Agronomy and Horticulture, Department of


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A DISSERTATION Presented to the faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Agronomy (Plant Breeding and Genetics), Under the Supervision of Professors Tom Clemente and Ismail Dweikat. Lincoln, Nebraska: December, 2010


Sorghum [Sorghum bicolor (L.) Moench] is the fifth most important cereal crop world-wide as well as an important source of feed, fiber and biofuel. It is a C4 plant and is well adapted to environments subject to high temperature and water limitation. Despite these agronomic qualities, it suffers from limitations of sensitivity to low temperature and the grain has drawbacks in relation to functionality and digestibility. The objectives of this study are: 1. To promote seed germination at low temperature and to enhance the seedling cold tolerance. 2. To enhance the grain digestibility and functionality. In an attempt to augment cold tolerance, we introduced the glycine rich RNA binding protein gene atRZ-1a from Arabidopsis, Bcl-2 mRNA sequence 725-1428 representing the 3’ non coding region of the gene from humans and rice Ca-dependent protein kinase 7 (OsCDPK7), all of which are known to improve the cold tolerance of plants. None of these genes resulted in the improvement of cold tolerance in sorghum. On the other hand ectopic expression of OsCDPK7 in sorghum led to local lesions formation in leaves. The data generated from this study indicated that constitutive modulation of the CDPK signal transduction pathway in sorghum can trigger a localized cell death response. Further we targeted improving the grain digestibility and functionality. To accomplish this objective we introduced the wheat high-molecular-weight glutenin subunits (HMW-GS) into sorghum which are known to have significant impact on flour quality. Transgenic events expressing HMW-GS showed improvement in protein digestibility of the uncooked ground grain. In separate complementary set of sorghum transformations we introduced genetic cassettes designed to specifically down-regulate the accumulation of the sorghum alpha and gamma kafirins. Down-regulation of alpha kafirin showed presence of distorted protein bodies in the transgenic seed. The long-term goal of this project is to stack the HMW-GS trait with the modulated kafirins events, as a means to address both end-use functionality and digestibility.