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:Photosystem I (PSI) enables photo-electron transfer and regulates photosynthesis in the bioenergetic membranes of cyanobacteria and chloroplasts. Being a multi-subunit complex, its macromolecular organization affects the dynamics of photosynthetic membranes. Here we reveal a chloroplast PSI from the green alga Chlamydomonas reinhardtii that is organized as a homodimer.
Project description:Photosystem I (PSI) enables photo-electron transfer and regulates photosynthesis in the bioenergetic membranes of cyanobacteria and chloroplasts. Being a multi-subunit complex, its macromolecular organization affects the dynamics of photosynthetic membranes. Here we reveal a chloroplast PSI from the green alga Chlamydomonas reinhardtii that is organized as a homodimer.
Project description:Antisense RNAs (asRNAs) have diverse functions across three superkingdoms of life. However, their physiological roles for photosynthesis, the most efficient conversion system of solar energy and carbon dioxide into desirable biofuel, are elusive. To understand asRNA-mediated photosynthetic response, we systematically identified non-coding asRNAs and analyzed their differential regulation upon high light and/or low temperature. We found that large fractions of antisense regions are pervasively transcribed and differentially induced upon the change of light and/or temperature. Particularly, photosynthesis and ribosome related genes are mostly regulated by asRNA. Futhermore, we found that 93 long non-coding asRNAs spanning more than half of the cognate open reading frames (ORFs), unexpectedly. Intriguingly, many of them are associated with photosynthetic genes and they have positive role to the expression level of their cognate ORFs. Thus, our systematic transcriptome analysis of photosynthetic response indicates that asRNAs may finetune transcriptional response to enable efficient photosynthetic energy conversion.
Project description:Unicellular cyanobacteria that do not fix nitrogen can survive prolonged periods of nitrogen starvation as bleached cells in a non-growing, dormant state. Upon re-addition of a usable nitrogen source, bleached cultures re-green within 48 hours and the cells return to vegetative growth. Here we investigated the process of resuscitation at the physiological and molecular level. Almost immediately upon nitrate addition, the cells initiate an amazingly organized resuscitation program: they first turn on respiration, gaining energy and activating the genes of the entire translational apparatus, genes for ATP synthesis and nitrate assimilation. Only after about 12 hours, the cells rebuild the photosynthetic apparatus and switch on photosynthesis. Analysis of the transcriptome in recovering cells shows a perfect match to the physiological processes and reveals a paramount dynamics of non-coding RNAs in awaking cells. This genetically encoded program ensures rapid colonization of habitats, in which nitrogen starvation imposes a recurring growth limitation.