A short LysM protein with high molecular diversity from an arbuscular mycorrhizal fungus,Rhizophagus irregularis |
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Authors: | Alexa M. Schmitz Teresa E. Pawlowska Maria J. Harrison |
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Affiliation: | 1. Boyce Thompson Institute, 533 Tower Rd, Ithaca, NY, 14853, USA;2. School of Integrative Plant Science, Plant Pathology & Plant-Microbe Biology, Cornell University, Ithaca, NY, 14853, USA |
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Abstract: | Arbuscular mycorrhizal (AM) fungi form an intimate symbiosis with roots of more than 80% of land plants without eliciting a significant defense response, and how they do so is yet to be determined. Typically, plants mount a defense response upon sensing chitin in fungal walls, and to counteract this response, plant-pathogenic fungi secrete small effector proteins with chitin-binding LysM domains. In the AM fungus, Rhizophagus irregularis, a small, putatively-secreted LysM protein, which we refer to as RiSLM, is among the most highly expressed effector-like proteins during symbiosis. Here, we show that RiSLM expression is reduced during non-functional symbiosis with Medicago mutants, mtpt4-2 and vapyrin. We demonstrate that RiSLM can bind to both chitin and chitosan, and we model the protein-ligand interaction to identify possible binding sites. Finally, we have identified RiSLM homologs in five published R. irregularis isolate genomes and demonstrate that the gene is subject to a high rate of evolution and is experiencing positive selection, while still conserving putative function. Our results present important clues for elucidating a role for a LysM effector, RiSLM, in AM symbiosis. |
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Keywords: | Arbuscular mycorrhizal symbiosis LysM effector Fungi Chitin Positive selection AM arbuscular mycorrhizal LysM Lysin motif |
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