Development and Media Regulate Alternative Splicing of a Methyltransferase Pre-mRNA in Monascus pilosus

Two alternatively spliced mRNAs (d and I-MpLaeA) of a methyltransferase gene (MpLaeA) were identified from Monascus pilosus IFO4520 and its mutant MK-1. Alternative splicing of the MpLaeA pre-mRNA occurred in the 5'-untranslated region (5-UTR). The alternative splicing patterns of MpLaeA were regulated by the fungal growth stage and the principal nutrients: that is, the short I-MpLaeA mRNA was a constitutive transcript at all growth stages and different carbon or nitrogen sources, but the glutamate and NaNO3 as main nitrogen source could up-regulate the long d-MpLaeA mRNA form. The long spliced 5-UTR of d-MpLaeA blocked GFP expression in Escherichia coli, suggesting that d-MpLaeA mRNA was an ineffective spliced mRNA. Downregulation of MpLaeA by transgenic antisense d-MpLaeA cDNA resulted in decreasing synthesis of monacolin K in M. pilosus. This suggested that the alternative splicing of MpLaeA mRNA might regulate the synthesis of monacolin K.