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Forrester, Nicole (2019) EXPLORING HOW POLYPLOIDY ENHANCES A PLANT-BACTERIAL MUTUALISM. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Polyploidy (i.e., the possession of more than two complete sets of chromosomes) is a major driver of ecological and evolutionary processes in plants. Previous work has illuminated how polyploidy affects genotypes, phenotypes, and abiotic interactions, yet little is known about how it alters plant-biotic interactions. The legume-rhizobia symbiosis is a model interaction between plants and mutualistic microbes, in which rhizobia bacteria fix nitrogen in exchange for carbon provided by plant hosts. This mutualism regulates global nutrient cycles and plays a prominent role in the distribution and diversification of legume taxa. Despite the widespread importance of this mutualism, it remains unclear how polyploidy affects mutualism traits and host benefits from it. To address this fundamental gap in knowledge, I developed a framework of mechanistic hypotheses for how plant polyploidy might directly enhance the quantity and quality of rhizobial symbionts hosted, subsequently improving plant growth benefits. I tested mechanisms within this framework using stabilized polyploids of Medicago sativa by asking whether polyploids exhibited greater niche breadth, increased host benefits, and reduced fitness plasticity across a broad range of Sinorhizobium symbionts relative to diploids. Finally, to isolate the direct effects of plant polyploidy on the legume-rhizobia mutualism, I created synthetic neotetraploid M. sativa plants and compared them to their diploid progenitors. Using confocal microscopy, I quantified the direct effects of plant polyploidy on the internal structure of mature root nodules. These studies reveal that polyploid plants obtain greater benefits from rhizobial symbionts and maintain them across a broad range of rhizobial symbionts relative to diploid plants, which may be due to direct changes in internal nodule structure. Overall, this dissertation uncovers novel patterns and underlying mechanisms for how plant polyploidy alters a model species interaction, and in doing so, contributes to ecological and evolutionary theories concerning the widespread success of polyploid plants.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Forrester, Nicolenjf26@pitt.edunjf260000-0002-5210-8801
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairAshman, Tia-Lynntia1@pitt.edutia1
Committee MemberCarson, Walterwalt@pitt.eduwalt
Committee MemberLawrence, Jeffreyjlawrenc@pitt.edujlawrenc
Committee MemberRichards-Zawacki, Corinnecori.zawacki@pitt.educori.zawacki
Committee MemberSachs,
Date: 20 June 2019
Date Type: Publication
Defense Date: 21 March 2019
Approval Date: 20 June 2019
Submission Date: 28 March 2019
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 102
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Biological Sciences
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: bacteria, legume, plant, polyploidy, mutualism, rhizobia
Date Deposited: 20 Jun 2019 15:31
Last Modified: 20 Jun 2019 15:31


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