Planta (2007) 225:665–679 DOI 10.1007/s00425-006-0368-z 123 ORIGINAL ARTICLE ModiWcation of phenolic metabolism in soybean hairy roots through down regulation of chalcone synthase or isoXavone synthase Vera V. Lozovaya · Anatoliy V. Lygin · Olga V. Zernova · Alexander V. Ulanov · Shuxian Li · Glen L. Hartman · Jack M. Widholm Received: 11 May 2006 / Accepted: 27 July 2006 / Published online: 22 August 2006  Springer-Verlag 2006 Abstract Soybean hairy roots, transformed with the soybean chalcone synthase (CHS6) or isoXavone syn- thase (IFS2) genes, with dramatically decreased capacity to synthesize isoXavones were produced to determine what eVects these changes would have on susceptibility to a fungal pathogen. The isoXavone and coumestrol concentrations were decreased by about 90% in most lines apparently due to gene silencing. The IFS2 trans- formed lines had very low IFS enzyme activity in microsomal fractions as measured by the conversion of naringenin to genistein. The CHS6 lines with decreased isoXavone concentrations had 5 to 20-fold lower CHS enzyme activities than the appropriate con- trols. Both IFS2 and CHS transformed lines accumu- lated higher concentrations of both soluble and cell wall bound phenolic acids compared to controls with higher levels found in the CHS6 lines indicating altera- tions in the lignin biosynthetic branch of the pathway. Induction of the soybean phytoalexin glyceollin, of which the precursor is the isoXavone daidzein, by the fungal pathogen Fusarium solani f. sp. glycines (FSG) that causes soybean sudden death syndrome (SDS) showed that the low isoXavone 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 isoXavonoid 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 isoXavone transformants. The results indicate the importance of phytoalexin synthesis in root resistance to the pathogen. Keywords Disease · Genetic engineering · Phenylpropanoids · Resistance · Hairy roots · Soybean Introduction The production of phytoalexins, low molecular weight antimicrobial compounds, is considered to be a very important mechanism that can be triggered in plant Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable. V. V. Lozovaya (&) · A. V. Lygin · O. V. Zernova · A. V. Ulanov · J. M. Widholm Department of Crop Sciences, University of Illinois, 1201 W. Gregory Dr., Urbana, IL 61801, USA e-mail: lozovaya@uiuc.edu A. V. Lygin e-mail: lygin@uiuc.edu O. V. Zernova e-mail: zernova@uiuc.edu A. V. Ulanov e-mail: ulanov@uiuc.edu J. M. Widholm e-mail: widholm@uiuc.edu G. L. Hartman USDA, Agricultural Research Service, University of Illinois, 1101 W. Peabody Dr., Urbana, IL 61801, USA e-mail: ghartman@uiuc.edu S. Li USDA/ARS, MSA, CGPRU, 141 Experiment Station Road, P.O. Box 345, Stoneville, MS 38776, USA e-mail: SLI@msa-stoneville.ars.usda.gov