A connection between stress and development in the multicellular prokaryote Streptomyces coelicolor A3(2)

Morphological changes leading to aerial mycelium formation and sporulation in the mycelial bacterium Streptomyces coelicolor rely on establishing dist inct patterns of gene expression in separate regions of the colony. sigma ( H) was identified previously as one of three paralogous sigma factors assoc iated with stress responses in S. coelicolor, Here, we show that sigH and t he upstream gene prsH (encoding a putative antisigma factor of sigma (H)) f orm an operon transcribed from two developmentally regulated promoters, sig Hp1 and sigHp2, While sigHp1 activity is confined to the early phase of gro wth, transcription of sigHp2 is dramatically induced at the time of aerial hyphae formation. Localization of sigHp2 activity using a transcriptional f usion to the green fluorescent protein reporter gene (sigHp2-egfp) showed t hat sigHp2 transcription is spatially restricted to sporulating aerial hyph ae in wild-type S. coelicolor, However, analysis of mutants unable to form aerial hyphae (bld mutants) showed that sigHp2 transcription and sigma (H) protein levels are dramatically upregulated in a bldD mutant, and that the sigHp2-egfp fusion was expressed ectopically in the substrate mycelium in t he bldD background, Finally, a protein possessing sigHp2 promoter-binding a ctivity was purified to homogeneity from crude mycelial extracts of S. coel icolor and shown to be BldD. The BldD binding site in the sigHp2 promoter w as defined by DNase I footprinting. These data show that expression of sigm a (H) is subject to temporal and spatial regulation during colony developme nt, that this tissue-specific regulation is mediated directly by the develo pmental transcription factor BldD and suggest that stress and developmental programmes may be intimately connected in Streptomyces morphogenesis.