Transcription Factors AsMYB1 and AsMYB3 Regulate Betalain Biosynthesis in Aspergillus sydowii H-1

Betalains are nitrogen-containing pigments found only in Caryophyllales plants and a few Basidiomycetes; no Ascomycota species have been found to contain them. Here, global untargeted metabolomics analysis revealed that the violet pigment generated by the ascomycete Aspergillus sydowii H-1 under standard conditions of cultivation contains six distinct betalains compounds. Genetic analysis revealed tyrosinase (AsTYRs) and DOPA 4,5-dioxygenase (AsDODA1) as key enzymes essential for the synthesis of both the violet pigment and betalains. In addition, AsTYRs and AsDODA1 were found to regulate hyphal development and branching, mycelial pellet compactness, redox homeostasis, and stress responses, all of which had a significant impact on A. sydowii H-1 secondary metabolism. Crucially, two MYB transcription factors, AsMYB1 and AsMYB3, were identified to be negative regulators of violet pigment synthesis. Deletion of AsMYB1 or AsMYB3 boosted pigment yield by 6.7 and 7.3 times, respectively, and increased betalain accumulation, whereas overexpressing them completely eliminated pigment production. Yeast one-hybrid assays and luciferase reporter assays revealed AsMYB1 and AsMYB3 directly bind to the promoters of AsTYR1 and AsTYR2 to suppress the synthesis of betalains and the violet pigment. Our study reported the first betalain-producing ascomycete species and elucidated the molecular basis of its pigment regulation, providing valuable insights for the microbial synthesis of natural colorants.