Response Regulator Heterodimer Formation Controls a Key Stage in Streptomyces Development

Abstract

The orphan, atypical response regulators BldM and WhiI each play critical roles in Streptomyces differentiation. BldM is required for the formation of aerial hyphae, and WhiI is required for the differentiation of these reproductive structures into mature spores. To gain insight into BldM function, we defined the genome-wide BldM regulon using ChIP-Seq and transcriptional profiling. BldM target genes clustered into two groups based on their whi gene dependency. Expression of Group I genes depended on bldM but was independent of all the whi genes, and biochemical experiments showed that Group I promoters were controlled by a BldM homodimer. In contrast, Group II genes were expressed later than Group I genes and their expression depended not only on bldM but also on whiI and whiG (encoding the sigma factor that activates whiI). Additional ChIP-Seq analysis showed that BldM Group II genes were also direct targets of WhiI and that in vivo binding of WhiI to these promoters depended on BldM and vice versa. We go on to demonstrate that BldM and WhiI form a functional heterodimer that controls Group II promoters, serving to integrate signals from two distinct developmental pathways. The BldM-WhiI system thus exemplifies the potential of response regulator heterodimer formation as a mechanism to expand the signaling capabilities of bacterial cells.

Interaction of the RcsB Response Regulator with Auxiliary Transcription Regulators in Escherichia coli

“…BldM homodimers activate transcription of group I genes required for early stages of development, whereas BldM-WhiI heterodimers regulate expression of group II genes involved in the late stages of development. Correspondingly, the BldM consensus DNA-binding site is palindromic, whereas the BldM-WhiI consensus DNA-binding site is asymmetric with one half-site matching the BldM consensus sequence (19). This example demonstrates that heterodimerization of a response regulator is a means to control a developmental program (19).…”

“…Correspondingly, the BldM consensus DNA-binding site is palindromic, whereas the BldM-WhiI consensus DNA-binding site is asymmetric with one half-site matching the BldM consensus sequence (19). This example demonstrates that heterodimerization of a response regulator is a means to control a developmental program (19).…”

“…Currently, it has been described for BldM and WhiI in the filamentous bacteria Streptomyces (19). BldM and WhiI are atypical and orphan response regulators, which are presumably not phosphorylated by cognate sensor kinases.…”

“…Thus, there is a dual control of RcsB activity, by phosphorylation via the Rcs phosphorelay and by interaction with auxiliary partners all belonging to the FixJ/NarL family of transcriptional regulators. To date, heterodimerization of bacterial response regulators in addition to RcsB has only been described for BldM and WhiI in the filamentous bacteria Streptomyces (19).…”

Fluorescence Time-lapse Imaging of the Complete <em>S. venezuelae</em> Life Cycle Using a Microfluidic Device

“…By growing Streptomyces in a microfluidic device connected to a fluorescence widefield microscope (Figure 2), we are now able to monitor germination, vegetative growth and sporulation septation over a time period of up to 30 hr. This is greatly facilitated by the use of the new model organism Streptomyces venezuelae because it sporulates to near completion in submerged culture and thereby overcomes the limitation of the classical model species S. coelicolor, which sporulates only on solid media [16][17][18][19][20] . To help visualize vegetative growth and sporulation, we co-express fluorescently tagged versions of the cell polarity marker DivIVA and the key cell division protein FtsZ.…”