Wednesday, November 15, 2006

Genetic Analysis of isoflavone accumulation during soybean seed development under drought stress.

Juan Gutierrez1, David Sleper1, Henry Nguyen1, Babu Valliyodan1, and Oliver Yu2. (1) University of Missouri, Division of Plant Sciences, Columbia, MO 65211, (2) Donald Danforth Plant Science Center, St. Louis, MO 63132

 Isoflavonoids are important secondary plant metabolites that accumulate mainly in seeds and leaves, although they can also be found in roots, stems, seed coat, embryos, and pods. These compounds are synthesized predominantly in legumes from a branch of the phenylpropanoid pathway, which in addition leads to other important groups of secondary compounds: tannins, flavones, flavonols and anthocyanins. Genistein and daidzein are the major isoflavones in soybean and glycitein is present only in small amounts. Dietary intake of isoflavonoids has been largely related to human health benefits. Among the characteristics attributed to them are estrogenic activity, anti-carcinogenic effect, antioxidant properties, inhibition of reactive nitrogen species, and osteoporosis and heart diseases prevention. In a preliminary study, we analyzed the isoflavone levels of several soybean lines using HPLC. Plant introductions (PI) 437654 and PI 438489B show higher levels, and cv Magellan show lower level of isoflavone. A greenhouse experiment was conducted to study the transcriptional regulation of isoflavone accumulation during drought stress. Soybean plants were water-stressed in the greenhouse in two growth stages, R5 and R7, and the samples were collected at different time points. Gene expression profiling will help identify and discover differentially expressed genes along the phenylpropanoid pathway under drought conditions. Interactions among enzymes, metabolites, and regulatory molecules will provide us a better understanding of the isoflavonoid synthesis and accumulation. At the molecular level, promoter binding of regulatory molecules will be studied. Another major objective of the study is to identify QTLs involved in isoflavone accumulation in 200 F7 RILs developed from the cross Essex x PI 437654. For that, we are placing around 350 SSR markers onto the genetic map. Finally, metabolites involved in isoflavone synthesis will be put on the QTL map through candidate gene approach and the adding of SNP markers to narrow down the QTL area.