Access Type

Open Access Thesis

Date of Award

January 2014

Degree Type

Thesis

Degree Name

M.S.

Department

Biological Sciences

First Advisor

Edward M. Golenberg

Abstract

Sexual dimorphism in domesticated spinach, Spinacia oleracea, is thought to be determined by differential expression of floral organ identity genes. We examined the floral organ morphologies of seven species in the Chenopodiaceae, including two wild species of spinach, in order to gain insight into the evolution of floral reproductive strategy in this clade. The species within the Anserineae demonstrate extensive evolution in floral morphology and reproductive strategy, and Spinacia is unique for having been domesticated rather recently and for being dioecious. We found C. album to be hermaphroditic, C. foliosum and M. nuttalliana to be gynomonoecious, while C. bonus-henricus exhibits protogyny. For each species and cultivar examined, we isolated sequences for the genes UNUSUAL FLORAL ORGANS (UFO), AGAMOUS (AG), APETALA3 (AP3), PISTILLATA (PI) and for the gene coding for the small subunit of the RuBisCO complex (RBCS), which is involved in carbon fixation during photosynthesis. We also analyzed published sequences for the chloroplast genes RBCL and MATK. The RBCS, MATK, UFO, AG, AP3, and PI genes reveal a consistent phylogeny that most likely represents the true organismal phylogeny for these species, providing key insights into the evolution of reproductive strategy in this tribe. Phylogenetic analysis of the RBCL gene shows Spinacia as sister to M. nuttalliana, and placing C. album within a cluster with C. bonus-henricus and C. foliosum. This tree topology deviates from those generated from TRNL-F /ITS data as well as all others generated in this study. All of these other gene analyses consistently give Spinacia as sister to a clade that includes C. bonus-henricus, C. foliosum, and M. nuttalliana, recently recognized as the genus Blitum. We demonstrate evidence for increased rates of nucleotide substitutions in Spinacia, though there is no molecular evidence for domestication or positive selection. Our findings indicate that sequence evolution in this tribe is being driven mostly by insertion/deletion mutations for the genes sampled, and show that Spinacia has a unique combination of mutations in the coding regions of the floral identity genes AP3 and PI. We also describe unique polymorphisms in a hypervariable region of the UFO gene that are unique to Spinacia.

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