work with Citrus. In this study, candidate genes from Citrus that have been implicated in regulating stem cell proliferation will be examined for their roles in thorn development using expression analyses and employing newly developed transgenic approaches. In a complementary set of experiments, key genes involved in the arrest of stem cell proliferation will be identified via genome-wide comparisons of the transcriptomes of thorned vs. thornless Citrus species. These analyses will begin to define the processes important for stem cell arrest, as well as elucidating conserved and novel mechanisms of stem cell maintenance and differentiation. Citrus plant growth, fruit yield and harvest costs are all affected by thorniness, and so understanding how to manipulate thorn production will greatly impact the economics of this valuable fruit crop. A postdoctoral associate, a graduate student and three undergraduates will receive training as a part of this project. Inaddition, a display of Citrus biology will be mounted at the Marsh Botanical Gardens, NewHaven, CT, aimed at promoting public awareness and understanding of science.