Abstract
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 α-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 α-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 α-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.
Highlights
Cell walls are essential for fungi to maintain their structure and to protect the cells from the environment
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
We found that recognition of a we found that recognition of a cutin monomer, 1,16-hexadecanediol, induced the accumulation cutin monomer, 1,16-hexadecanediol, induced the accumulation of α-1,3-glucan on the cell wall surface of α-1,3-glucan on the cell wall surface of M. oryzae by activating the cell wall integrity mitogenof M. oryzae by activating the cell wall integrity mitogen-activated protein kinase signal transduction activated protein kinase signal transduction pathway [4]
Summary
Cell walls are essential for fungi to maintain their structure and to protect the cells from the environment. The fungal cell wall is mainly composed of polysaccharides such as glucans, chitin/chitosan and mannan. The structural core of the cell wall is generally composed of branched β-1,3-glucan and chitin. This core is embedded in amorphous polysaccharides, e.g., α-1,3-glucan, and the composition of the amorphous polysaccharides may vary by fungal class/genus [1,2,3]. Intensive studies on medically important fungi have revealed that the composition and localization of cell wall polysaccharides change in response to environmental conditions such as temperature [3]. We have performed immunohistochemical studies of the organization of cell wall polysaccharides in phylogenetically distant plant pathogenic fungi: the ascomycetes Magnaporthe oryzae and Cochliobolus miyabeanus and the basidiomycete
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