Abstract
In the root endophyte Serendipita indica, several lectin-like members of the expanded multigene family of WSC proteins are transcriptionally induced in planta and are potentially involved in β-glucan remodeling at the fungal cell wall. Using biochemical and cytological approaches we show that one of these lectins, SiWSC3 with three WSC domains, is an integral fungal cell wall component that binds to long-chain β1-3-glucan but has no affinity for shorter β1-3- or β1-6-linked glucose oligomers. Comparative analysis with the previously identified β-glucan-binding lectin SiFGB1 demonstrated that whereas SiWSC3 does not require β1-6-linked glucose for efficient binding to branched β1-3-glucan, SiFGB1 does. In contrast to SiFGB1, the multivalent SiWSC3 lectin can efficiently agglutinate fungal cells and is additionally induced during fungus-fungus confrontation, suggesting different functions for these two β-glucan-binding lectins. Our results highlight the importance of the β-glucan cell wall component in plant-fungus interactions and the potential of β-glucan-binding lectins as specific detection tools for fungi invivo.
Highlights
Plant root-associated fungi thrive in challenging and rapidly changing environments
Because WSC proteins were proposed to bind to the cell wall (CW) of fungi and SiWSC3 harbors a predicted secretion signal peptide, we hypothesized that SiWSC3 may localize to the CW of S. indica
To study its subcellular localization the SiWSC3 gene was expressed as fusion with a C-terminal GFP tag under the control of the S. indica FGB1 promoter which is highly active in planta and in complex medium (CM) but less active in other axenic media (Wawra et al, 2016)
Summary
Plant root-associated fungi thrive in challenging and rapidly changing environments. Their ability to colonize their hosts depends, among others, on their capacity to remodel the cell surface to withstand biotic and abiotic stresses and to limit plant immune recognition. CW-derived polysaccharides, such as chitin and bglucans, are potent elicitors of plant immune responses and their detection needs to be prevented while maintaining CW integrity for successful colonization (Rovenich et al, 2016; Geoghegan et al, 2017; Latge et al, 2017; Hopke et al, 2018). To avoid recognition of CW-derived polysaccharides and to limit stimulation of plant defense responses, fungi have evolved different strategies such as CW remodeling, masking, shielding and manipulation of glycaninduced host defense signaling
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