The AcGγ gene regulates cleistothecium development and flavor metabolism in dark tea

While the presence of Aspergillus cristatus cleistothecia (commonly known as "golden flowers") is a hallmark of Fuzhuan brick tea (FBT) quality, their specific role in flavor metabolism remains poorly understood. We hypothesized that the AcGγ gene acts as a core genetic regulator of cleistothecium development, and that the physical and enzymatic presence of these reproductive structures is associated with shifts in the secondary metabolite profiles related to dark tea flavor. To test this hypothesis, we compared the wild-type A. cristatus with AcGγ knockout (ΔAcGγ) and overexpression (OE::AcGγ) mutants using a controlled solid-state fermentation model and non-targeted LC-QTOF-MS metabolomics. Phenotypic analysis confirmed that AcGγ is strictly required for the formation of cleistothecia and ascospores, while also regulating colony morphology and growth rate. Metabolomic profiling revealed that the failure to form cleistothecia in the ΔAcGγ strain significantly altered the mycelial metabolome, particularly altering the abundance profiles of organic acids, organoheterocyclic compounds, and benzenoids. Furthermore, in the fermented tea matrix, AcGγ-mediated cleistothecium development was strongly associated with the bioconversion of key putative flavor-active components, markedly shifting the profiles of amino acids, flavonoids, and lipid-like molecules known to be associated with sweetness, bitterness, umami, and aroma. These findings support our hypothesis that AcGγ provides a genetic link between sexual development and altered flavor-related metabolic fluxes. Ultimately, this work provides a preliminary theoretical genetic and biochemical basis for future strain engineering and quality modulation of dark tea fermentation.