Bioorganic chemistry of host-specific toxins from microbes and self-defense substances from plants involved in host-parasite interactions

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Objective : In interactions between a host-plant and pathogen, a host-plant produces self-defense substances against microbes and a pathogen sometimes produces a host-selective substances. Objectives in our experiments were : a) Clarification of structure-activity relationships of HMT- and PM-toxins. Isolation of phytotoxins from Pyricularia oryzae and Helminthosporium sorghicola. b) Studies on resistant mechanism of rice plant against a bacterial leaf blight caused by Xanthomonas campestris pv. oryzae. c) Isolation of antifungal substances from leaves of wild rice, Oryza officinalis, W0002 which shows resistant against rice blast disease. Isolation and identification of antifungal substances from other plant extracts.Results : a) i) Above 30 compounds related to HMT- and PM-toxins were synthesized and compared their activity using a susceptible corn leaf. At least four beta-ketol groups are required to express high activity and also spacing methylene functions between each beta-ketol group required above seven for high activity. ii) Two novel pyriculol related compounds were isolated and identified as phytotoxins from the solid culture of Pyricularia oryzae. b) Ten novel antibacterial diterpenes were isolated from a flag leaf of abacterial leaf blight-resistant cultivar of rice plant and determined their structures. Quantitative analysis of oryzalides using GC-MS-SIM suggested that a role of oryzalides might be an inhibitin. c) (-)-jasmonic acid and two novel fatty acids, 12-hydroxy-9(Z)-dodecenoic acid and 11-hydroxy-9(Z)-undecenoic acid, were isolated and identified from healthy leaves of wild rice, Oryza officinalis W0002 as a antifungal substance.