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Because plants are sessile and can’t escape from predators, many plant species have evolved exquisite defensive systems, ranging from chemical defenses to physical deterrents. Thorns, prickles, and spines all act as weapons against herbivores, but each arises from a distinct developmental origin. Unlike prickles or spines, thorns arise from axillary shoot apical meristems that proliferate for a time and then terminally differentiate into a sharp hard tip. Like other meristems, thorn meristems contain stem cells but, in the case of thorns, these stem cells undergo a programmed cessation of proliferative activity. As such, thorns represent a fascinating variation on how stem cells are regulated. Since most citrus species have thorns, we have focused our attention on this genus. We have characterized a gene network necessary for thorn development, and by disrupting this pathway, we can generate plants that have many more branches and so alter plant architecture. Not only has this work illuminated some of the molecular mechanisms controlling thorn development, but the methods we have developed have allowed us to tackle some of the challenges facing citrus agriculture today.
Vivian Irish is the Eaton Professor of Molecular, Cellular and Developmental Biology, and Professor of Ecology and Evolutionary Biology, at Yale University. As a graduate student at Harvard University, she focused on characterizing the developmental genetic mechanisms specifying dorsal-ventral polarity in Drosophila. She continued to pursue these interests in patterning processes as a Jane Coffin Childs postdoctoral fellow at the University of Cambridge. As a National Science Foundation postdoctoral fellow at Yale University, she turned her attention to exploring the specification of floral organ types. Now a faculty member at Yale, her research centers on understanding mechanisms controlling flower development using a variety of molecular, biochemical, and genetic approaches. She has also long been interested in the evolution of developmental mechanisms with a specific focus on the diversification of gene regulatory networks controlling flower development and stem cell activity. She is also interested in the biotechnological applications of her work to crop production and agriculture. Irish has held several administrative roles at Yale, including Chair of the Department of Molecular, Cellular, and Developmental Biology, and Director of Undergraduate Studies in Biology. She is an elected member of the Connecticut Society of Science and Engineering. Irish is also a past-president of the Society for Developmental Biology and was a visiting professor at the École Normale Supérieure, Lyon, France.