GETTING TO THE ROOT CAUSE: THE GENETIC UNDERPINNINGS OF ROOT SYSTEM ARCHITECTURE AND RHIZODEPOSITION IN SORGHUM

Author

Farren Smith, West Virginia UniversityFollow

Semester

Summer

Date of Graduation

2022

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Biology

Committee Chair

Jennifer Hawkins

Committee Co-Chair

Jonathan Cumming

Committee Member

Jonathan Cumming

Committee Member

Edward Brzostek

Abstract

Plants are some of the most diverse organisms on earth, consisting of more than 350,000 different species. To understand the underlying processes that contributed to plant diversification, it is fundamental to identify the genetic and genomic components that facilitated various adaptations over evolutionary history. Most studies to date have focused on the underlying controls of above-ground traits such as grain and vegetation; however, little is known about the “hidden half” of plants. Root systems comprise half of the total plant structure and provide vital functions such as anchorage, resource acquisition, and storage of energy reserves. The execution of these key functions via root system architecture and root exudation directly determines plant performance, and thus reproductive fitness. Despite the significance of roots, the genetic controls contributing to their variation have gone understudied due to the technical difficulties associated with below-ground phenotyping.

Domesticated plants provide an excellent framework for studying the genomic underpinnings of phenotypic diversity due to the telescoped evolutionary time frame under which artificial selection took place. The rapid evolution of domesticates from their extant antecedent affords direct observations of derived traits and their underlying genetic controls. Sorghum, a globally important domesticated grass species with a small diploid genome, few genetic repeats, and a wide variety of adaptations, serves as a good model for studying selection during domestication. Domesticated S. bicolor is an annual accession with large seeds and flowering organs compared to its wild relative, S. propinquum. Comparatively, S. propinquum is perennial with dense rhizomes and small flowering panicles. Due to their distinctly opposing root systems, a recombinant inbred line (RIL) population formed from a cross between S. bicolor and S. propinquum was used to identify the specific root morphological and metabolic adaptations that derived from domestication. The RIL population was phenotyped using high-throughput image analysis to locate the underlying genomic factors controlling derived traits via high-density Quantitative Trait Loci (QTL) mapping. Nine novel QTL influencing root morphology were identified. No QTL were identified for metabolic exudation; however, crown root growing angle was found to be a statistically significant predictor of the percentage of carbon and nitrogen in the rhizosphere. The relationship between steep growing angles and increased rhizosphere carbon and nitrogen suggests that increased exudation was derived during domestication. Candidate genes and pathways were identified including those that encode meristem transcription factors, plant hormone receptors, and actin trafficking. These findings advance our understanding of the underlying genomic factors controlling root system architecture (RSA) and root exudation that were selected during the domestication of Sorghum. The results of this study can be integrated into breeding programs for the establishment of elite root lines used to mitigate the effects of current and future environmental challenges of croplands in a sustainable manner.

Recommended Citation

Smith, Farren, "GETTING TO THE ROOT CAUSE: THE GENETIC UNDERPINNINGS OF ROOT SYSTEM ARCHITECTURE AND RHIZODEPOSITION IN SORGHUM" (2022). Graduate Theses, Dissertations, and Problem Reports. 11438.
https://researchrepository.wvu.edu/etd/11438