Cloning and functional analysis of the Gβ gene Mgb1 and the Gγ gene Mgg1 in Monascus ruber.

The ascomycetous fungus Monascus ruber is one of the most well-known species widely used to produce Monascus-fermentation products for natural food colorants and medicine. Our previous research on the Gα subunit Mga1 and the regulator of G protein signaling MrflbA indicated that heterotrimeric G protein signaling pathways were involved in aspects of growth, sporulation and secondary metabolite production in M. ruber. To better understand the G protein signaling pathways in this fungus, a Gβ subunit gene (Mgb1) and a GΓ subunit gene (Mgg1) were cloned and investigated in the current study. The predicted Mgb1 protein consisted of 353 amino acids and Mgg1 consisted of 94 amino acids, sharing marked similarity with Aspergillus Gβ and GΓ subunits, respectively. Targeted deletion (Δ) of Mgb1 or Mgg1 resulted in phenotypic alterations similar to those resulting from ΔMga1, i.e., restricted vegetative growth, lowered asexual sporulation, impaired cleistothecial formation, and enhanced citrinin and pigment production. Moreover, deletion of Mgg1 suppressed the defects in asexual development and in biosynthesis of citrinin and pigment caused by the absence of MrflbA function. These results provide evidence that Mgb1 and Mgg1 form a functional GβΓ dimer and the dimer interacts with Mga1 to mediate signaling pathways, which are negatively controlled by MrflbA, for growth, reproduction and citrinin and pigment biosynthesis in M. ruber.