ORCID

https://orcid.org/0009-0001-4642-0575

Date of Award

2025

Document Type

Dissertation

Department

Biological Sciences

First Advisor

Dianella G Howarth

Second Advisor

Javier F Juarez

Third Advisor

Xue Mei

Abstract

Shifts between radial symmetry (actinomorphy) and bilateral symmetry (zygomorphy) in flowers have occurred multiple times independently within angiosperms (flowering plants). Evidence across angiosperms indicate the transcription factors RADIALIS (RAD), DIVARICATA (DIV), and CYCLOIDEA (CYC) play a major role in regulating floral symmetry and morphology. The CYC-like genes have been shown to shift their expression dorsally independently in nearly all shifts to bilaterally symmetrical flowers examined. Three core eudicot clades of CYC-like genes have been identified: CYC1, CYC2 and CYC3, with only CYC2 genes being shown to have a role in floral symmetry. We use the non-model plant, Fedia graciliflora (Caprifoliaceae) to examine the effect of CYC2 as well as CYC3 paralogs on floral shape and symmetry. F. graciliflora has strongly bilaterally symmetrical flowers with morphologically distinct dorsal (upper), lateral, and ventral (lower) petals and only two functional stamens. Fedia is nested within the Valerianella, a group with pseudo-radially symmetric flowers with three functional stamens, providing a model for studying the evolution of strong bilateral symmetry and teasing apart the effects from each paralog. Here we used Virus-Induced Gene Silencing (VIGS) to knockdown each of the paralogs separately: FgCYC2A, FgCYC2B, FgCYC3A, and FgCYC3B. The down-regulated plants were assayed using geometric morphometrics combined with tools of multivariate statistical shape analysis to quantify shape changes, using a combination of landmarks and semilandmarks to precisely capture in high detail the corolla outline. Using canonical variate analysis (CVA), we are able to statistically model the morphological effect of lower expression of each paralog. These analyses indicate that each paralog plays a slightly different role in patterning floral symmetry, both in location and size of petal lobes. Additionally, here we show evidence for the first time that CYC3, despite having lower expression in general, also patterns corolla shape. Using these gene knockdowns, we will investigate the effects the downregulation of each of the four CYC paralogs has on FgRAD2 and FgDIV1 genes in Fedia graciliflora as well as other double gene knockdown combinations.

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