Mutual suppression between mutations in the Dictyostelium greenbeard pathway restores wild-type development

ABSTRACT: The greenbeard allorecognition pathway of Dictyostelium discoideum is mediated by the polymorphic transmembrane proteins TgrB1 and TgrC1. TgrC1 is a ligand and TgrB1 is its receptor, and together they mediate allorecognition with accompanying altruism during the transition from unicellular to multicellular development. A genetic screen for suppressors of developmental defects in the non-compatible allotype TgrB1-C1 pathway revealed activating mutations in tgrB1 and inactivating mutations in rapgapB which encodes a regulator of the small GTPase protein RapA. Inactivation of either tgrB1, tgrC1, or rapgapB leads to developmental defects. However, surprisingly, the respective double-mutant strains rapgapB-tgrB1- and rapgapB-tgrC1- develop well and produce wild-type-like fruiting bodies. This mutual suppression could result from the induction of an alternative developmental pathway or restoration of the wild-type pathway, but morphological analyses alone could not resolve this question. Here we show that the mutual suppressors restore wild-type development. We used RNA-sequencing analyses to compare the transcriptomes of the wild type to those of six mutant strains and found that the single-gene mutations resulted in attenuated transcriptome progression over developmental time, whereas the double-gene mutation strains exhibited near wild-type transcriptomes. We also analyzed a strain that carries an activated tgrB1 allele in the wild type and found evidence for interactions between the activated and the resident alleles. Our findings suggest that tgrB1, tgrC1, and rapgapB are involved in a regulatory feedback pathway in which rapgapB negatively regulates tgrB1 and tgrC1 whereas tgrB1 and tgrC1 positively regulate rapgapB. These findings suggest that the D. discoideum greenbeard pathway interfaces with the central RapGAPB-RapA regulatory pathway, providing molecular insight into a mutual suppression mechanism in which combining two deleterious mutations leads to the restoration of wild-type behavior.

ORGANISM(S): Dictyostelium discoideum

PROVIDER: GSE279943 | GEO | 2024/12/06

REPOSITORIES: GEO