Modification of phenolic metabolism in soybean hairy roots through down regulation of chalcone synthase or isoflavone synthase
Soybean hairy roots, transformed with the soybean chalcone synthase (CHS6) or isoflavone synthase (IFS2) genes, with dramatically decreased capacity to synthesize isoflavones were produced to determine what effects these changes would have on susceptibility to a fungal pathogen. The isoflavone and coumestrol concentrations were decreased by about 90% in most lines apparently due to gene silencing. The IFS2 transformed lines had very low IFS enzyme activity in microsomal fractions as measured by the conversion of naringenin to genistein. The CHS6 lines with decreased isoflavone concentrations had 5 to 20-fold lower CHS enzyme activities than the appropriate controls. Both IFS2 and CHS transformed lines accumulated higher concentrations of both soluble and cell wall bound phenolic acids compared to controls with higher levels found in the CHS6 lines indicating alterations in the lignin biosynthetic branch of the pathway. Induction of the soybean phytoalexin glyceollin, of which the precursor is the isoflavone daidzein, by the fungal pathogen Fusarium solani f. sp. glycines (FSG) that causes soybean sudden death syndrome (SDS) showed that the low isoflavone transformed lines did not accumulate glyceollin while the control lines did. The (iso)liquritigenin content increased upon FSG induction in the IFS2 transformed roots indicating that the pathway reactions before this point can control isoflavonoid synthesis. The lowest fungal growth rate on hairy roots was found on the FSG partially resistant control roots followed by the SDS sensitive control roots and the low isoflavone transformants. The results indicate the importance of phytoalexin synthesis in root resistance to the pathogen.
KeywordsDisease Genetic engineering Phenylpropanoids Resistance Hairy roots Soybean
This study was supported in part by funds from the Illinois Soybean Program Operating Board, the United Soybean Board, the North Central Soybean Research Program, the Soybean Disease Biotechnology Center, the Illinois Agricultural Experiment Station, and the USDA Agricultural Research Service.
- Bhattacharyya MK, Ward EWB (1985) Differential sensitivity of Phytophthora megasperma f sp. glycinea to glyceollin isomers. Physiol Mol Plant Pathol 27:299–310Google Scholar
- Dellaporta S (1994) Plant DNA miniprep and microprep. In: Freeling M, Walbot V (eds) The Maize Handbook. Springer, Berlin Heidelberg New York, pp 522–525Google Scholar
- Edwards R, Kessmann H (1992) Isoflavonoid phytoalexin and their biosynthetic enzymes. In SJ Gurr, MJ McPherson, DJ Bowles (ed) Molecular plant pathology: a practical approach, vol 2. IRL Press, Oxford, pp 45–62Google Scholar
- Graham TL, Graham MY (1991) Glyceollin elicitors induce major but distinctly different shifts in isoflavonoid metabolism in proximal and distal soybean cell populations. Mol Plant–Microbe Interact 4:60–68Google Scholar
- Harborne JB (1964) Ultraviolet spectroscopy of flavonoids. In: Pridham JB (ed) Methods in polyphenol chemistry. Proceedings of the plant phenolics group symposium, Oxford, April 1963, Pergamon Press, pp 13–37Google Scholar
- Lozovaya VV, Lygin AV, Li S, Hartman GL, Widholm JM (2004a) Biochemical response of soybean roots to Fusarium solani f. sp. glycines infection. Crop Sci 44:819–826Google Scholar
- McLafferty FW, Turecek F (1993) Interpretation of mass spectra. IV (ed) University science books, Mill Valley, CaliforniaGoogle Scholar
- Paxton JD (1974) Phytoalexins, phenolics and other antibiotics in roots resistant to soil-borne fungi. In: Bruehl GW (ed) Biology and control of soil-borne plant pathogens. St Paul, pp 185–192Google Scholar
- Paxton JD, Groth J (1994) Constraints on pathogens attacking plants. Critical Rev Plant Sci 13:77–95Google Scholar
- Savka MA, Ravillion B, Noel GR, Farrand SK (1990) Induction of hairy roots on cultivated soybean genotypes and their use to propagate the soybean cyst nematode. Phytopathol 80:503–508Google Scholar
- Widholm J (2004) Progress in transforming the recalcitrant soybean. Chapter 11 In: Liang GH, Skinner DZ (ed) Genetically modified crops: their development, uses, and risks. The Haworth Press Inc, New York, pp 259–280Google Scholar