Deletion of the Response Regulator PhoP Accelerates the Formation of Aerial Mycelium and Spores in Actinosynnema pretiosum

PhoPR is an important two-component signal transduction system (TCS) for microorganisms to sense and respond to phosphate limitation. Although the response regulator PhoP controls morphological development and secondary metabolism in various species, the function of PhoP in remains unclear. In this study, we showed that PhoP significantly represses the morphological development of the X47 strain. Production of aerial mycelium and spore formation occurred much earlier in the ΔphoP strain than in X47 during growth on ISP2 medium. Transcription analysis indicated that 222 genes were differentially expressed in ∆phoP compared to strain X47. Chemotaxis genes ( , , , and ); flagellum biosynthesis and motility genes ( , , , , and ); and differentiation genes ( and ) were significantly upregulated in ∆phoP. Gel-shift analysis indicated that PhoP binds to the promoters of , , and genes, and PHO box-like motif with the 8-bp conserved sequence GTTCACGC was identified. The transcription of / of X47 strain was induced at low phosphate concentration. Our results demonstrate that PhoP is a negative regulator that controls the morphological development of X47 by repressing the transcription of differentiation genes.