AvaR1, a Butenolide-Type Autoregulator Receptor in Streptomyces avermitilis, Directly Represses Avenolide and Avermectin Biosynthesis and Multiple Physiological Responses

Abstract

Avermectins are commercially important anthelmintic antibiotics produced by Streptomyces avermitilis. The homologous TetR-family transcriptional regulators AvaR1 and AvaR2 in this species were identified previously as receptors of avenolide, a novel butenolide-type autoregulator signal required for triggering avermectin biosynthesis. AvaR2 was found to be an important pleiotropic regulator in repression of avermectin and avenolide production and cell growth, whereas the regulatory role of AvaR1 remains unclear. Investigation of AvaR1 function in the present study showed that it had no effect on cell growth or morphological differentiation, but inhibited avenolide and avermectin production mainly through direct repression of aco (the key enzyme gene for avenolide biosynthesis) and aveR (the cluster-situated activator gene). AvaR1 also directly repressed its own gene (avaR1) and two adjacent homologous genes (avaR2 and avaR3). Binding sites of AvaR1 on these five target promoter regions completely overlapped those of AvaR2, leading to the same consensus binding motif. However, AvaR1 and AvaR2 had both common and exclusive target genes, indicating that they cross-regulate diverse physiological processes. Ten novel identified AvaR1 targets are involved in primary metabolism, stress responses, ribosomal protein synthesis, and cyclic nucleotide degration, reflecting a pleiotropic role of AvaR1. Competitive EMSAs and GST pull-down assays showed that AvaR1 and AvaR2 competed for the same binding regions, and could form a heterodimer and homodimers, suggesting that AvaR1 and AvaR2 compete and cooperate to regulate their common target genes. These findings provide a more comprehensive picture of the cellular responses mediated by AvaR1 and AvaR2 regulatory networks in S. avermitilis.

Regulation of Antibiotic Production by Signaling Molecules in Streptomyces

“…CSR activator gene sanG and biosynthetic genes of the sanF-X operon (Figure 2; Pan et al, 2009;Wang et al, 2018). Of the three GBL receptors in S. avermitilis, AvaR1 acts as an avenolide receptor to control avenolide and avermectin production by directly repressing the transcription of aco, aveR, its own gene and the other two GBL receptor homologous genes (avaR2 and avaR3) (Figure 3; Zhu et al, 2017). ScbR2, JadR2, AvaR2 and SabR2 were identified as pseudo GBL receptors (Xu et al, 2010;Zhu et al, 2016;Wang et al, 2018), and the roles of these pseudo GBL receptors in the regulation of antibiotic biosynthesis will be discussed in a subsequent section.…”

SbbR/SbbA, an Important ArpA/AfsA-Like System, Regulates Milbemycin Production in Streptomyces bingchenggensis

“…In S. ansochromogenes , SabR binds to the sequences (from nt -64 to -29 relative to the tsp of sanG ) adjacent to or overlapping partially with the -35 element and positively regulates sanG transcription ( He et al, 2010 ). There are also exceptions, AvaR1, the ArpA homolog from S. avermitilis , protects two regions (regions from nt -262 to -233 and nt -223 to -193) far upstream of AveR (the cluster-situated activator of avermectins) and acts as a repressor, but not an activator ( Zhu et al, 2017 ); one of the two binding sites (nt -222 to -244 and nt -3 to -35 relative to the cpkO tsp) of ScbR from S. coelicolor is also far away from cpkO promoter and ScbR is a repressor of cpkO ( Takano et al, 2005 ). These examples complicate the regulatory mechanisms exerted by GBL receptor homologs.…”

Organic Peroxide-Sensing Repressor OhrR Regulates Organic Hydroperoxide Stress Resistance and Avermectin Production in Streptomyces avermitilis

“…OhrR thus represses avermectin production by controlling the expression of pathway-specific activator gene aveR . Several transcription factors have been shown to control avermectin production through direct regulation of aveR expression; these include phosphate metabolism regulator PhoP, pseudo γ-butyrolactone receptor homolog AvaR2, GBL receptor AvaR1, and Redox-sensing regulator Rex ( Yang et al, 2015 ; Zhu et al, 2016 , 2017 ; Liu et al, 2017 ). The present results demonstrate that avermectin production is directly regulated by OhrR.…”