Thesis

If you read my post “I’m back!” then you know that I recently finished my thesis. Now that it’s all safely submitted and I can’t make any more changes anyway, I wanted to post parts of the thesis for anyone who might be interested. Here, I’ll start off with the abstract, rationale, and organization scheme. In subsequent posts, I’ll have parts of the introduction and conclusion chapters.

Word cloud for the thesis (excluding citations and figure legends). I like how it looks like an ear of corn.

Abstract

Maize is a high yielding crop that provides a relatively high calorie source of food and feed, but focus on yield has not improved nutritional qualities. Some nutrients that are lacking in maize are iron and essential amino acids. In this dissertation some ways that genes from maize might be used to improve nutritional quality of maize are discussed, including improvement of bioavailable iron with maize globin and exploration of maize seed storage proteins. In addition, strategies to improve maize are explored, including breeding with mutations and transgenes and investigation of the effects of selection on transgenes.

Maize globin was found to be as bioavailable as ferrous sulfate, both when used as a forticant added to maize flour and when expressed in maize with an endosperm specific promoter. These results indicate that maize globin could be used to biofortify maize with highly bioavailable iron. Assessment of seed storage proteins in maize inbreds, landraces, and teosintes found unique proteins in teosintes that may be moved into maize through biotechnology or breeding to improve amino acid balance. Investigation of the effects of ensiling on seed storage proteins in maize used as ruminant feed found that longer ensiling times degraded some seed storage proteins, which may make the starch more digestible, but inoculation with Lactobacillus did not have an effect.

A variety of breeding methods can be used to improve qualities of maize. Maize transformed with a construct encoding green fluorescent protein controlled by a maize seed storage protein promoter was subjected to recurrent selection in order to increase transgene expression. This resulted in increased expression of the native gene with the same promoter, while unrelated traits were not changed. Backcrossing can be used to bring a mutation or transgene into a specific genetic background, while forward breeding can be used to improve characteristics of a line that carries a gene of interest.

Rationale

In many parts of the world, people are unable to obtain necessary nutrients from dietary sources. There are many factors that affect hunger and malnutrition, including political and social factors. Ideally, these factors will be changed to allow more people to lead healthy lives. Unfortunately, changing political and social systems can take decades, and in the meantime, many go hungry or malnourished. Maize is an important staple crop in parts of Africa, South America, and Central America. In addition, maize is an important feed crop in the developed and developing world. In this dissertation some ways that qualities of maize might be altered to help improve human quality of life are discussed, including improvement of bioavailable iron, amino acid balance, and investigation of effects of selection on transgenes.

Dissertation organization

This dissertation is divided into seven chapters. In the introductory chapter, an overall literature review is provided. The second chapter includes research conducted on maize hemoglobin. The goal of this research was to determine the potential of maize hemoglobin as an iron bioforticant. The third chapter includes research on transgene and native gene expression in response to selection for transgene expression. The goal of this research was to investigate the effects of selection on a transgene and to determine the relationship between expression of a transgene and a native gene with the same promoter. The fourth and fifth chapters are studies of seed storage proteins. The sixth chapter is about breeding with transgenes. In the seventh chapter, overall conclusions are discussed.

Note: Chapters four through six were previously published and were reprinted in my thesis with permission from the publishers. I doubt that permission extends to blog posts, so if you wish to see them and do not otherwise have access, please contact me directly. The citations for those chapters are as follows:

Flint-Garcia SA, Bodnar AL, Scott MP. Wide variability in kernel composition, seed characteristics, and zein profiles among diverse maize inbreds, landraces, and teosinte. Theoretical and Applied Genetics. 2009 Oct;119(6):1129-42. PMID: 19701625.

Hoffman PC, Esser NM, Shaver RD, Coblentz WK, Scott MP, Bodnar AL, Schmidt RJ, Charley RC. Influence of ensiling time and inoculation on alteration of the starch-protein matrix in high moisture corn. Journal of Dairy Science. 2010; 94(5):2465-2474.

Bodnar AL, Scott MP. Using mutations in corn breeding programs. The Handbook of Plant Mutation Screening. Ed. Meksem K, Kahl G. Wiley, 2010.

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