Biochemical and genetic analysis of factors influencing lysine content in maize (Zea mays L.) endosperm
AdvisorLarkins, Brian A.
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PublisherThe University of Arizona.
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AbstractProtein-bound and free lysine contributed to the total lysine content of maize endosperm, and both of these can be significantly increased by the opaque-2 (o2) mutation. Elongation factor 1A is one of the lysine-rich proteins increased in o2 mutants, and its concentration is highly correlated with the protein-bound lysine content of the endosperm. However, the biological basis of this correlation is unknown. The mechanism by which the free amino acid content, including free lysine, is increased by the o2 mutation is also poorly understood. Understanding the biological basis of these traits could provide new insights for improving maize nutritional quality. A maize genetic linkage map consisting of 83 DNA simple sequence repeat markers was created for two inbred lines (Oh51Ao2 and Oh545o2) that differ in elongation factor 1A and free amino acid content. Quantitative trait locus analysis was performed and identified two significant loci that accounted for 25% of the variance for elongation factor 1A content. One of them was linked with a cluster of 22-kD α-zein genes on the short arm of chromosome 4; the other locus was on the long arm of chromosome 7 and may be linked to the 27-kD γ-zein genes. Quantification of protein and mRNA levels of the major storage proteins suggested that a higher level of α-zein gene expression co-segregates with higher elongation factor 1A content. Furthermore, measurement of protein body size and density predicted a greater protein body surface area (80% higher) in Oh51Ao2 than Oh545o2, and this may partially explain the higher level of elongation factor 1A in Oh51 Ao2 by creating a more extensive cytoskeletal network. Quantitative trait locus analysis of free amino acid content identified four loci accounting for about 46% of the variation for this trait. One locus on the long arm of chromosome 2 is tightly linked to monofunctional aspartate kinase and a bifunctional aspartate kinase-homoserine dehydrogenase gene. Biochemical characterization of these enzymes indicated the aspartate kinase in Oh545o2 is less sensitive to lysine than that in Oh51 Ao2. Consequently, aspartate kinase 2 is the more promising gene involved in this quantitative locus.
Degree ProgramGraduate College