Modification of phenolic metabolism in soybean hairy roots through down regulation of chalcone synthase or isoflavone synthase

Abstract

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.

RNAi Silencing of Genes for Elicitation or Biosynthesis of 5-Deoxyisoflavonoids Suppresses Race-Specific Resistance and Hypersensitive Cell Death in Phytophthora sojae Infected Tissues

“…Accompanying this was the accumulation of relatively small amounts of liquiritigenin, the immediate precursor of daidzein. Recently, it was reported that cosuppression of IFS in soybean hairy roots led to the accumulation of p-hydroxybenzoic acid and vanillic acid in the soluble fraction (Lozovaya et al, 2007). However, these metabolites did not appear as major peaks in metabolic profiles of our IFS RNAi-silenced tissues.…”

Spatio Temporal Influence of Isoflavonoids on Bacterial Diversity in the Soybean Rhizosphere

“…Additionally, compared with sugars, amino acids, and organic acids present in rhizodeposits, isoflavonoids (and other secondary metabolites) are species-specific and are more likely to recruit unique microbial communities. Silencing of isoflavonoid biosynthesis in the roots did not significantly influence other metabolites in the phenylpropanoid pathway, except the accumulation of liquiritigenin (the substrate of IFS), p-hydroxy benzoic acid, coumaric acid, and p-hydroxybenzaldehyde (Lozovaya et al 2007;Subramanian et al 2006) (data not shown). We cannot exclude the possibility that a small proportion of the changes in root bacterial profiles could be due to these relatively small changes in nontarget phenylpropanoids.…”

Soy, phytoestrogens and their impact on reproductive health

“…Isoflavones play important roles as signal molecules for inhibiting pathogen attacks (Lozovaya et al, 2007;Zabala et al, 2006) and for plant-microbe symbiotic interactions (Subramanian et al, 2006;Sugiyama et al, 2007). Genistin and daidzin is initiated by the conversion of the essential amino acid L-phenylalanine into p-Coumaroyl-CoA.…”