Strobilurin biosynthesis in Basidiomycete fungi

Area of Science:

• Biochemistry
• Mycology
• Agricultural Science

Background:

• Strobilurins, derived from fungi, are the basis for β-methoxyacrylate agricultural fungicides.
• The precise biosynthesis of strobilurins has been poorly understood at the molecular level.

Purpose of the Study:

• To elucidate the molecular mechanisms and genetic basis of strobilurin biosynthesis in fungi.
• To identify the key enzymes and pathways involved in creating the fungicidal β-methoxyacrylate structure.

Main Methods:

• Genome sequencing of two strobilurin-producing fungi.
• Heterologous expression of a identified biosynthetic gene cluster (stpks1) in Aspergillus oryzae.
• Biochemical analysis and gene augmentation to identify essential enzymes and intermediates.

Main Results:

• A novel biosynthetic gene cluster encoding a highly reducing polyketide synthase with unique domains was identified.
• Expression of stpks1 and supplementation with a benzoyl coenzyme A (CoA) analogue yielded prestrobilurin A, revealing a new benzoyl CoA route.
• Reconstruction of the gene cluster and addition of str9 (an FAD-dependent oxygenase) successfully produced prestrobilurin A and demonstrated the key oxidative rearrangement for the β-methoxyacrylate toxophore.
• Two methyltransferases were found to be essential for completing the strobilurin synthesis.

Conclusions:

• The study reveals the complete biosynthetic pathway for strobilurins, including the formation of the β-methoxyacrylate toxophore.
• This discovery provides a foundation for understanding fungal secondary metabolism and for engineering novel fungicides.