Multifaceted Roles of chs Genes in Regulating Cell Growth, Mycelial Morphology, Monascus Pigments and Citrinin Biosynthesis in Monascus purpureus.

Chitin biosynthesis is intricately linked to the cellular growth and secondary metabolism of microorganisms. Our previous research has evaluated the role of the chs6 gene in modulating spore germination, mycelial morphology, and Monascus pigment biosynthesis in M. purpureus. However, the functions of other chs genes in theses contexts remain largely unexplored. The genes chsG, chsA, chs5, and chs2 were overexpressed in M. purpureus M183 to assess their diverse impacts on cell growth, Monascus pigments (MPs) and citrinin biosynthesis. The results indicated that chsG overexpression had the most significant effects, particularly enhancing MPs and citrinin synthesis while inhibiting transmembrane secretion. Morphological analysis revealed a substantial reduction in the length of mycelium of M. purpureus M183 following the overexpression of these chs genes. Furthermore, the surface of the mycelium pellets from these mutants displayed a more flocculent and roughened texture during SBF compared to M. purpureus M183. Notably, M. purpureus oe:chsG was characterized by conspicuously bolder mycelia, a denser cell wall, and darker cytoplasm. RT-qPCR results demonstrated that the chsG mRNA level increased by 11.9-fold in M. purpureus oe:chsG, and the individual overexpression of the genes chs5 and chsA triggered notable elevations in the chsG mRNA level. A comparative transcriptome analysis uncovered profound alterations in the expression patterns of genes associated with biosynthetic pathways of MPs, citrinin, fatty acid, and amino acid metabolism, as well as morphological regulation and growth, including the chitin and ergosterol biosynthetic pathways, MAPK signal pathway, global transcription factors, and peroxisomes.