Developmental Genetics of Corolla Tube Formation: A Key Morphological Innovation During Angiosperm Evolution

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About one third of the ~300,000 flowering plant species (e.g., petunia, snapdragon, primrose, rhododendron) produce flowers with petals fused into a tubular structure referred to as the corolla tube. The corolla tube encloses and protects the nectaries and reproductive organs. Differences in the length, width, and curvature of the corolla tube have led to an endless variety of differently shaped flowers that attract specialized groups of pollinators (e.g., beeflies, hawkmoths, hummingbirds, nectar bats). Because of its importance in plant reproduction, the corolla tube is considered a key morphological innovation that contributes to plant diversification and speciation. This study employs a new genetic model system, monkeyflowers (Mimulus lewisii), to identify and characterize the genes responsible for corolla tube development, including the genes responsible for coordinated organ fusion and the generation of a diversity of corolla tube shape. The flower images, pollination videos, and interactive, multimedia illustrations resulting from this project will be incorporated into a new Plant Biology section on the nationally and internationally recognized Learn.Genetics website as online educational resources for K-16 students. Multi-disciplinary training in genetics, development, and evolution includes post-doctoral associates, graduate students and undergraduate students, including members of under-represented groups enrolled in the McNair Scholars Program at UConn.This study leverages recently developed genomic resources, stable transgenic tools, and chemically induced mutants of monkeyflowers (Mimulus) to identify and characterize genes that control corolla tube formation. Results from preliminary work in the investigator's laboratory allows the formulation of a new conceptual model for the developmental genetic control of corolla tube formation. At the heart of the model is auxin signaling that mediates coordinated growth between the bases of the initially separate petal primordia and the inter-primordial regions. Upstream of this core module is the genetic regulatory network (GRN) controlling lateral expansion of the petal primordia, essentially the same GRN that controls leaf adaxial/abaxial polarity and lamina growth. Downstream of this core module lie the organ boundary genes that suppress localized tissue growth if not repressed by auxin signaling. Two specific aims will be pursued to test these hypotheses: (i) Determine the functional roles of the major regulators of leaf polarity in corolla tube formation using in situ hybridization, ectopic gene expression, and RNA interference in the model species Mimulus lewisii. (ii) Identify additional components of the GRN controlling corolla tube formation by bulk segregant analyses of several additional non-allelic mutants of M. lewisii with unfused corollas. Genetic interactions among the newly identified genes and the known leaf polarity regulators will be determined by generating double or higher order combinatorial mutants and transgenic lines. RNA-Seq analyses of selected regulatory mutants and transgenic lines of the leaf polarity regulators will be conducted to identify downstream genes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.