Antifungal activities of metabolites produced by a termite-associated Streptomyces canus BYB02

Two main antifungal metabolites resistomycin and tetracenomycin D were isolated and purified from a termite-associated Streptomyces canus BYB02 by column chromatography. The structures of isolated compounds were determined on the basis of extensive spectroscopic analysis. Resistomycin possessed strong activities against mycelial growth of Valsa mali (IC(50) = 1.1 μg/mL) and Magnaporthe grisea (IC(50) = 3.8 μg/mL), which were comparable to those of referenced cycloheximide, with IC(50) values of 2.3 and 0.3 μg/mL, respectively. A further spore germination test showed that resistomycin exhibited potent reduction in spore germination for M. grisea , with an IC(50) value of 5.55 μg/mL. Finally, the in vivo antifungal activity experiment showed that resistomycin possessed significant preventive efficacy against rice blast, which was more potent than that of referenced carbendazim, with control efficacies of 66.8 and 58.7%, respectively. The present results suggest that resistomycin has potential to be used as a fungicide.

Phytotoxic effects of trichothecenes on the growth and morphology of Arabidopsis thaliana

Non-volatile sesquiterpenoids, a trichothecene family of phytotoxins such as deoxynivalenol (DON) and T-2 toxin, contain numerous molecular species and are synthesized by phytopathogenic Fusarium species. Although trichothecene chemotypes might play a role in the virulence of individual Fusarium strains, the phytotoxic action of individual trichothecenes has not been systematically studied. To perform a comparative analysis of the phytotoxic action of representative trichothecenes, the growth and morphology of Arabidopsis thaliana growing on media containing these compounds was investigated. Both DON and diacetoxyscirpenol (DAS) preferentially inhibited root elongation. DON-treated roots were less organized compared with control roots. Moreover, preferential inhibition of root growth by DON was also observed in wheat plants. In addition, T-2 toxin-treated seedlings exhibited dwarfism with aberrant morphological changes (e.g. petiole shortening, curled dark-green leaves, and reduced cell size). These results imply that the phytotoxic action of trichothecenes differed among their molecular species. Cycloheximide (CHX)-treated seedlings displayed neither feature, although it is known that trichothecenes inhibit translation in eukaryotic ribosomes. Microarray analyses suggested that T-2 toxin caused a defence response, the inactivation of brassinosteroid (BR), and the generation of reactive oxygen species in Arabidopsis. This observation is in agreement with our previous reports in which trichothecenes such as T-2 toxin have an elicitor-like activity when infiltrated into the leaves of Arabidopsis. Since it has been reported that BR plays an important role in a broad range of disease resistance in tobacco and rice, inactivation of BR might affect pathogenicity during the infection of host plants by trichothecene-producing fungi.