Robustness of QTLs across germplasm pools using a model quantitative trait

Knowledge of the inheritance of C-glycosyl flavone synthesis in maize ( Zea mays L.) silk tissues has been acquired through detailed genetic studies involving primarily germplasm from the Corn Belt Dent race. To test the robustness of this genetic knowledge, we examined C-glycosyl flavone synthesis in a genetically distinct germplasm pool, popcorn. C-glycosyl flavone profiles and levels and the involvement of three specific genes/quantitative trait loci (p, pr1, and sm1) in C-glycosyl flavone synthesis were examined in popcorn germplasm representing at least two races and various diverse geographic regions. Twenty-four inbred lines and 23 hybrids involving these inbred lines and inbred line R17 were characterized for their flavone profiles and levels in silk tissues. Two F2 mapping populations were constructed to examine the involvement of p, pr1, and sm1 on C-glycosyl flavone synthesis. C-glycosyl flavone levels threefold higher than previously reported in Corn Dent Belt materials and a novel class of compounds were discovered. The gene action of sm1 was different, the functional p allele was not always dominant, and pr1 did not affect maysin synthesis. Based on this rather simplistic “model” quantitative trait, it appears that caution should be exercised when attempting to apply quantitative trait locus knowledge accumulated in one germplasm base to a germplasm base that is known to be distinctly unique.

Induction and Characterization of a NADPH-Dependent Flavone Synthase from Cell Cultures of Soybean

Microsomal preparations from osmotically stressed soybean cells catalyze the conversion of (2S)-naringenin to apigenin in presence of NADPH. In contrast, such preparations from normal soybean cells or from elicitor-challenged cells catalyze the conversion of (2S)-naringenin to genistein (isoflavone synthase). It is concluded that osmotic stress of the cells causes a switch from isoflavone to flavone synthesis. The flavone synthase from osmotically stressed cells corresponds in its properties to the microsomal flavone synthase found in several flowers (G. Stotz and G. Forkmann, Z. Naturforsch. 36c, 737-741 (1981)) and differs from the flavone synthase I from parsley cell cultures which is a soluble Fe2+ and 2-oxoglutarate dependent dioxygenase. Flavone synthase II from soybean has an absolute requirement for NADPH and oxygen. It is inhibited by carbon monoxide in presence of oxygen and this inhibition is reversed by light. It is also inhibited by cytochrome c and by a number of cytochrome P-450 inhibitors. This and other properties show that flavone synthase II is a cytochrome P-450 dependent monooxygenase.