Expression Regulation Of Laccase Genes In Cerrena Unicolor

Fungal laccases comprise a type of ligninolytic enzymes;they have great potentials in various industrial applications with broad substrate specificity.Here,real-time quantitative PCR(qPCR)was used to explore expression regulation of eight laccase genes in a white-rot fungus Cerrena unicolor strain HYB07 with high laccase yields.1.Maximum laccase activity of 194.8 U/mL and 280.0 U/mL were obtained after fermentation for 4-5 d in PDY and YSJ media,respectively.Lac7 and Lac2 were most abundantly expressed at the early and late stages of fermentation in PDY medium,respectively.In YSJ medium,Lac7 transcript was the most abundant.2.Metal ions Cu2+ and Zn2+ promoted laccase production through increasing laccase gene transcription.Lac7 was up-regulated by Cu2+ and Zn2+,with Cu2+exerting the more significant effect.3.Nicotinic acid and vanillic acid reduced laccase production,whereas ABTS and guaiacol increased laccase production.In PDY medium,Lacl was most remarkably inhibited by nicotinic acid,and Lac2 was inhibited by vanillic acid.In YSJ medium,Lac1 and Lac6 transcription was induced by ABTS,and Lac4 was induced by guaiacol.4.Laccase production was highest in the medium with high carbon and nitrogen concentrations and lowest in low carbon and low nitrogen medium.Lac1 and Lac7 transcription was inhibited by both low carbon and low nitrogen conditions.Lac2 and Lac5 transcript levels were increased by low carbon condition.Lac3 and Lac4 mRNA synthesis was induced by low nitrogen condition.Lac6 was induced by both low carbon and low nitrogen conditions.5.Dextrin was the most suitable carbon source for HYB07 laccase production in YSJ medium.Replacing dextrin with glucose or sucrose resulted in transcriptional inhibition of most laccase genes.Expression of Lac2 and Lac5 was enhanced with glycerin,with Lac1 and Lac7 expression inhibited,resulting in lower laccase production.6.When the nitrogen source ammonium tartrate was replaced by malt extract,Lac3 transcript abundance was slightly increased,whereas Lac8 up-regulation was observed with yeast extract.When peptone was replaced by NH4NO3,Lac3 and Lac4 expression was significantly induced,along with suppressed Lac7 transcription,resulting in lower laccase production.The present project revealed that expression of HYB07 laccase was regulated by fermentation stage,metal ions,aromatic compounds as well as carbon and nitrogen sources and concentrations,which might be accounted for the putative regulatory elements in laccase promoters.Research findings can help elucidate physiological function of different laccase isoenzymes and provide theoretical foundation for laccase production and applications.