Modification Phenolic Metabolism in Soybean Hairy Roots Through Down Regulation of Chalcone Synthase or Isoflavone Synthase

Authors: LOZOVAYA, VERA - UNIVERSITY OF ILLINOIS; LYGIN, ANATOLIY - UNIVERISTY OF ILLINOIS; ZERNOVA, OLGA - UNIVERSITY OF ILLINOIS; Li, Shuxian; Hartman, Glen; WIDHOLM, JACK - UNIVERISTY OF ILLINIOS

Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2006
Publication Date: 1/10/2007
Citation: Lozovaya, V.V., Lygin, A.A., Zernova, O.V., Li, S., Hartman, G.L., Widholm, J.M. 2007. Modification Phenolic Metabolism in Soybean Hairy Roots Through Down Regulation of Chalcone Synthase or Isoflavone Synthase. Planta 225:665-679. (Online DOI: 10.1007/s00425-006-0368-z)

Interpretive Summary: The production of phytoalexins, low molecular weight antimicrobial compounds, is considered to be a very important mechanism that can be triggered in plant cells upon invasion by various pathogenic microbes. Hairy roots (cultured in Petri dishes) of two soybean cvs. PI567.374 and Spencer were used to study the biochemical response to infection by the fungal pathogen Fusarium solani f. sp. glycines (FSG) that causes sudden death syndrome (SDS). Low isoflavone transformed lines did not accumulate glyceollin, a phytoalexin, while the control lines did. The cv. with partial resistance had higher glyceollin than the sensitive cv. When the growth of FSG was measured on the hairy roots, the lowest growth rate was found on the FSG partially resistant control roots followed by the SDS sensitive control roots and the low isoflavone transformants. These results demonstrate that the isoflavonoid pathway can be manipulated and that FSG growth on soybean hairy roots is inversely proportional to the glyceollin content, which indicates the importance of phytoalexin synthesis in root resistance to the pathogen. This basic information is important to scientists interested in the biochemical aspects of how plants defend themselves against pathogen invasion.

Technical Abstract: Hairy roots of two soybean cvs. PI567.374 and Spencer, expressing the soybean chalcone synthase (CHS6) or isoflavone synthase (IFS) gene with dramatically decreased capacity to synthesize isoflavones were produced via Agrobacterium rhizogenes transformation to determine what effect 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 IFS low isoflavones lines were yellow due to the accumulation of the daidzein precursor isoliquritigenin. These lines also 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 the IFS and CHS6 transformed lines accumulated both soluble and cell wall bound phenolic acids with higher levels found in the CHS6 lines. Induction of the soybean phytoalexin glyceollin, whose precursor is the isoflavone daidzein, by the fungal pathogen Fusarium solani f. sp. glycines (FSG) that causes sudden death syndrome (SDS) showed that the low isoflavone transformed lines did not accumulate glyceollin while the control lines did. The cv. with partial resistance had higher glyceollin than the sensitive cv. The (iso)liquritigenin content increased upon FSG induction indicating that the pathway reactions above this point can control isoflavonoid synthesis. When the growth of FSG was measured on the hairy roots, the lowest growth rate was found on the FSG partially resistant control roots followed by the SDS sensitive control roots and the low isoflavone transformants. These results demonstrate that the isoflavonoid pathway can be manipulated and that FSG growth on soybean hairy roots is inversely proportional to the glyceollin content, which indicates the importance of phytoalexin synthesis in root resistance to the pathogen.