The angiosperms, or flowering plants, include organisms as familiar as daisies, poppies, roses and oaks, and are by far the most successful group of land plants. Prominent scientists and philosophers have wondered over centuries about how the amazing diversity of floral form came to be. To date, new tools in genomics and genetics are becoming available to help address these long-standing questions.
This project addresses the question of what are the genes underlying changes in flower morphology by focusing on "meadow rues" in the buttercup family having a variety of floral types. In order for flowers to produce seeds, they need to be pollinated. This means that pollen, the sperm bearing structure, needs to be transported to the female structures to achieve fertilization. This project will compare insect and wind pollinated flowers, investigating genes that are responsible for floral features that affect pollination. To this end, the investigator takes an interdisciplinary approach using microscopy and molecular biology to assess gene expression and function, and phylogenetics (building trees or genealogies of genes and species) to understand how these floral morphologies evolved and reveal the role of these particular genes in their evolution.
The principal investigator has worked extensively with undergraduates, mostly women and/or minorities, who will directly benefit as a result of this Award. She will teach undergraduate and graduate courses, including introductory biology course on campus with close to 400 students. A better understanding of the genetic basis of plant pollinator interactions has an impact on agriculture, since its manipulation can improve seed production. Characterization of the genes involved in making flower more attractive to insect pollinators has the added bonus of producing desirable traits for the floriculture industry.
The angiosperms, or flowering plants, include organisms as familiar as daisies, poppies, roses and oaks, and are by far the most successful group of land plants. Prominent scientists and philosophers have wondered over the centuries how the amazing diversity of floral form came to be. There is a growing consensus that the flower, a key innovation of the angiosperms, played a central role in this diversification by enabling co-evolution with animal pollinators. In times of DNA in the daily news and whole genomes being sequenced as we speak, new tools in the area of genetics have become available to help address these long-standing question. This project addressed the question of what are the genes underlying changes in flower morphology by focusing on "meadow rues" (genus Thalictrum), in the buttercup family Ranunculaceae, which include a variety of floral types. In order for flowers to produce seed, they need to be pollinated: pollen, the sperm-bearing generation, needs to be transported to the female structures to achieve fertilization, resulting in fruits and seed. This project compared insect and wind-pollinated flowers, investigating a gene responsible for a floral feature that affects pollination. To this end, we took an interdisciplinary approach using microscopy, molecular biology to assess gene expression and function and phylogenetics (building trees or genealogies of genes and species) to understand how these floral morphologies evolved and what are their genetic underpinnings. Flowers of Thalictrum are apetalous, yet different flower organs (sepals or stamens) have adopted petaloid appearance, becoming attractive to insect pollinators. My team has investigated the genetic basis of conical cells, a micro-morphological marker of petaloidy that affects pollinator attraction. Raised epidermal cells contribute to the perceived color intensity and brightness of flowers by pollinators (Fig. 1). As a result of this work, we have identified a gene involved in a trait that likely contributes to flower diversity. Subsequently we silenced the candidate gene using Virus Induced Gene Silencing in a species with petaloid sepals and one with petaloid stamens. These targeted gene-silencing experiments resulted in flattening of conical cells in sepals, stamens and stigmas (Fig. 2). We conclude that this gene has been co-opted to produce conical cells that impart "showiness" to sepals or stamens in the absence of true petals. Moreover, we showed for the first time a role of this gene in stigmatic papillae, the area of the female reproductive organ where pollen lands and germinates to achieve fertilization. Given that stigmas from wind-pollinated species are much longer and have many more stigmatic papillae than stigmas from insect-pollinated species (Fig. 3), this gene must have played a central role during the evolution of wind pollination from insect-pollinated ancestors. The principal investigator has worked extensively with undergraduates, mostly women and/or minorities, three undergraduate students, one high-school students, one graduate student and one post-doc directly benefited as a result of this proposal. She teaches undergraduate and graduate courses, including the biggest introductory biology course on campus, serving 400-700 students each quarter, most of them pre-meds. A better understanding of the genetic basis of pollinator attraction by flowers has an impact on agriculture, since its manipulation can improve seed production. The isolation and characterization of the genes involved in making flowers more attractive to insect pollinators has the added bonus of producing desirable traits for the floriculture industry.
