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.

Phytopathogenic fungi such as Fusarium spp. synthesize trichothecene family phytotoxins. Although the type B trichothecene, deoxynivalenol (DON), is thought to be a virulence factor allowing infection of plants by their trichothecene-producing Fusarium spp., little is known about effects of trichothecenes on the defense response in host plants. Therefore, in this article, we investigated these effects of various trichothecenes in Fusarium-susceptible Arabidopsis thaliana. Necrotic lesions were observed in Arabidopsis leaves infiltrated by 1 μM type A trichothecenes such as T-2 toxin. Trichothecene-induced lesions exhibited dead cells, callose deposition, generation of hydrogen peroxide, and accumulation of salicylic acids. Moreover, infiltration by trichothecenes caused rapid and prolonged activation of two mitogen-activated protein kinases and induced expression of both PR-1 and PDF1.2 genes. Thus, type A trichothecenes trigger the cell death by activation of an elicitor-like signaling pathway in Arabidopsis. Although DON did not have such an activity even at 10 μM, translational inhibition by DON was observed at concentrations above 5 μM. These results suggested that DON is capable of inhibiting translation in Arabidopsis cells without induction of the elicitor-like signaling pathway.

AtNFXL1, an Arabidopsis homologue of the human transcription factor NF-X1, functions as a negative regulator of the trichothecene phytotoxininduced defense response. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Journal: The Plant JournalTrichothecenes are a closely related family of phytotoxins produced by phytopathogenic fungi. In Arabidopsis, expression of AtNFXL1, a homologue of the putative human transcription repressor NF-X1, was significantly induced by application of type A trichothecenes, such as T-2 toxin. An atnfxl1 mutant growing on medium lacking trichothecenes showed no phenotype, whereas a hypersensitivity phenotype was observed in T-2 toxin-treated atnfxl1 mutant plants. Microarray analysis indicated that several defense-related genes (i.e. WRKYs, EDS5, ICS1, etc.) were upregulated in T-2 toxin-treated atnfxl1 mutant compared to wild type plants. In addition, enhanced salicylic acid (SA) accumulation was observed in T-2 toxin-treated atnfxl1 mutant plants, which suggests that AtNFXL1 functions as a negative regulator of these defense-related genes via an SA-dependent signaling pathway. We also found that expression of AtNFXL1 was induced by SA and flg22 treatment. Moreover, the atnfxl1 mutant was less susceptible to a compatible phytopathogen, Pseudomonas syringae pv. tomato strain DC3000 (Pst DC3000). Taken together, these results indicate 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60Trichothecenes are a major type of mycotoxin, and are important in human health due to the risk of ingesting contaminated food (Kimura et al., 2006). Phytopathogenic fungi capable of producing trichothecenes are found throughout the world, and include certain species of Fusarium, Myrotherium and Stachybotrys (Eudes et al., 2001). The production of mycotoxins by these species of phytopathogenic fungi is determined by genetic factors and environmental growth conditions. Trichothecenes have a sesquiterpenoid ring structure, and can be classified according to the presence or absence of characteristic functional groups (Shifrin and Anderson, 1999). Type A trichothecenes, such as T-2 toxin, and type B trichothecenes, such as deoxynivalenol (DON), are natural contaminants of certain agricultural commodities, as well ...

Beta-mannanase from Penicillium oxalicum SO efficiently hydrolyzed guar galactomannan to galacto-manno-oligosaccharides. Gel filtration estimated the molecular weight of the beta-mannanase as 35 000 and SDS-PAGE as 29 000. The optimum pH was around 5 while a stable pH was reached in the range of 3-6. Optimum temperature was around 60 degrees C at pH 5, while under 60 degrees C activity was stable. HPLC analysis detected oligosaccharides with degrees of polymerization (DP) of 2 to 7 and 2 to 6 released on hydrolysis of guar and locust bean gums, respectively; about 92% of the released sugars were oligosaccharides. In analysis of the sugar distribution on MALDI-TOF-MS, major products of DP 6 and 7 and DP 5 and 6 were confirmed in hydrolysates of guar gum and locust bean gum, respectively. One of the main oligosaccharides released from guar gum, with DP 7, had a high galactose content (Gal/Man = 0.76) and corresponded to a blockwise galactose-substituted mannan type in galactomannan.