An unusual response regulator influences sporulation at early and late stages in Streptomyces coelicolor

State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100080, P. R. China, and John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, United Kingdom

^* To whom correspondence should be addressed. Email: tanhr{at}sun.im.ac.cn. keith.chater{at}bbsrc.ac.uk.

	Abstract

WhiI, a regulator required for efficient sporulation septation in the aerial mycelium of Streptomyces coelicolor, resembles response regulators of bacterial two-component systems, but lacks some conserved features of typical phosphorylation pockets. Four amino acids of the abnormal "phosphorylation pocket" were changed by site-directed mutagenesis. Unlike whiI null mutations, these point mutations did not interfere with sporulation septation, but had varying effects on spore maturation. Transcriptome analysis was used to compare gene expression in the wild-type strain, a D27A mutant (pale grey spores), a D69E mutant (wild-type spores), and a null mutant (white aerial mycelium, no spores) (a new variant of PCR targeting was used to introduce the point mutations into the chromosomal copy of whiI). The results revealed 45 genes that were affected by the deletion of whiI. Many of these showed increased expression in the wild-type at the time when aerial growth and development were taking place. About half of them showed reduced expression in the null mutant, and about half showed increased expression. Some, but not all, of these 45 genes were also affected by the D27A mutation, and a few by the D69E mutation. The results were consistent with a model in which WhiI acts differently at sequential stages of development. Consideration of the functions of whiI-influenced genes provides some insights into the physiology of aerial hyphae. Mutation of seven whiI-influenced genes revealed that three of them play roles in spore maturation.