The Origin and Evolution of Flower Characters in Angiosperms with a Case Study on the Genetic Basis of Zygomorphic Corolla Development in Bee and Hummingbird Pollinated Species of Schizanthus (Solanaceae)
Doctor of Philosophy
Integrative Life Sciences
Dr. Wenheng Zhang
This Ph.D. dissertation investigates two main projects separated into two chapters, one for each. The first chapter explores the evolution of flowering plants (angiosperms), a macro-scale study. The second project is on a micro-scale that focus on exploring the genes that regulate the similarities and the differences of flower morphology reflecting their different pollination syndromes in two species of Schizanthus (Solanaceae), i.e., S. pinnatus, a bee-pollinated flower, and S. grahamii, a hummingbird- pollinated flower.
In the first chapter, I used floral diagrams to study the origin and the evolution of floral traits in angiosperms, a new set of morphological data to investigate such an important question. We have to understand the origin and evolution of flower morphology to understand angiosperm’s evolutionary success. The primitive flowers’ characters have been a mystery, and many studies have already investigated their traits, e.g., merosity, phyllotaxy, and symmetry, in a phylogenetic framework. Our research confirmed or conflicted with their results and characterized new flower traits that have never been highlighted before, such as the evolution of the bract. Besides the primitive flower’s features, we also investigate the evolution of floral characteristics in extant angiosperms, focusing on exploring whether the presence of bract influences floral symmetry evolution using a phylogenetic approach.
In the second chapter, I investigated the genetic bases of flower morphology of Schizanthus (Solanaceae). The strongly zygomorphic flowers of Schizanthus are adapted to pollination by bees, hummingbirds, and moths. Specifically, we investigated the genetic basis of the distinct zygomorphic corollas in S. pinnatus and S. grahamii using differential gene expression (DGE) profiles by sequencing the RNA transcriptomes. Also, we identified genes that were differentially expressed in the corolla and androecium between the two species. We discussed the implications of differentially expressed genes across the plane of floral symmetry and their potential role in developing floral morphology associated with distinct pollination syndromes. Furthermore, we assigned the enriched differentially expressed genes to specific Gene Ontology (GO) terms, for which each term includes many genes. Each GO term is described in a meaningful biological concept. The genes included are the candidate genes likely responsible for regulating the distinct flower morphology in each species.
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Available for download on Tuesday, December 09, 2025