الفهرس 
Introduction
Sorghum phytoalexinsOnly 14 pages are availabe for public view
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Abstract
The thesis focused on answering a challenging question as “why do the metabolic pathways in genetically related species such as sorghum and maize, whose genomes have high degree of synteny and similar suit of regulatory and structural genes, respond differentially to certain biotic stress exerted by pathogenic and nonpathogenic fungi?” My initial research and other’s indicated that sorghum respond to fungal attack by production of flavonoid antimicrobial compounds (phytoalexins) belonging to 3- deoxyanthocyanidins class while maize is defective in this trait. Therefore, we used sorghum as a model system to 1) identify the biochemical and molecular mechanisms that control the synthesis of sorghum phytoalexins, 2) uncover the signaling cascade leading to or co-induced with sorghum phytoalexin biosyhtsis, and 3) attempt to engineer these defense compounds in maize via molecular biology and tissue culture technologies. My research led to the characterization of a transcription factor, called yellow seed1(y1), which controls the biosynthesis of sorghum 3-deoxyanthocyanidins phytoalexins. Sequence comparison of y1 and its maize orthology, pericarp color1 (p1) revealed high degree of similarity in their coding sequences but very poor homology in the regulatory regions. In addition, the two genes have almost the same pattern of expression except that y1 has a significant activity in leaves and is induced by fungal infection. Using the gene gun and tissue culture technologies, we transferred sorghum y1 into maize and produced transgenic maize lines that successfully express the sorghum y1.Our biochemical and molecular analysis of the transgenic maize line indicated that y1 enriched maize with novel flavonoid and phenolic compounds. These compounds enhanced maize resistance against fungal disease like southern leaf blight. We also reported the early induction of Jasmonic acid (JA) but not Salicylic acid (SA) during the biosynthesis of sorghum phytoalexins.