Altered flavin patterns in photobehavioral mutants of Phycomyces blakesleeanus

Area of Science:

• Mycology
• Photobiology
• Biochemistry

Background:

• Flavins are essential cofactors in the light-transduction pathways of the fungus Phycomyces blakesleeanus.
• Understanding flavin metabolism is crucial for elucidating the molecular mechanisms of phototropism and photogravitropism.

Purpose of the Study:

• To quantify flavin levels (riboflavin, FMN, FAD) in wild-type and mutant strains of P. blakesleeanus.
• To investigate the relationship between specific gene mutations (madA, madB, madC, madH) and altered flavin concentrations.
• To correlate endogenous flavin levels with photogravitropic responses.

Main Methods:

• Extraction of flavins from sporangiophores of P. blakesleeanus.
• High-Performance Liquid Chromatography (HPLC) with fluorescence detection for flavin identification and quantification.
• Comparison of flavin profiles between wild-type and various 'mad' (mutant) strains.

Main Results:

• Wild-type P. blakesleeanus contains riboflavin, flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD).
• Mutants with defective madA genes showed significantly reduced levels of all flavins (approx. 10-25% of wild-type).
• Mutations in madC and madB genes partially or fully restored flavin levels in madA mutants, indicating a regulatory role.
• A madH mutant exhibited elevated FMN and FAD levels.
• Photogravitropic thresholds were positively correlated with endogenous FMN and FAD concentrations.

Conclusions:

• The madA gene product is critical for maintaining normal flavin homeostasis in P. blakesleeanus.
• The madC and madB gene products act as positive regulators or restorers of flavin content, particularly in a madA mutant background.
• Flavin levels, specifically FMN and FAD, are directly linked to the light-sensing capabilities governing photogravitropism in this fungus.