Identification of a gene involved in polysaccharide export as a transcription target of FruA, an essential factor for...

Fruiting body development in Myxococcus xanthus is a multicellular event that is coordinated by exchanging intercellular signals. FruA is a transcription factor essential for fruiting body development and is thought to play a key role in the C-signal pathway. Here we present the first identification of a gene regulated by FruA. The gene was isolated from a genomic library via in vitro selection in a DNA binding assay by using the DNA-binding domain of FruA tagged with His(8) at the C-terminal end (FruA-DBD-H(8)). The gene, named fdgA (FruA-dependent gene A), encodes a protein homologous to the outer-membrane auxiliary family protein involved in the polysaccharide export system. FruA-DBD-H(8) bound the upstream promoter region of the fdgA gene from nucleotide -89 to nucleotide -64 with respect to the transcription initiation site, which was required for the induction of fdgA expression during development. fdgA mRNA induced during development was absent in a fruA deletion strain. The deletion of fdgA resulted in defective fruiting body formation and reduced sporulation efficiency (1% that of the parent strain). Moreover, FruA was required for the developmental expression of sasA, which is also involved in the biosynthesis of the lipopolysaccharide O-antigen and is required for fruiting body development. Furthermore, the expression of both fdgA and sasA was partially dependent on the C-signal. These findings expand our understanding of the signal transduction pathway mediated by FruA during development in M. xanthus.