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A broadly conserved fungal chorismate mutase targets the plant shikimate pathway to regulate salicylic acid production and other secondary metabolites

Summary

Fungal pathogens produce proteins called effectors that help them infect plants. This study discovered that a fungus called Sclerotinia sclerotiorum produces an effector that enters plant cells and travels to chloroplasts. Unlike similar effectors in other fungi, this protein increases the production of salicylic acid, a plant defense hormone, while reducing other protective compounds. This creates conditions favorable for the fungus to establish infection.

Background

Chorismate mutases (CMs) are effectors secreted by pathogens that hijack the plant shikimate pathway. While CMs have been primarily associated with biotrophic fungi, this study identifies a novel CM from the necrotrophic pathogen Sclerotinia sclerotiorum with broader distribution across diverse fungal lifestyles.

Objective

To characterize a secreted chorismate mutase from S. sclerotiorum (SsCM1) and determine how it manipulates the plant shikimate pathway differently from previously characterized CMs in biotrophic pathogens.

Results

SsCM1 is secreted and localizes to plant chloroplasts, unlike other characterized CMs. SsCM1 possesses both weak CM activity and IPL activity, increasing rather than decreasing salicylic acid levels. Structural analysis revealed SsCM1 shares greater similarity with bacterial isochorismate pyruvate lyase (PchB) than with the biotrophic fungal CM (Cmu1). SsCM1 interacts with plant chloroplast CMs.

Conclusion

SsCM1 represents a novel class of secreted CMs found in both necrotrophic and biotrophic fungi that manipulates the shikimate pathway through distinct mechanisms to increase SA levels while reducing antimicrobial compound biosynthesis, facilitating pathogenic success.
  • Published in:mBio,
  • Study Type:Experimental Research,
  • Source: PMID: 41114595
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