Krall, E. G. | Search bioRxiv

bioRxiv2024

SWR1 is recruited to activated ABA response genes to maintain gene body H2A.Z in Arabidopsis thaliana

The histone variant H2A.Z is important for transcriptional regulation across eukaryotes, where it can alternately promote or repress transcription. In plants, actively transcribed genes show H2A.Z enrichment in nucleosomes immediately downstream of the transcription start site (TSS), while silent genes show H2A.Z enrichment across the gene body. Previous work showed that silent genes responsive to temperature and far-red light lose gene body H2A.Z upon activation, but whether H2A.Z loss is generally required for transcription is not clear. We profiled H2A.Z and components of its deposition complex, SWR1, before and after treating Arabidopsis thaliana with the hormone abscisic acid (ABA). Our results show that transcribed genes with TSS-enriched H2A.Z have high SWR1 binding at steady-state, indicating continuous replacement of H2A.Z, while silent genes with gene body H2A.Z show lower SWR1 binding. Surprisingly, upon ABA treatment, thousands of previously silent genes activate, coincident with recruitment of SWR1 and retention of gene body H2A.Z enrichment. We also found that the SWR1-interacting protein MBD9 is not required for SWR1 recruitment to activated genes. These results provide new insights into the relationship between H2A.Z and transcription and the mechanics of H2A.Z targeting to chromatin.

plant biology↗

bioRxiv2019

RstA Regulation of Clostridioides difficile Toxin Production and Sporulation in Phenotypically Diverse Strains

The anaerobic spore-former, Clostridioides difficile, causes significant diarrheal disease in humans and other mammals. Infection begins with the ingestion of dormant spores which subsequently germinate within the host gastrointestinal tract. Here, the vegetative cells proliferate and secrete two exotoxins, TcdA and TcdB, which cause disease symptoms. Although spore formation and toxin production are critical for C. difficile pathogenesis, the regulatory links between these two physiological processes are not well understood and are strain-dependent. Previously, we identified a conserved C. difficile regulator, RstA, that promotes sporulation initiation through an unknown mechanism and directly and indirectly represses toxin gene transcription in the historical isolate, 630{Delta}erm. To test whether perceived strain-dependent differences in toxin production and sporulation are mediated by RstA, we created an rstA mutant in the epidemic 027 ribotype strain, R20291. RstA affects sporulation and toxin gene expression similarly in R20291, although more robust regulatory effects are observed in this strain than in 630{Delta}erm. Reporter assays measuring transcriptional regulation of tcdR, the sigma factor essential for toxin gene expression, identified sequence-dependent effects influencing repression by RstA and CodY, a global nutritional sensor, in four diverse C. difficile strains. We provide evidence that RstA contributes to tcdR bistability in R20291 by biasing cells to a toxin-OFF state. Finally, sequence-dependent and strain-dependent differences were evident in RstA negative autoregulation of rstA transcription. Our data establish RstA as an important regulator of C. difficile virulence traits, and implicate RstA as a contributor to the variety of sporulation and toxin phenotypes observed in distinct isolates.\n\nIMPORTANCETwo critical traits of Clostridioides difficile pathogenesis are the production of toxins, which cause disease symptoms, and the formation of spores, which permit survival outside of the gastrointestinal tract. The multifunctional regulator, RstA, promotes sporulation and prevents toxin production in the historical strain, 630{Delta}erm. Here, we show that RstA functions similarly in an epidemic isolate, R20291, although strain-specific effects on toxin and rstA expression are evident. Our data demonstrate that sequence-specific differences within the promoter for the toxin regulator, TcdR, contribute to regulation of toxin production by RstA and CodY. These sequence differences account for some of the variability in toxin production among isolates, and may allow strains to differentially control toxin production in response to a variety of signals.

microbiology↗