Populus MYC2 orchestrates root transcriptional reprogramming of defence pathway to impair Laccaria bicolor ectomycorrhizal development

New Phytol. 2024 Apr;242(2):658-674. doi: 10.1111/nph.19609. Epub 2024 Feb 20.

Abstract

The jasmonic acid (JA) signalling pathway plays an important role in the establishment of the ectomycorrhizal symbiosis. The Laccaria bicolor effector MiSSP7 stabilizes JA corepressor JAZ6, thereby inhibiting the activity of Populus MYC2 transcription factors. Although the role of MYC2 in orchestrating plant defences against pathogens is well established, its exact contribution to ECM symbiosis remains unclear. This information is crucial for understanding the balance between plant immunity and symbiotic relationships. Transgenic poplars overexpressing or silencing for the two paralogues of MYC2 transcription factor (MYC2s) were produced, and their ability to establish ectomycorrhiza was assessed. Transcriptomics and DNA affinity purification sequencing were performed. MYC2s overexpression led to a decrease in fungal colonization, whereas its silencing increased it. The enrichment of terpene synthase genes in the MYC2-regulated gene set suggests a complex interplay between the host monoterpenes and fungal growth. Several root monoterpenes have been identified as inhibitors of fungal growth and ECM symbiosis. Our results highlight the significance of poplar MYC2s and terpenes in mutualistic symbiosis by controlling root fungal colonization. We identified poplar genes which direct or indirect control by MYC2 is required for ECM establishment. These findings deepen our understanding of the molecular mechanisms underlying ECM symbiosis.

Keywords: Laccaria bicolor; MYC2 transcription factor; ectomycorrhiza; plant defence; plant–microbe interactions; poplar; symbiosis; terpenes.

MeSH terms

  • Cyclopentanes*
  • Laccaria* / genetics
  • Monoterpenes / metabolism
  • Mycorrhizae* / genetics
  • Oxylipins*
  • Plant Roots / metabolism
  • Populus* / metabolism
  • Symbiosis / genetics
  • Transcription Factors / genetics
  • Transcription Factors / metabolism

Substances

  • Transcription Factors
  • jasmonic acid
  • Monoterpenes
  • Cyclopentanes
  • Oxylipins

Supplementary concepts

  • Laccaria bicolor