ORCID
0000-0003-4680-1105
Date of Award
5-8-2024
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Rapid global climate change threatens food production and natural ecosystems. Knowledge of the mechanisms by which species adapt to local climates can inform future agriculture and conservation efforts and help to ensure sustainability and resilience of both cultivated and wild species. The overarching goal of this dissertation is to investigate the broad range of adaptive traits and their underlying genetics in wild populations of a widely distributed and polyploid forage plant, white clover. White clover is an ideal system because of its genetic diversity, widespread distribution, and its ability adapt to various environmental stresses through mechanisms that include its well-studied polymorphism for cyanogenesis (HCN release with tissue damage). These qualities make white clover a valuable model for understanding plant adaptation and agricultural sustainability in the face of climate change. In Chapter 1, I investigated whether the products of cyanogenesis can be recycled into primary metabolism, functioning as additional carbon and nitrogen sources. The gene expression data suggest that cyanogenic white clover can actively recycle the product of cyanogenesis (HCN) without herbivore-triggering reactions, supporting a beyond-herbivore-defense hypothesis. In Chapter 2, I documented the existence and the adaptive functions of copy number variations (CNVs) at the cyanogenesis loci in white clover based on a pangenome perspective. A key advance is de novo assembling a haplotype-phased genome and the integration of PacBio HiFi seq, Omni-C, linkage maps. Additionally, I documented the trajectory of karyotype evolution in the clover genus Trifolium and related genera in the “IRLC clade” of the legume family (Fabaceae). In Chapter 3, I investigated the contribution of the cyanogenesis polymorphism to the overall signatures of local adaptation in white clover. Utilizing landscape genomic approaches, I found that the cyanogenesis polymorphism is not one of the most significant features in local adaptation. Instead, phenological regulatory genes are likely to play some more important roles. In Chapter 4, I mapped the V locus and six modifier loci for the white leaf mark polymorphism in white clover, revealing a complex basis for this structure-based variegation. The apparent absence of compromised photosynthesis in variegated leaves suggests that factors other than simple fitness trade-offs may maintain this leaf mark polymorphism. In Chapter 5, I investigated the genetic mechanisms that underlie drought adaptation in white clover, and documented the relative contributions of cyanogenesis. I found that the cyanogenesis did not provide additional fitness benefits for white clover in drought-prone environments. Instead, the QTL mapping detected a locus showing antagonistic pleiotropy, at which the same allele could promote the flowering under drought but repress vegetative growth in water-sufficient environments.
Language
English (en)
Chair and Committee
Kenneth Olsen
Recommended Citation
Kuo, Wen-Hsi, "Understanding mechanisms of local adaptation in white clover (Trifolium repens L.): insights from a phenotypic cline and population genomics" (2024). Arts & Sciences Electronic Theses and Dissertations. 3033.
https://openscholarship.wustl.edu/art_sci_etds/3033