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Phytohormones and volatile organic compounds, like geosmin, in the ectomycorrhiza of Tricholoma vaccinum and Norway spruce (Picea abies)

Summary

This research examines how a fungus (Tricholoma vaccinum) and spruce tree communicate through chemical signals. The fungus produces unique compounds including geosmin (the earthy smell of soil after rain), limonene (lemon scent), and plant hormones. These chemicals help the fungus and tree establish their beneficial partnership by affecting how the fungus grows and branches around the tree roots. The findings show that these chemical signals are crucial for successful formation of the mycorrhizal relationship.

Background

The ectomycorrhizospheric habitat contains diverse organisms including the host plant, mycorrhizal fungi, and rhizospheric microorganisms. Different signaling molecules including phytohormones and volatile organic compounds may influence ectomycorrhizal symbiosis. This study investigated the potential of the basidiomycete Tricholoma vaccinum to produce communication molecules for interaction with Norway spruce.

Objective

To investigate the production of volatile organic compounds and phytohormones by Tricholoma vaccinum, identify potential biosynthesis genes, investigate their expression via RNA-Seq, and determine the effects of these compounds on mycorrhizal establishment and functioning.

Results

T. vaccinum released volatiles including limonene, β-barbatene, and geosmin, along with phytohormones (ethylene, salicylic acid, abscisic acid, jasmonates). The geosmin biosynthesis gene ges1 was identified and showed up-regulation during mycorrhiza. Salicylic and abscisic acid altered hyphal branching in concentration-dependent manner. Phytohormones were detected for the first time in natural ectomycorrhizospheric soil and root exudates.

Conclusion

T. vaccinum produces multiple signaling molecules that contribute to interkingdom communication in ectomycorrhizal symbiosis. The regulation of phytohormones and VOCs, particularly geosmin and phytohormones affecting hyphal branching, suggests these compounds play important roles in mycorrhiza establishment and functioning. A well-balanced level of mycorrhizospheric phytohormones is necessary for extensive branching required for mycorrhiza establishment.
  • Published in:Mycorrhiza,
  • Study Type:Experimental Study,
  • Source: PMID: 33210234
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