A genetic link between light response and multicellular development in the bacterium Myxococcus xanthus.

Abstract

The Gram-negative bacterium Myxococcus xanthus responds to blue light by producing carotenoid pigments (Car + phenotype). Genes for carotenoid synthesis lie at two unlinked chromosomal sites, the carC and the carBA operon, but are integrated in a single "light regulon" by the action of common trans-acting regulatory elements. Three known regulatory genes are grouped together at the (light-inducible) carORS operon. By screening the Car phenotype of a large collection of transposon-induced mutants, we have identified a new car locus that has been named carD (carD1 for the mutant allele). The carD gene product plays a critical role in the light regulon, as it is required for activation of the carQRS and carC promoters by blue light. The carD1 mutant is impaired in the (starvation-induced) developmental process that allows M. xanthus cells both to form multicellular fruiting bodies and to sporulate. Our results indicate that the carD gene product is also required for the expression of a particular set of development-specific genes that are normally activated through the action of intercellular signals.

Domain Architecture of a High Mobility Group A-type Bacterial Transcriptional Factor

“…The C-terminal HMGA-like part of CarD would be similarly malleable to such conformational and so functional alterations. Moreover, like HMGA proteins, CarD is also a multifunctional regulator being involved in the distinct processes of carotenogenesis and multicellular development in M. xanthus (20). Work currently in progress in this laboratory has also underscored the involvement of CarD in processes other than carotenogenesis and fruiting body development.…”

“…22). Mutations in carD prevent fruiting body formation and block the expression of several developmentally activated genes (20). Thus CarD, like mammalian HMGA proteins, is recruited by distinct gene regulatory circuits in vivo.…”

“…Protein CarD is involved in regulating at least two distinct processes in M. xanthus (20). It is required for the expression of two different sets of genes that form part of a complex network regulating light-induced carotenogenesis, "the light regulon" (reviewed in Ref.…”

A Repressor-Antirepressor Pair Links Two Loci Controlling Light-induced Carotenogenesis in Myxococcus xanthus

“…The released CarQ is then free to activate transcription from the crtI promoter (P I ). CarQ, in conjunction with CarD and the histone-like protein IhfA, also promotes transcription from its own promoter (P QRS ), leading to increased production in the light of the three proteins encoded in the operon (10,13,14). Photoinduction of the structural genes in the carB operon depends on a different set of regulatory proteins: CarS, encoded by the third gene of the carQRS operon (13), and CarA, produced independently of light from an unlinked operon (Fig.…”

Operator Design and Mechanism for CarA Repressor-mediated Down-regulation of the Photoinducible carB Operon in Myxococcus xanthus

“…Once liberated, CarQ up-regulates expression of car-QRS and crtI (18). In this, CarQ is aided by the high mobility group A-type protein CarD (23)(24)(25)(26) and the histone-like protein IhfA (integration host factor ␣ subunit) (27). The photo-induced expression of the carB operon is regulated by CarA, which is produced independently of light from an adjacent operon, and by CarS (28,29).…”