Systematic analysis of theMyxococcus xanthusdevelopmental gene regulatory network supports posttranslational regulation of FruA by C-signaling

Abstract

SummaryUpon starvationMyxococcus xanthusundergoes multicellular development. Rod-shaped cells move into mounds in which some cells differentiate into spores. Cells begin committing to sporulation at 24-30 h poststarvation, but the mechanisms governing commitment are unknown. FruA and MrpC are transcription factors that are necessary for commitment. They bind cooperatively to promoter regions and activate developmental gene transcription, including that of thedevoperon. Leading up to and during the commitment period,devmRNA increased in wild type, but not in a mutant defective in C-signaling, a short-range signaling interaction between cells that is also necessary for commitment. The C-signaling mutant exhibited ∼20-fold lessdevmRNA than wild type at 30 h poststarvation, despite a similar level of MrpC and only twofold less FruA. Boosting the FruA level twofold in the C-signaling mutant had little effect on thedevmRNA level, anddevmRNA was not less stable in the C-signaling mutant. Neither did high cooperativity of MrpC and FruA binding upstream of thedevpromoter explain the data. Rather, our systematic experimental and computational analyses support a model in which C-signaling activates FruA at least ninefold posttranslationally in order to commit a cell to spore formation.