Nigericin is a polyether antibiotic with potent antibacterial, antifungal, antimalarial and anticancer activity. NigR, the only regulator in the nigericin biosynthetic gene cluster in Streptomyces malaysiensis F913, was identified as a SARP family regulator. Disruption of nigR abolished nigericin biosynthesis, while complementation of nigR restored nigericin production, suggesting that NigR is an essential positive regulator for nigericin biosynthesis. Overexpression of nigR in Streptomyces malaysiensis led to significant increase in nigericin production compared to the wild-type strain. Nigericin production in the overexpression strain was found to reach 0.56 g/L, which may be the highest nigericin titer reported to date. Transcriptional analysis suggested that nigR is required for the transcription of structural genes in the nig gene cluster; quantitative RT-PCR analysis revealed that the expression of structural genes was upregulated in the nigR overexpression strain. Our study suggested that NigR acts in a positive manner to modulate nigericin production by activating transcription of structural genes and provides an effective strategy for scaling up nigericin production.

Isopentenyl diphosphate isomerase (IPPI) is a key enzyme catalyzing the interconversion between isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP), two isoprenyl C5 units that are precursors for terpenoid biosynthesis. Previous study has identified two IPPIs, namely AaIPPI1 and AaIPPI2 from Artemisia annua, and revealed the positive role of AaIPPI1 in regulating the biosynthesis of terpenoids. However, the role of AaIPPI2 in regulating terpenoid biosynthesis remains to be clarified. In this study, we explored the contribution of AaIPPI2 to terpenoid biosynthesis in Artemisia annua. Overexpression of AaIPPI2 in A. annua significantly enhanced the contents of diverse monoterpenes and sesquiterpenes. Suppression of AaIPPI2 by RNA interference (RNAi) in A. annua markedly reduced the biosynthesis of these sesquiterpenes, but only caused a modest decrease in several monoterpenes’ levels with no change in other monoterpenes’ levels, suggesting that AaIPPI2 plays a lesser part in the regulation of monoterpenes biosynthesis in plastids compared to AaIPPI1. Taken together, these results demonstrate that AaIPPI2 plays a positive role in regulating the biosynthesis of terpenoids. Our findings enhanced the understanding of the distinction between the roles of the two IPPIs in the regulation of terpenoid biosynthesis in A. annua and provided candidate genes for optimizing terpene production in plants.