Identification of Mga1, a G-protein α-subunit gene involved in regulating citrinin and pigment production in Monascus ruber M7

Abstract

The filamentous fungi Monascus spp., which have been used in traditional fermented food in Asia for centuries, are well-known producers of a group of bioactive metabolites that are widely used as food additives and nutraceutical supplements worldwide. However, its potential to produce the mycotoxin citrinin poses a threat to food safety. Here, a G-protein alpha-subunit-encoding gene, Mga1 (Monascus G-protein alpha-subunit 1), which encodes a protein showing a high degree of identity to Group I alpha-subunits of fungal heterotrimeric G-proteins, was cloned from Monascus ruber M7. An Mga1-disrupted strain was obtained by homologous recombination. The disruptant produced approximately nine times more citrinin and 71% more pigments than the wild-type strain M7, indicating that the G-protein alpha-subunit encoded by Mga1 is involved in a signal transduction pathway regulating citrinin and pigment biosynthesis in M. ruber M7.

mrflbA, encoding a putative FlbA, is involved in aerial hyphal development and secondary metabolite production in Monascus ruber M-7

“…For the determination of citrinin production, after the filtration described above, 10 mL of the filtrate was concentrated by a rotary vacuum evaporator and then the pellet was dissolved by 1 mL of methyl alcohol for HPLC (high-performance liquid chromatography) analysis. HPLC was performed following the method of Li et al (2010) with a slight modification. The prepared samples were filtered through a 0.2 mm filter and analyzed by HPLC performed on a Waters system (Waters, Milford, MA) fitted with a reverse-phase C18 column (Inertsil ODS-3, 250 mm  4.6 mm, 5 mm).…”

“…In this study, transcription levels of the Ga subunit encoding gene mga1 (Li et al 2010) and mrflbA in the wildtype strain and those in the mrflbA deletion strain were analyzed by real-time RT-PCR. The full-length cDNA of mga1 was cloned ( Fig 5A) and primers for real-time RT-PCR were designed according to the cDNA sequence of mga1.…”

“…Monascus spp. are the producers of red yeast rice (RYR), also called Hongqu, which have been widely used as food or food additives, folk medicine, as well as fermentation starters to brew rice wine and vinegar for many centuries in oriental countries (Lin et al 2008;Li et al 2010). Nowadays, a variety of bioactive metabolites, such as monacolins, gamma aminobutyric acid, pigment, and antioxidant (dimerumic acid) et al, have been identified and utilized world-wide (Aniya et al 2000;Su et al 2003); however, the isolation of citrinin, a kind of mycotoxin which might cause kidney and liver damage in humans, aroused controversy over the safety of Monascus spp.…”

“…Therefore, genes associated with these secondary metabolites synthesis attract extensive attention from researchers. In recent years, several genes involved in the biosynthesis of citrinin, monacolin K, and pigments (Shimizu et al 2005(Shimizu et al , 2007Chen et al 2008Chen et al , 2010Li et al 2010) have been cloned and analyzed, which made an important step forward in understanding the secondary metabolism in Monascus spp.…”

“…To investigate the role of mrflbA in the process of development and metabolism in M. ruber, we constructed the mrflbA deletion mutant for observing the phenotypes, detecting the production of pigments and citrinin, and analyzing the variation of transcription level for Ga subunit mga1 (accession number: FJ640858, Li et al 2010) of the mutant. To our knowledge, this is the first report describing RGS protein coding genes in Monascus spp., enhancing our understanding of the function of G protein signalling pathways in development and secondary metabolism in M. ruber.…”