Molecular studies on `marginal overdominance` in maize

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In the proposed project, the hypothesis of marginal overdominance will be examined by gene expression and enzyme activity studies. Six unrelated interpool hybrids will be compared with their twelve parent lines in one juveline (4-leaf stage) and two adult-plant stages (heading, early grain filling). The study will focus on six already isolated and sequenced (Zea mays data bank) genes encoding important enzymes of the carbohydrate and protein metabolism (sps1, spp1, c-/p-/m-AspAT, gln4). For comparison, the transcription factor Dwarf8 (d8) will be included, for which sequence alignments are available for a large sample of inbred lines, and significant associations between DNA polymorphism and quantitative trait variation were detected (Thornsberry et al. 2001). Gene expression will be analysed by Northern-blotting and enzyme activity according to established protocols. Banding intensity will be measured photometrically or by means of a phosphoimager. PCR primers will be designed to amplify fragments of the absoveygenes from genomic DNA of the parent lines. The amplified fragments will be sequenzed to determine the nucleotide polymorphism for each pair of parent lines. Analogously, the electrophoretic mobility of the enzymes will be assessed. To our knowledge, the proposed project will be the first molecular study examining marginal overdominance as a possible cause of heterosis.