Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/18/2013
Publication Date: 9/1/2013
Citation: Lygin, A., Zernova, O., Hill, C., Kholina, N., Widholm, J., Hartman, G.L., Lozovaya, V. 2013. Glyceollin is an important component of soybean plant defense against Phytophthora sojae and Macrophomina phaseolina. Phytopathology. 103:984-994. Interpretive Summary: Biotic stress is a primary cause of soybean crop loss worldwide. For plants to withstand and survive stresses produced by biotic constraints, different resistance mechanisms have evolved. The ability to recognize invading microbes and then respond biochemically to prevent or limit the invasion in plant cells is a well-established plant process that has been studied extensively. Phenylpropanoids are known to be involved in plant-pathogen interactions and can be strongly toxic or inhibitory to pathogens. The biosynthesis of glyceollin occurs via the isoflavonoid branch of the phenylpropanoid pathway. In this study, we showed that suppression of glyceollin increased susceptibility of soybeans to soybean pathogens. These results provide evidence that rapid glyceollin biosynthesis during infection contributes to the innate soybean defense response. This reasearch is important for plant biotechnologist, biochemists, and others interested in the role of plant defense compounds to pathogen attack.
Technical Abstract: Transgenic soybean plants were generated using bombardment of embryogenic cultures with the PAL5 (phenylalanine ammonia lyase), CHS6 (chalcone synthase) and IFS2 (isoflavone synthase) genes in sense orientation, driven by the cotyledon-preferable lectin promoter, or with the IFS2 (isoflavone synthase) gene in sense orientation driven by the CsVMV constitutive promoter. Transgenic plants, with suppressed synthesis of isoflavones, and non-transgenic plants were compared after being inoculated with two common soybean pathogens, Macrophomina phaseolina and Phytophthora sojae. Down regulation of isoflavone synthesis in the whole soybean plant or only in the seeds caused a strong inhibition of the pathogen-inducible glyceollin, which resulted in increased susceptibility of the transgenic plants to both pathogens. These results provide further evidence that rapid glyceollin biosynthesis during infection contributes to the innate soybean defense response. 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 to the un-transformed control during the 10d observation period, with the precursors of isoflavone synthesis being accumulated in the cotyledons of transgenic plants. These results indicated that the lectin promoter could be active not only during seed development, but also during seed germination.