Systematic analysis of the Myxococcus xanthus developmental gene regulatory network supports posttranslational regulation of FruA by C‐signaling

Abstract

Upon starvation Myxococcus xanthus undergoes 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 the dev operon. Leading up to and during the commitment period, dev mRNA 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 less dev mRNA than wild type at 30 h poststarvation, despite a similar level of MrpC and only 2-fold less FruA. Boosting the FruA level twofold in the C-signaling mutant had little effect on the dev mRNA level, and dev mRNA was not less stable in the C-signaling mutant. Neither did high cooperativity of MrpC and FruA binding upstream of the dev promoter 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.

Transcriptomic analysis of the Myxococcus xanthus FruA regulon, and comparative developmental transcriptomic analysis of two fruiting body forming species, Myxococcus xanthus and Myxococcus stipitatus

“…Two well-studied transcription factors, MrpC and FruA, that are essential for development are activated early during fruiting body formation [ 25 – 27 ]. FruA activation depends on the MrpC-dependent fruA transcription in response to starvation and the intercellular C-signal; subsequently MrpC and FruA act coordinately and are essential for the downstream gene regulatory changes responsible for fruiting body formation [ 25 , 28 – 31 ]. Ultimately these intra- and intercellular signals and transcription factors lead to the execution of this complex genetic program.…”

Regulation of late-acting operons by three transcription factors and a CRISPR-Cas component duringMyxococcus xanthusdevelopment

“…Specifically, we examined the effects of an insertion in fadI (55), a deletion of the entire nfsA-H operon (57), an insertion in exoC (58,61), and an insertion in exoL (63,64). As expected (29), the WT strain formed mounds by 18 h poststarvation (PS) and the mounds began to darken by 30 h (Fig. 2).…”

“…To quantify changes at the cellular level, we harvested samples from submerged culture and either treated the samples with glutaraldehyde to fix cells or left the samples untreated (29).…”

“…As noted above, FruA is present, but its level is about twofold lower in the csgA mutant than in the WT strain at 18-30 h (29). In the csgA mutant, FruA is expected to remain unactivated due to the absence of C-signaling (28,29). Therefore, it is possible that unactivated FruA negatively regulates the late-acting operons in the csgA mutant.…”

An amino‐terminal threonine/serine motif is necessary for activity of the Crp/Fnr homolog, MrpC and forMyxococcus xanthusdevelopmental robustness

“…A key downstream target is the transcription factor, FruA (Ogawa et al , ; Ueki and Inouye, ). FruA is an orphan response regulator that is thought to induce aggregation and then sporulation in response to C‐signaling, a cell–cell contact signal which increases in intensity as cells enter into aggregation centers (Sogaard‐Andersen and Kaiser, ; Ellehauge et al , ; Saha et al , ). Activated FruA and MrpC act separately and in combination to regulate a number of genes necessary for differentiation of cells inside aggregation centers into spores (Viswanathan et al , ; Mittal and Kroos, ; ; Son et al , ; Lee et al , ).…”