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Lutein, a Natural Carotenoid, Induces ?-1,3-Glucan Accumulation on the Cell Wall Surface of Fungal Plant Pathogens.

ABSTRACT: ?-1,3-Glucan, a component of the fungal cell wall, is a refractory polysaccharide for most plants. Previously, we showed that various fungal plant pathogens masked their cell wall surfaces with ?-1,3-glucan to evade plant immunity. This surface accumulation of ?-1,3-glucan was infection specific, suggesting that plant factors might induce its production in fungi. Through immunofluorescence observations of fungal cell walls, we found that carrot (Daucus carota) extract induced the accumulation of ?-1,3-glucan on germlings in Colletotrichum fioriniae, a polyphagous fungal pathogen that causes anthracnose disease in various dicot plants. Bioassay-guided fractionation of carrot leaf extract successfully identified two active substances that caused ?-1,3-glucan accumulation in this fungus: lutein, a carotenoid widely distributed in plants, and stigmasterol, a plant-specific membrane component. Lutein, which had a greater effect on C. fioriniae, also induced ?-1,3-glucan accumulation in other Colletotrichum species and in the phylogenetically distant rice pathogen Cochliobolus miyabeanus, but not in the rice pathogen Magnaporthe oryzae belonging to the same phylogenetic subclass as Colletotrichum. Our results suggested that fungal plant pathogens reorganize their cell wall components in response to specific plant-derived compounds, which these pathogens may encounter during infection.

SUBMITTER: Otaka J

PROVIDER: S-EPMC6273161 | biostudies-literature | 2016 Jul

REPOSITORIES: biostudies-literature

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Lutein, a Natural Carotenoid, Induces α-1,3-Glucan Accumulation on the Cell Wall Surface of Fungal Plant Pathogens.

Otaka Junnosuke J Seo Shigemi S Nishimura Marie M

Molecules (Basel, Switzerland) 20160728 8

α-1,3-Glucan, a component of the fungal cell wall, is a refractory polysaccharide for most plants. Previously, we showed that various fungal plant pathogens masked their cell wall surfaces with α-1,3-glucan to evade plant immunity. This surface accumulation of α-1,3-glucan was infection specific, suggesting that plant factors might induce its production in fungi. Through immunofluorescence observations of fungal cell walls, we found that carrot (Daucus carota) extract induced the accumulation of ...[more]

PMID: 27483218

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Project description:Plants evoke innate immunity against microbial challenges upon recognition of pathogen-associated molecular patterns (PAMPs), such as fungal cell wall chitin. Nevertheless, pathogens may circumvent the host PAMP-triggered immunity. We previously reported that the ascomycete Magnaporthe oryzae, a famine-causing rice pathogen, masks cell wall surfaces with α-1,3-glucan during invasion. Here, we show that the surface α-1,3-glucan is indispensable for the successful infection of the fungus by interfering with the plant's defense mechanisms. The α-1,3-glucan synthase gene MgAGS1 was not essential for infectious structure development but was required for infection in M. oryzae. Lack or degradation of surface α-1,3-glucan increased fungal susceptibility towards chitinase, suggesting the protective role of α-1,3-glucan against plants' antifungal enzymes during infection. Furthermore, rice plants secreting bacterial α-1,3-glucanase (AGL-rice) showed strong resistance not only to M. oryzae but also to the phylogenetically distant ascomycete Cochlioborus miyabeanus and the polyphagous basidiomycete Rhizoctonia solani; the histocytochemical analysis of the latter two revealed that α-1,3-glucan also concealed cell wall chitin in an infection-specific manner. Treatment with α-1,3-glucanase in vitro caused fragmentation of infectious hyphae in R. solani but not in M. oryzae or C. miyabeanus, indicating that α-1,3-glucan is also involved in maintaining infectious structures in some fungi. Importantly, rapid defense responses were evoked (a few hours after inoculation) in the AGL-rice inoculated with M. oryzae, C. miyabeanus and R. solani as well as in non-transgenic rice inoculated with the ags1 mutant. Taken together, our results suggest that α-1,3-glucan protected the fungal cell wall from degradative enzymes secreted by plants even from the pre-penetration stage and interfered with the release of PAMPs to delay innate immune defense responses. Because α-1,3-glucan is nondegradable in plants, it is reasonable that many fungal plant pathogens utilize α-1,3-glucan in the innate immune evasion mechanism and some in maintaining the structures.

Project description:β-(1,3)-Glucan, the major fungal cell wall component, ramifies through β-(1,6)-glycosidic linkages, which facilitates its binding with other cell wall components contributing to proper cell wall assembly. Using Saccharomyces cerevisiae as a model, we developed a protocol to quantify β-(1,6)-branching on β-(1,3)-glucan. Permeabilized S. cerevisiae and radiolabeled substrate UDP-(14C)glucose allowed us to determine branching kinetics. A screening aimed at identifying deletion mutants with reduced branching among them revealed only two, the bgl2Δ and gas1Δ mutants, showing 15% and 70% reductions in the branching, respectively, compared to the wild-type strain. Interestingly, a recombinant Gas1p introduced β-(1,6)-branching on the β-(1,3)-oligomers following its β-(1,3)-elongase activity. Sequential elongation and branching activity of Gas1p occurred on linear β-(1,3)-oligomers as well as Bgl2p-catalyzed products [short β-(1,3)-oligomers linked by a linear β-(1,6)-linkage]. The double S. cerevisiae gas1Δ bgl2Δ mutant showed a drastically sick phenotype. An ScGas1p ortholog, Gel4p from Aspergillus fumigatus, also showed dual β-(1,3)-glucan elongating and branching activity. Both ScGas1p and A. fumigatus Gel4p sequences are endowed with a carbohydrate binding module (CBM), CBM43, which was required for the dual β-(1,3)-glucan elongating and branching activity. Our report unravels the β-(1,3)-glucan branching mechanism, a phenomenon occurring during construction of the cell wall which is essential for fungal life.IMPORTANCE The fungal cell wall is essential for growth, morphogenesis, protection, and survival. In spite of being essential, cell wall biogenesis, especially the core β-(1,3)-glucan ramification, is poorly understood; the ramified β-(1,3)-glucan interconnects other cell wall components. Once linear β-(1,3)-glucan is synthesized by plasma membrane-bound glucan synthase, the subsequent event is its branching event in the cell wall space. Using Saccharomyces cerevisiae as a model, we identified GH72 and GH17 family glycosyltransferases, Gas1p and Bgl2p, respectively, involved in the β-(1,3)-glucan branching. The sick phenotype of the double Scgas1Δ bgl2Δ mutant suggested that β-(1,3)-glucan branching is essential. In addition to ScGas1p, GH72 family ScGas2p and Aspergillus fumigatus Gel4p, having CBM43 in their sequences, showed dual β-(1,3)-glucan elongating and branching activity. Our report identifies the fungal cell wall β-(1,3)-glucan branching mechanism. The essentiality of β-(1,3)-glucan branching suggests that enzymes involved in the glucan branching could be exploited as antifungal targets.

Project description:Acanthamoeba castellanii (Ac) and macrophages share structural, morphological, physiological and biochemical similarities, including the ability to phagocyte a myriad of microorganisms in the environments they live. Whereas there is voluminous information on phagocytic receptors of macrophages, for Ac, the understanding of how the recognition of extracellular microorganisms works still awaits elucidation. Recently, our group described mannose-binding proteins expressed on the surface of the trophozoites. However, as soluble mannose did not inhibit entirely the process, other interactions might be possible. In the present work, we aimed to characterize the potential Ac proteins able to recognize the polysaccharide β-1,3-glucan on fungal surfaces. Our data demonstrate that Ac could bind curdlan or laminarin on its surface as detected by Dectin-1-Fc and fluorescent conjugate, suggesting the presence of β-1,3-glucan binding molecules. Optical tweezers detected higher adhesion affinity of laminarin or curdlan coated beads to A. castellanii (characteristic time of 46.9 s and 43.9 s, respectively) in comparison control beads (BSA or dextran-coated). In agreement, a H. capsulatum (Hc) G217B having β-1,3-glucan as the most external layer strongly adhered to Ac (characteristic time of 5.3 s), whereas Hc G186A, an α-1,3-glucan expressing strain, displayed much lower adhesion forces (characteristic time of 83.6 s). The specificity of our system was confirmed with addition of soluble β-1,3-glucan, which inhibited dramatically the adhesion of Hc G217B to Ac (characteristic time of 38,5 s). By indirect ELISA, the biotinylated extract of Ac showed higher binding to Hc G217B surface than Hc G186A, as similar results were observed when using Dectin-1-Fc. By interaction assays, association rates to Ac and RAW macrophages were twice higher for Hc G217B when compared to Hc G186A. Inhibitions with mannose, or its combinations with curdlan or laminarin demonstrated inhibitions higher than 50% during Ac and Hc G217B interaction. For RAW macrophages, the combinations mannose + laminarin and mannose + curdlan had inhibition of 64.4% and 51.5%, respectively, in the interaction with Hc G217B. The killing assay show that for A. castellanii, there was a decrease in the number of viable fungi when either laminarin and curdlan were added, which is similar to results observed with macrophages, suggesting the participation of this receptor for fungal entrance and survival within phagocytes. Proteomics identified several proteins with the capacity to bind β-1,3-glucans, including a membrane integral component (L8HDD6) displaying a legume lectin domain and also belonging to the Concanavalin A-like lectin/glucanase domain superfamily. By the demonstrated binding specificity of this receptor, our data reinforce other pathways of fungal recognition and suggests to a possible parallel or even divergent evolution, between A. castellanii and macrophages.

Dataset Information

Lutein, a Natural Carotenoid, Induces ?-1,3-Glucan Accumulation on the Cell Wall Surface of Fungal Plant Pathogens.

Publications

Lutein, a Natural Carotenoid, Induces α-1,3-Glucan Accumulation on the Cell Wall Surface of Fungal Plant Pathogens.

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