Plant lysin motif extracellular proteins are required for arbuscular mycorrhizal symbiosis

Huimin Yu, Fuxi Bai, Chuanya Ji, Zhengyan Fan, Jinying Luo, Bo Ouyang, Xiuxin Deng, Shunyuan Xiao, Ton Bisseling, Erik Limpens, Zhiyong Pan*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

5 Citations (Scopus)

Abstract

Arbuscular mycorrhizal fungi (AMF) can form a mutually beneficial symbiotic relationship with most land plants. They are known to secrete lysin motif (LysM) effectors into host root cells for successful colonization. Intriguingly, plants secrete similar types of LysM proteins; however, their role in plant microbe interactions is unknown. Here, we show that Medicago truncatula deploys LysM extracellular (LysMe) proteins to facilitate symbiosis with AMF. Promoter analyses demonstrated that three M.Truncatula LysMe genes MtLysMe1/2/3, are expressed in arbuscule-containing cells and those adjacent to intercellular hyphae. Localization studies showed that these proteins are targeted to the periarbuscular space between the periarbuscular membrane and the fungal cell wall of the branched arbuscule. M.Truncatula mutants in which MtLysMe2 was knocked out via CRISPR/Cas9-Targeted mutagenesis exhibited a significant reduction in AMF colonization and arbuscule formation, whereas genetically complemented transgenic plants restored wild-Type level AMF colonization. In addition, knocking out the ortholog of MtLysMe2 in tomato resulted in a similar defect in AMF colonization. In vitro binding affinity precipitation assays suggested binding of MtLysMe1/2/3 with chitin and chitosan, while microscale thermophoresis (MST) assays revealed weak binding of these proteins with chitooligosaccharides. Moreover, application of purified MtLysMe proteins to root segments could suppress chitooctaose (CO8)-induced reactive oxygen species production and expression of reporter genes of the immune response without impairing chitotetraose (CO4)-Triggered symbiotic responses. Taken together, our results reveal that plants, like their fungal partners, also secrete LysM proteins to facilitate symbiosis establishment.

Original languageEnglish
Article numbere2301884120
JournalProceedings of the National Academy of Sciences of the United States of America
Volume120
Issue number27
DOIs
Publication statusPublished - 27 Jun 2023

Keywords

  • arbuscular mycorrhizal symbiosis
  • chitin
  • immune response
  • LysMe proteins
  • Medicago truncatula

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