Figure 7.

A quorum signaling pathway linking environmental sensing to morphogenesis and entry into stationary phase in S. cerevisiae. Aromatic alcohols are autosignaling molecules capable of stimulating morphogenesis in Saccharomyces by elevating the level of Flo11p through a Tpk2p-dependent mechanism. The production of aromatic alcohols is tightly controlled by environmental conditions. High ammonium represses their production by inhibiting the transcription of key genes in the biosynthesis pathway (such as ARO9 and ARO10), whereas low ammonium activates it. Cell density also controls the production of aromatic alcohols. High density stimulates the production by activating the expression of ARO9 and ARO10, whereas low cell density inhibits it. Moreover, the production of aromatic alcohols is under positive feedback control by tryptophol. Both the cell density-dependent and feedback regulation require transcription factor Aro80p. Aromatic alcohols also regulate the expression of many stationary-phase genes, suggesting a potential role in modulating the entry of Saccharomyces cells into stationary phase.