Regulation of plant immunity through modulation of phytoalexin synthesis.

Soybean hairy roots transformed with the resveratrol synthase and resveratrol oxymethyl transferase genes driven by constitutive Arabidopsis actin and CsVMV promoters were characterized. Transformed hairy roots accumulated glycoside conjugates of the stilbenic compound resveratrol and the related compound pterostilbene, which are normally not synthesized by soybean plants. Expression of the non-native stilbenic phytoalexin synthesis in soybean hairy roots increased their resistance to the soybean pathogen Rhizoctonia solani.

Inhibitory effects of stilbenes on the growth of three soybean pathogens in culture.

The effects of resveratrol and pterostilbene on in vitro growth of three soybean pathogens were tested to determine whether these stilbenic compounds could potentially be targets to increase innate resistance in transgenic soybean plants. Growth of Macrophomina phaseolina, Rhizoctonia solani, and Sclerotinia sclerotiorum was measured on solid and in liquid media amended with resveratrol and pterostilbene (concentration in the media of resveratrol at 100 μg/ml and pterostilbene at 25 μg/ml). All three fungi were very sensitive to pterostilbene in potato dextrose agar (PDA), which reduced colony area of each of the three pathogens to less than half of the control 3 days after incubation.

Glyceollin is an important component of soybean plant defense against Phytophthora sojae and Macrophomina phaseolina.

The response of soybean transgenic plants, with suppressed synthesis of isoflavones, and nontransgenic plants to two common soybean pathogens, Macrophomina phaseolina and Phytophthora sojae, was studied. Transgenic soybean plants of one line used in this study were previously generated via bombardment of embryogenic cultures with the phenylalanine ammonia lyase, chalcone synthase, and isoflavone synthase (IFS2) genes in sense orientation driven by the cotyledon-preferable lectin promoter (to turn genes on in cotyledons), while plants of another line were newly produced using the IFS2 gene in sense orientation driven by the Cassava vein mosaic virus constitutive promoter (to turn genes on in all plant parts). Nearly complete inhibition of isoflavone synthesis was found in the cotyledons of young seedlings of transgenic plants transformed with the IFS2 transgene driven by the cotyledon-preferable lectin promoter compared with the untransformed control during the 10-day observation period, with the precursors of isoflavone synthesis being accumulated in the cotyledons of transgenic plants.

Response of soybean pathogens to glyceollin.

Plants recognize invading pathogens and respond biochemically to prevent invasion or inhibit colonization in plant cells. Enhancing this response in crop plants could improve sustainable methods to manage plant diseases. To enhance disease resistance in soybean, the soybean phytoalexin glyceollin was assessed in soybean hairy roots of two soybean genotypes, Spencer and PI 567374, transformed with either soybean isoflavone synthase (IFS2) or chalcone synthase (CHS6) genes that were inoculated with the soybean pathogens Diaporthe phaseolorum var.

Modification of isoflavones in soybean seeds via expression of multiple phenolic biosynthetic genes.

To modify the level and composition of isoflavones, the important bioactive constituents of soybean seeds, soybean was transformed via co-bombardment of embryogenic cultures with three DNA cassettes containing the CHS6-chalcone synthase and IFS2-isoflavone synthase genes, and a fragment of PAL5-phenylalanine ammonia-lyase gene, all in sense orientation under the lectin promoter mixed with the selectable marker gene, HPT (hygromycin phosphotransferase) under the 35S promoter. Four of six fertile lines produced integrated all four genes. Isoflavone levels were lower in T1 mature seeds of 5 of the 6 lines compared to the control.

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.

Isoflavonoid accumulation in soybean hairy roots upon treatment with Fusarium solani.

Hairy roots were initiated from two soybean [Glycine max (L.) Merr.] genotypes with different susceptibility (susceptible 'Spencer' and partially resistant 'PI567.