|Guill, Katherine - Kate|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2002
Publication Date: 9/1/2002
Citation: SZALMA, S.J., SNOOK, M.E., BUSHMAN, B.S., HOUCHINS, K.E., MCMULLEN, M.D. DUPLICATE LOCI AS QTL: THE ROLE OF CHALCONE SYNTHASE LOCI IN FLAVONE AND PHENYLPROPANOID BIOSYNTHESIS IN MAIZE. CROP SCIENCE. 2002. v. 42. p. 1679-1687. Interpretive Summary: Understanding the relationships between genetic effects and the regulation of genes in biochemical pathways is important if we are to make predictive manipulation of biochemical pathways for crop improvement. In this study, we determined the relative roles of duplicate loci, e.g., two genes that do similar functions, on the chemical output of two pathways. Each of these pathways produce chemicals with the potential to provide resistance to the corn earworm, a major pest of corn in the United States. We demonstrated that each of the two genes can work independently and together to affect the amount of chemicals synthesized. In addition, we demonstrated that the flow of chemical intermediates between pathways is seen as a major genetic effect. These results are significant to scientists because they demonstrate that manipulation of one pathway can be use to modify the output of a second pathway allowing designer corn varieties expressing different amounts of two different anti-insect chemicals.
Technical Abstract: The C-glycosyl flavone maysin is an important component of corn earworm (Helicoverpa zea Boddie) (CEW) resistance in maize (Zea mays L.) silks. Chlorogenic acid (CGA), a product of the phenylpropanoid pathway, has also been implicated in CEW antibiosis. The transition from the 9-carbon phenylpropanoid to the 15-carbon flavonoid pathway represents a potentially yimportant regulation point in C-glycosyl flavone biosynthesis. The enzyme chalcone synthase (CHS) catalyzes this reaction and is represented by a set of duplicate loci in maize, colorless2 (c2) and white pollen1 (whp1). Chromosomal regions of the maize genome have been identified as quantitative trait loci (QTL) for maysin synthesis that correspond to these two loci. Our objective was to investigate the role of CHS in flavone and CGA biosynthesis. We tested c2 and whp1 as candidate loci using three related F2 populations segregating for both structural and regulatory loci. .Results from statistical and QTL analyses: i) Support earlier findings of the requirement of a functional pericarp color1 (p1) allele for C-glycosyl flavone biosynthesis. ii) Demonstrate that variation at the c2 region on chromosome 4 influences both maysin and CGA levels in silks. iii) Reveal a dosage-dependent relationship between c2 and whp1 in which the whp1 region acts cooperatively with functional c2 to increase flavones and partially compensates for nonfunctional c2. iv) Demonstrate that mutations in c2 and whp1 shunt intermediates from maysin synthesis to CGA. These results demonstrate that CHS function is a regulatory focal point of substrate flow between the flavone and phenylpropanoid pathways.