Semester

Spring

Date of Graduation

2013

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Biology

Committee Chair

DiFazio, Stephen P.

Committee Co-Chair

Carina Barth

Committee Member

Jonathan R. Cumming

Committee Member

James B. McGraw

Committee Member

Dorothy Vesper

Abstract

Cadmium (Cd), a known carcinogen and one of the leading heavy metal pollutants on a global scale, is released to the atmosphere through various industrial processes such as smelting and mining and other applications including manufacture of batteries and phosphate fertilizers. It causes many deleterious effects in plants, and is harmful to humans through its entry into the food chain. Traditional methods of remediating Cd-contaminated soils, such as excavation and land-filling, are expensive and disturb the natural topography. The emerging method of phytoremediation in which plants are employed to remediate contaminated soils has become increasingly popular because of its cost effectiveness and environmentally friendly characteristics. Populus trees have been extensively studied for their effectiveness in phytoremediation due to their size, productivity, and status as a model organism. My dissertation had the following objectives with the ultimate focus on developing transgenic Populus trees for phytoremediation of Cd contaminated soils: 1.) Map QTL (Quantitative Trait Loci) for Cd tolerance and identify candidate genes for Cd tolerance from QTL intervals, microarray studies and comparative genomics in Populus; 2.) Map QTL for growth, biomass and phenology traits in Populus under greenhouse and field conditions; 3.) Study the influence of Fe on Cd toxicity effects on growth and biomass traits of Cd tolerant and Cd susceptible Populus genotypes. In Chapter 2, I conducted a greenhouse hydroponic study in which 252 genotypes of a pseudobackcross Populus progeny of family 52-124 were grown and treated with Cd. The phenotypic data recorded on these genotypes were used to identify tolerant and susceptible genotypes, and also for identifying QTL for Cd tolerance. The individuals used in the hydroponic experiment were scored for SNP (Single Nucleotide Polymorphism) markers, and statistical associations were detected between the phenotypic and genotypic data, indicating the presence of QTL. Candidate genes were identified from these QTL intervals using microarray studies and comparative genomic approaches. The same pedigree was grown in a field trial at West Virginia University Agronomy Farm and extensive phenotypic data was recorded on growth, biomass and phenology traits during 2008 and 2009 seasons. In Chapter 3, I compared biomass and phenology trait QTLs across the above hydroponic experiment and from the field study. Extensive phenotypic variation was observed among the growth and biomass traits in both the studies and the change in the QTL positions across experiments and across years suggested changing genetic control on the traits. For Chapter 4, a greenhouse hydroponic experiment was carried out in which a Cd tolerant and a Cd susceptible Populus genotype were studied. This experiment was a dosage study with two levels (0 muM and 25 muM) of Cd and two (0 and 100 muM) levels of Fe. All of the treated plants were examined for Cd toxicity effects under high Fe and Fe deficiency conditions on growth and biomass traits. This experiment demonstrated that high Fe conditions mitigated the toxic effects of Cd, and that this effect was more pronounced in the Cd susceptible genotype than in the Cd tolerant genotype. In the future, the candidate genes identified from these studies will be functionally characterized using transgenic approaches and tested for their production and phytoremediation capabilities under greenhouse and field trials. My research has therefore laid the groundwork for the improvement of Populus as a crop for biofuels production and phytoremediation.

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