Evolution of Vegetative Phase Change in the Acacieae

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This proposal explores the evolution of vegetative phase change in the Acacieae, a large, drought-resistant, tribe of nitrogen-fixing legumes. This group includes genera that produce only bipinnately compound leaves, and a more recently evolved genus (Acacia) that initially produces compound leaves, but then switches to the production of a simple leaf called a phyllode. Nested within Acacia is a group of approximately 70 species (Botrycephalae) that produce only compound leaves. It has long been assumed that these species represent derived ?juvenilized? forms of phyllodinous species, but there is no evidence for this conclusion. The juvenile phase of vegetative development is specified by high levels of the miRNAs, miR156 and miR157. The working hypothesis of this project is that the Botrycephalae arose from phyllodinous species by the prolonged, high expression of miR156 and/or miR157. To obtain preliminary evidence for or against this hypothesis, the expression of the mature miR156/miR157 transcripts will be examined in a few phyllodinous and bi-pinnate species of Acacia, using Northern analysis. The genes that encode miR156/miR157 will be identified by next-generation sequencing genomic DNA from a representative phyllodinous and bi-pinnate species. This will make it possible to test the feasibility of examining the expression of specific miR156/mIR157 genes by qRT-PCR. The results of these experiments will provide the ?proof-of-concept? for a future proposal aimed at determining the molecular basis for variation in the expression of juvenile and adult traits in the Acacieae. Broader ImpactAn exhibit on phase change will be created for annual Philadelphia Science Carnival, held on the Ben Franklin Parkway. The goal of this exhibit will be to teach the many children who attend this carnival that plants are dynamic, and change as they grow. Attendees will be asked to find all the differences between juvenile and adult ivy and corn leaves, and will be introduced to phase change in Acacia and Eucalyptus. Arabidopsis plants transformed with 35S::miR156 will be used to illustrate how a single gene can change the entire architecture of the shoot.