Global Effects of the Developmental Regulator BldB in Streptomyces venezuelae.

In , the Bld (Bald) regulators control formation of the reproductive aerial hyphae. The functions of some of these regulators have been well characterized, but BldB has remained enigmatic. In addition to the gene itself, Streptomyces venezuelae has 10 paralogs of that sit next to paralogs of and . Transcriptome sequencing (RNA-seq) revealed that loss of BldB function causes the dramatic transcriptional upregulation of the paralogs and a novel inhibitor of sporulation, , and that cooverexpression of just two of these genes, and , was sufficient to recapitulate the mutant phenotype. Further RNA-seq analysis showed that the transcription factor WhiJ9 is required for the activation of seen in the mutant, and biochemical studies showed that WhiJ9 mediates the activation of expression by binding to direct repeats in the intergenic region. BldB and BldB9 hetero-oligomerize, providing a potential link between BldB and the locus. This work greatly expands our overall understanding of the global effects of the BldB developmental regulator. To reproduce and disperse, the filamentous bacterium develops specialized reproductive structures called aerial hyphae. The formation of these structures is controlled by the (bald) genes, many of which encode transcription factors whose functions have been characterized. An exception is BldB, a protein whose biochemical function is unknown. In this study, we gain insight into the global effects of BldB function by examining the genome-wide transcriptional effects of deleting . We identify a small set of genes that are dramatically upregulated in the absence of BldB. We show that their overexpression causes the phenotype and characterize a transcription factor that mediates the upregulation of one of these target genes. Our results provide new insight into how BldB influences development.