A short LysM protein with high molecular diversity from an arbuscular mycorrhizal fungus, Rhizophagus irregularis

• Published in: Mycoscience Vol. 60; no. 1; pp. 63 - 70
• Main Authors: Schmitz, Alexa M., Pawlowska, Teresa E., Harrison, Maria J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.2019; The Mycological Society of Japan
• Subjects: Arbuscular mycorrhizal symbiosis; binding sites; Chitin; chitosan; embryophytes; evolution; Fungi; genes; LysM effector; Medicago; mutants; mycorrhizal fungi; plant pathogenic fungi; Positive selection; proteins; Rhizophagus irregularis; roots; vesicular arbuscular mycorrhizae; Fungi; LysM effector; LysM; Positive selection; Chitin; AM; Arbuscular mycorrhizal symbiosis
• ISSN: 1340-3540; 1618-2545; 1618-2545
• DOI: 10.1016/j.myc.2018.09.002

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. •A small secreted LysM protein, named RiSLM, was cloned from Rhizophagus irregularis.•Expression of RiSLM is reduced during non-functional symbiosis.•RiSLM binds to chitin and chitosan.•RiSLM is present in genomes of other R. irregularis isolates.•RiSLM has high nucleotide diversity and experiences diversifying selection.