Project description:In the model green alga Chlamydomonas (Chlamydomonas reinhardtii), the synthesis of several chloroplast-encoded photosynthetic subunits is feedback-regulated by the assembly state of the respective protein complex. This regulation is known as control by epistasy of synthesis (CES) and matches protein synthesis with the requirements of protein complex assembly in photosystem II (PSII), the cytochrome b6f complex (Cyt b6f), photosystem I (PSI), ATP synthase and Rubisco . In embryophytes, however, CES was only described to coordinate synthesis of the large and small subunits of Rubisco, raising the question if additional CES mechanisms exist in land plants or if stoichiometric photosynthetic protein accumulation is only achieved by the wasteful degradation of excess subunits. We systematically examined suitable tobacco and Arabidopsis mutants with assembly defects in PSII, PSI, Cyt b6f complex, ATP synthase, NDH (NAD(P)H dehydrogenase-like) complex and Rubisco for feedback regulation. Thereby, we validated the CES in Rubisco and uncovered translational feedback regulation in PSII, involving psbA, psbB, psbD and psbH and in Cyt b6f, connecting PetA and PetB protein synthesis. Remarkably, some of these feedback regulation mechanisms are not conserved between the green alga and embryophytes. Our data do not provide any evidence for CES in PSI, ATP synthase or NDH complex assembly in embryophytes. In addition, our data disclose translational feedback regulation adjusting PSI levels with PSII accumulation. Overall, we discovered commonalities and differences in assembly-dependent feedback regulation of photosynthetic complexes between embryophytes and green algae.
Project description:Prions are infectious proteins that can adopt a structural conformation different from that of the normal protein. This change of conformation is then propagated among other molecules of the same protein. Prions are associated with neurodegenerative diseases in mammals, but are also found in fungi (in the yeast Saccharomyces cerevisiae and the filamentous fungus Podospora anserina), in which they control heritable traits. They are widespread in wild yeast strains, suggesting a biologically important role. [PSI+] is one of the most widely studied yeast prions. It corresponds to an aggregated conformation of the translational release factor, eRF3, which suppresses nonsense codons. [PSI+] modifies cellular fitness, inducing various phenotypes, depending on the genetic background. However, the genes displaying [PSI+]-controlled expression remain largely unknown. We used the recently described ribosome profiling approach to identify genes displaying changes in expression in the presence of [PSI+]. This made it possible to determine the positions of all active ribosomes within the genome, in both [PSI+] and [PSI-] isogenic strains. Comparisons of the translatomes and transcriptomes of the two strains revealed that the primary effect of [PSI+] was to repress genes involved in the stress response. Thus, we provide the first description of the global translational effect of [PSI+] and a new genetic explanation of the phenotypic differences between [PSI-] and [PSI+] strains under stress conditions.
Project description:Here, we developed a Ψ RNA immunoprecipitation sequencing method (Ψ-RIP-seq) combined with direct RNA sequencing by Oxford Nanopore Technologies to detect mRNA Ψ transcriptome-wide. We identified a large number of novel Ψs in mRNA, revealing a conserved enrichment of Ψ in mRNA 3′ UTR. We further showed that a genome-wide association of Ψ with mRNA polyadenylation, and uncovered that cleavage factor complex I (CFI) regulated Ψ generation in mRNA 3′ UTR. We finally demonstrated that Ψ in mRNA 3′ UTR promoted mRNA stability in a CFI-dependent manner.