FIG. 1.

Proposed model for the FadA (G-protein) signal transduction pathway regulating growth, ST production, and conidiation in A. nidulans. FluG is involved in the synthesis of a small signal molecule participating in the positive regulation of FlbA, a GTPase-activating protein that negatively regulates FadA (the α-subunit of the heterotrimeric G protein), forming a Gα-Gβ-Gγ complex. Active FadA (separated from Gβ-Gγ subunits) positively regulates PkaA, inducing vegetative growth and inhibiting conidiation and ST production. FadA inhibition allows development and secondary metabolism production to occur (25). AflR and BrlA are specific transcription factors activating ST production and conidiation, respectively.