Project description:Photoacclimation of unicellular algae allows for reversible changes in the number and/or effective absorption cross section of photosynthetic units on time scales of hours to days in response to changes in irradiance. The process involves an enigmatic signaling pathway from the plastid to the nucleus.Our results reveal, for the first time, a fundamental pathway of retrograde signal transduction in a eukaryotic photosynthetic alga.
Project description:Bigelowiella natans is a marine chlorarachniophyte whose plastid was acquired secondarily via endosymbiosis with a green alga. Integrating a photosynthetic endosymbiont within the host metabolism on route to plastid evolution would require the acquisition of strategies for coping with changes in light intensity and modifications of host genes to appropriately respond to changes in photosynthetic metabolism. To investigate the transcriptional response to light intensity in chlorarachniophytes, we conducted an RNA-seq experiment to identify differentially-expressed genes following four-hour shift to high or very-low light. A shift to high light altered the expression of over 2000 genes, many involved with photosynthesis, primary metabolism, and reactive-oxygen scavenging. These changes are related to an attempt to optimize photosynthesis and increase energy sinks for excess reductant, while minimizing photo-oxidative stress. A transfer to very-low light resulted in a lower photosynthetic performance and metabolic alteration, reflecting an energy-limited state. Genes located on the nucleomorph, the vestigial nucleus in the plastid, had few changes in expression in either light treatment, indicating this organelle has relinquished most transcriptional control to the nucleus. Overall, during plastid origin, both host and transferred endosymbiont genes evolved a harmonized transcriptional network to respond to a classic photosynthetic stress.
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:Responses of photosynthetic organisms to sulfur starvation include (i) increasing the capacity of the cell for transporting and/or assimilating exogenous sulfate, (ii) restructuring cellular features to conserve sulfur resources, and (iii) modulating metabolic processes and rates of cell growth and division. We used microarray analyses to obtain a genome-level view of changes in mRNA abundances in the green alga Chlamydomonas reinhardtii during sulfur starvation. The work confirms and extends upon previous findings showing that sulfur deprivation elicits changes in levels of transcripts for proteins that help scavenge sulfate and economize on the use of sulfur resources. Changes in levels of transcripts encoding members of the light-harvesting polypeptide family, such as LhcSR2, suggest restructuring of the photosynthetic apparatus during sulfur deprivation. There are also significant changes in levels of transcripts encoding enzymes involved in metabolic processes (e.g., carbon metabolism), intracellular proteolysis, and the amelioration of oxidative damage; a marked and sustained increase in mRNAs for a putative vanadium chloroperoxidase and a peroxiredoxin may help prolong survival of C. reinhardtii during sulfur deprivation. Furthermore, many of the sulfur stress-regulated transcripts (encoding polypeptides associated with sulfate uptake and assimilation, oxidative stress, and photosynthetic function) are not properly regulated in the sac1 mutant of C. reinhardtii, a strain that dies much more rapidly than parental cells during sulfur deprivation. Interestingly, sulfur stress elicits dramatic changes in levels of transcripts encoding putative chloroplast-localized chaperones in the sac1 mutant but not in the parental strain. These results suggest various strategies used by photosynthetic organisms during acclimation to nutrient-limited growth.
Project description:Responses of photosynthetic organisms to sulfur starvation include (i) increasing the capacity of the cell for transporting and/or assimilating exogenous sulfate, (ii) restructuring cellular features to conserve sulfur resources, and (iii) modulating metabolic processes and rates of cell growth and division. We used microarray analyses to obtain a genome-level view of changes in mRNA abundances in the green alga Chlamydomonas reinhardtii during sulfur starvation. The work confirms and extends upon previous findings showing that sulfur deprivation elicits changes in levels of transcripts for proteins that help scavenge sulfate and economize on the use of sulfur resources. Changes in levels of transcripts encoding members of the light-harvesting polypeptide family, such as LhcSR2, suggest restructuring of the photosynthetic apparatus during sulfur deprivation. There are also significant changes in levels of transcripts encoding enzymes involved in metabolic processes (e.g., carbon metabolism), intracellular proteolysis, and the amelioration of oxidative damage; a marked and sustained increase in mRNAs for a putative vanadium chloroperoxidase and a peroxiredoxin may help prolong survival of C. reinhardtii during sulfur deprivation. Furthermore, many of the sulfur stress-regulated transcripts (encoding polypeptides associated with sulfate uptake and assimilation, oxidative stress, and photosynthetic function) are not properly regulated in the sac1 mutant of C. reinhardtii, a strain that dies much more rapidly than parental cells during sulfur deprivation. Interestingly, sulfur stress elicits dramatic changes in levels of transcripts encoding putative chloroplast-localized chaperones in the sac1 mutant but not in the parental strain. These results suggest various strategies used by photosynthetic organisms during acclimation to nutrient-limited growth. An all pairs experiment design type is where all labeled extracts are compared to every other labeled extract. Computed
Project description:Different intensities of high temperatures affect the growth of photosynthetic cells in nature. To elucidate the underlying mechanisms, we cultivated the unicellular green alga Chlamydomonas reinhardtii under highly controlled photobioreactor conditions and revealed systems-wide shared and unique responses to 24-hour moderate (35oC) and acute (40oC) high temperatures and subsequent recovery at 25oC. We identified transcripts/proteins with unique differential regulation at 35oC, uncovering previously overlooked novel elements in response to moderate high temperature. Heat at 35oC increased transcripts/proteins involved in gluconeogensis/glyoxylate-cycle for carbon uptake, promoted growth, and increased starch accumulation. Heat at 40oC inhibited growth, resulting in carbon uptake over usage and increased starch accumulation. Heat at 35oC transiently arrested the cell cycle followed by partial synchronization while 40oC inhibited DNA replication and arrested the cell cycle. Both high temperatures induced photoprotection, while 40oC decreased photosynthetic efficiencies, distorted thylakoid/pyrenoid ultrastructure, and affected the carbon concentrating mechanism. We demonstrated increased transcript/protein correlation during heat, which decreased during recovery, suggesting reduced post-transcriptional regulation during heat may help coordinate heat tolerance activities efficiently. During recovery after both treatments, transcripts/proteins related to DNA synthesis increased while those involved in photosynthetic light reactions decreased. We propose down-regulating photosynthetic light reactions during DNA replication benefits cell cycle resumption by reducing ROS production. Our results provide potential targets to increase thermotolerance in algae and crops.