Plastid Genome Evolution in the Parasitic Genera Cuscuta (Convolvulaceae) and Krameria (Krameriaceae)

Almost all plants are primary producers and many of their phenotypic and genotypic features are centered on the ability to conduct photosynthesis. Variation in these features is rare across green plants due to the degree of selective pressure imposed by primary production. This is particularly true for plastid genomes (plastomes) given that chloroplasts are the primary site of photosynthesis in the cell and that plastomes encode key portions of the photosynthetic apparatus.In only a handful of embryophyte lineages, however, a heterotrophic lifestyle has evolved and reliance on photosynthesis for resource acquisition is reduced or completely absent. In these plants, the selective pressure imposed by primary production is lifted and previously conserved features are able to evolve more freely, including the plastid genome. The genus Cuscuta is one such lineage. It contains c. 200 obligate branch parasite species, diverse in terms of the degree of their heterotrophy: some can conduct limited photosynthesis whilst others are entirely nonphotosynthetic. In chapters 2-4, I assembled and analyzed plastomes from each section of Cuscuta in order to comprehensively characterize the patterns in their evolution across the genus. I found that most species retain the bulk of their photosynthesis genes and, therefore, at least some aspect of the bioenergetic pathway remains available for them to use. In plants forming two clades within Cuscuta, however, there was a wholesale loss of plastid genes encoding the photosynthetic machinery. The genus Krameria contains 18 species of root hemiparasites and they, like Cuscuta, represent an additional independent transition from autotrophy to heterotrophy. In chapter 5, I assembled the plastid genome of one Krameria species and analyzed it along with two previously reported plastid genomes from the group. I found that these species exhibit sweeping retention of plastid genes, unprecedented amongst parasitic angiosperms, and do not appear to have been impacted by the transition to heterotrophy the same way that other parasitic lineages have been. By characterizing plastomes in these two genera, my thesis contributes to our growing understanding of how heterotrophic plants, and genomes, change due to a reduction (or complete loss) of the selective pressure imposed by photosynthesis.

Department dc:contributor.department

Ecology and Evolutionary Biology

Year dc:date.issued

2022

Author dc:creator

• Banerjee, Arjan

Advisor dc:contributor.advisor

• Stefanović, Saša

• Convolvulaceae
• Cuscuta
• Heterotroph
• Parasite
• Plastid
• Plastome

Statement dc:rights

• Attribution 4.0 International

Licence dc:rights.uri

• http://creativecommons.org/licenses/by/4.0/

Handle dc:identifier.uri

http://hdl.handle.net/1807/123479

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/123479