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Photosynthetic organisms provide food and energy for nearly all life on Earth, yet half of their protein-coding genes remain uncharacterized 1 , 2 . Characterization of these genes could be greatly accelerated by new genetic resources for unicellular organisms. Here we generated a genome-wide, indexed library of mapped insertion mutants for the unicellular alga Chlamydomonas reinhardtii . The 62,389 mutants in the library, covering 83% of nuclear protein-coding genes, are available to the community. Each mutant contains unique DNA barcodes, allowing the collection to be screened as a pool. We performed a genome-wide survey of genes required for photosynthesis, which identified 303 candidate genes. Characterization of one of these genes, the conserved predicted phosphatase-encoding gene CPL3 , showed that it is important for accumulation of multiple photosynthetic protein complexes. Notably, 21 of the 43 higher-confidence genes are novel, opening new opportunities for advances in understanding of this biogeochemically fundamental process. This library will accelerate the characterization of thousands of genes in algae, plants, and animals. Generation of a library of 62,389 mapped insertion mutants for the unicellular alga Chlamydomonas reinhardtii enables screening for genes required for photosynthesis and the identification of 303 candidate genes.

Most genes in photosynthetic organisms remain functionally uncharacterized. Here, using a barcoded mutant library of the model eukaryotic alga Chlamydomonas reinhardtii , we determined the phenotypes of more than 58,000 mutants under more than 121 different environmental growth conditions and chemical treatments. A total of 59% of genes are represented by at least one mutant that showed a phenotype, providing clues to the functions of thousands of genes. Mutant phenotypic profiles place uncharacterized genes into functional pathways such as DNA repair, photosynthesis, the CO 2 -concentrating mechanism and ciliogenesis. We illustrate the value of this resource by validating phenotypes and gene functions, including three new components of an actin cytoskeleton defense pathway. The data also inform phenotype discovery in land plants; mutants in Arabidopsis thaliana genes exhibit phenotypes similar to those we observed in their Chlamydomonas homologs. We anticipate that this resource will guide the functional characterization of genes across the tree of life. Systematic phenotyping of 58,101 mutants of the model eukaryotic alga Chlamydomonas reinhardtii under 121 environmental and chemical stress conditions provides a large resource for characterizing gene function.

Plastid protein homeostasis is critical during chloroplast biogenesis and responses to changes in environmental conditions. Proteases and molecular chaperones involved in plastid protein quality control are encoded by the nucleus except for the catalytic subunit of ClpP, an evolutionarily conserved serine protease. Unlike its Escherichia coli ortholog, this chloroplast protease is essential for cell viability. To study its function, we used a recently developed system of repressible chloroplast gene expression in the alga Chlamydomonas reinhardtii. Using this repressible system, we have shown that a selective gradual depletion of ClpP leads to alteration of chloroplast morphology, causes formation of vesicles, and induces extensive cytoplasmic vacuolization that is reminiscent of autophagy. Analysis of the transcriptome and proteome during ClpP depletion revealed a set of proteins that are more abundant at the protein level, but not at the RNA level. These proteins may comprise some of the ClpP substrates. Moreover, the specific increase in accumulation, both at the RNA and protein level, of small heat shock proteins, chaperones, proteases, and proteins involved in thylakoid maintenance upon perturbation of plastid protein homeostasis suggests the existence of a chloroplast-to-nucleus signaling pathway involved in organelle quality control. We suggest that this represents a chloroplast unfolded protein response that is conceptually similar to that observed in the endoplasmic reticulum and in mitochondria.

In response to proteotoxic stress, chloroplasts communicate with the nuclear gene expression system through a chloroplast unfolded protein response (cpUPR). We isolated Chlamydomonas reinhardtii mutants that disrupt cpUPR signaling and identified a gene encoding a previously uncharacterized cytoplasmic protein kinase, termed Mars1—for m utant a ffected in chloroplast-to-nucleus r etrograde s ignaling—as the first known component in cpUPR signal transmission. Lack of cpUPR induction in MARS1 mutant cells impaired their ability to cope with chloroplast stress, including exposure to excessive light. Conversely, transgenic activation of cpUPR signaling conferred an advantage to cells undergoing photooxidative stress. Our results indicate that the cpUPR mitigates chloroplast photodamage and that manipulation of this pathway is a potential avenue for engineering photosynthetic organisms with increased tolerance to chloroplast stress. Life on Earth crucially depends on photosynthesis, the process by which energy stored in sunlight is harnessed to convert carbon dioxide into sugars and oxygen. In plants and algae, photosynthesis occurs in specialized cellular compartments called chloroplasts. Inside chloroplasts, complex molecular machines absorb light and channel its energy into the appropriate chemical reactions. These machines are composed of proteins that need to be assembled and maintained. However, proteins can become damaged, and when this occurs, they must be recognized, removed, and replaced. When exposed to bright light, the photosynthetic machinery is pushed into overdrive and protein damage is accelerated. In response, the chloroplast sends an alarm signal to activate a protective system called the “chloroplast unfolded protein response”, or cpUPR for short. The cpUPR leads to the production of specialized proteins that help protect and repair the chloroplast. It was not known how plants and algae evaluate the level of damaged proteins in the chloroplast, or which signals trigger the cpUPR. To address these questions, Perlaza et al. designed a method to identify the molecular components of the alarm signal. These experiments used specially engineered cells from the algae Chlamydomonas reinhardtii that fluoresced when the cpUPR was activated. Perlaza et al. mutagenized these cells – that is, damaged the cells’ DNA to cause random changes in the genetic code. If a mutagenized cell no longer fluoresced in response to protein damage, it indicated that communication between protein damage and the cpUPR had been broken. In other words, the mutation had damaged a piece of DNA that encoded a protein critical for activating the cpUPR. These experiments identified one protein – which Perlaza et al. named Mars1 – as a crucial molecular player that is required to trigger the cpUPR. Algal cells with defective Mars1 were more vulnerable to chloroplast damage, including that caused by excessive light. These discoveries in algae will serve as a foundation for understanding the mechanism and significance of the cpUPR in land plants. Perlaza et al. also found that mild artificial activation of the cpUPR could preemptively guard cells against damaged chloroplast proteins. This suggests that the cpUPR could be harnessed in agriculture, for example, to help crop plants endure harsher climates.

The many centuries of Argentinian archaeology have been studied by a number of scholars (e.g. Fern´andez 1982;Crivelli 1990; Politis 1995, 2003, 2007; Nastri 1999, 2004; Ramundo 2007a, 2008a, 2008c; Borrazzo et al. 2009). Although the analysis of current topics in the discipline and a tentative view on its future will be the aim of this critical appraisal, it does not pretend to be exhaustive, but the starting point for enriching the discussion. Amongst the topics briefly addressed are the plurality of theoretical frameworks, the variety of areas of specialisation, the protection of archaeological heritage, ethical aspects of the discipline, an analysis of academic training and the relationship between archaeology and local and/or aboriginal communities.

Although reverse genetics has been used to elucidate the function of numerous chloroplast proteins, the characterization of essential plastid genes and their role in chloroplast biogenesis and cell survival has not yet been achieved. Therefore, we developed a robust repressible chloroplast gene expression system in the unicellular alga Chlamydomonas reinhardtii based mainly on a vitamin-repressible riboswitch, and we used this system to study the role of two essential chloroplast genes: ribosomal protein S12 (rps12), encoding a plastid ribosomal protein, and rpoA, encoding the α-subunit of chloroplast bacterial-like RNA polymerase. Repression of either of these two genes leads to the arrest of cell growth, and it induces a response that involves changes in expression of nuclear genes implicated in chloroplast biogenesis, protein turnover, and stress. This response also leads to the overaccumulation of several plastid transcripts and reveals the existence of multiple negative regulatory feedback loops in the chloroplast gene circuitry.

In photosynthetic eukaryotes, thousands of proteins are translated in the cytosol and imported into the chloroplast through the concerted action of two translocons—termed TOC and TIC—located in the outer and inner membranes of the chloroplast envelope, respectively. The degree to which the molecular composition of the TOC and TIC complexes is conserved over phylogenetic distances has remained controversial. Here, we combine transcriptomic, biochemical, and genetic tools in the green alga Chlamydomonas (Chlamydomonas reinhardtii) to demonstrate that, despite a lack of evident sequence conservation for some of its components, the algal TIC complex mirrors the molecular composition of a TIC complex from Arabidopsis thaliana. The Chlamydomonas TIC complex contains three nuclear-encoded subunits, Tic20, Tic56, and Tic100, and one chloroplast-encoded subunit, Tic214, and interacts with the TOC complex, as well as with several uncharacterized proteins to form a stable supercomplex (TIC-TOC), indicating that protein import across both envelope membranes is mechanistically coupled. Expression of the nuclear and chloroplast genes encoding both known and uncharacterized TIC-TOC components is highly coordinated, suggesting that a mechanism for regulating its biogenesis across compartmental boundaries must exist. Conditional repression of Tic214, the only chloroplast-encoded subunit in the TIC-TOC complex, impairs the import of chloroplast proteins with essential roles in chloroplast ribosome biogenesis and protein folding and induces a pleiotropic stress response, including several proteins involved in the chloroplast unfolded protein response. These findings underscore the functional importance of the TIC-TOC supercomplex in maintaining chloroplast proteostasis.

Here, we provide a summary of the 2017 Gordon Research Conference on Photosynthesis: “Photosynthetic plasticity: from the environment to synthetic systems”. This conference was held at the Grand Summit Resort Hotel at Sunday River, Newry, Maine, USA, from July 16 to 21, 2017. We have also included here a brief description of the Gordon Research Seminar (for students and post-docs) held during 2 days preceding this conference. Following the conclusion of the conference’s scientific program, four young scientists (Han Bao, Vivek Tiwari, Setsuko Wakao, and Usha Lingappa) were recognized for their research presentations, each of whom received a book as a gift from one of us (Govindjee). Having chaired the 2015 Gordon Research Conference on Photosynthesis in 2015, Fabrice Rappaport, who lost his fight against cancer in January 2016, was remembered for his profound impact on the field of photosynthesis research.

Plastid protein homeostasis is critical during chloroplast biogenesis and responses to changes in environmental conditions. Proteases and molecular chaperones involved in plastid protein quality control are encoded by the nucleus except for the catalytic subunit of CIpP, an evolutionarily conserved serine protease. Unlike its Escherichia coli ortholog, this chloroplast protease is essential for cell viability. To study its function, we used a recently developed system of repressible chloroplast gene expression in the alga Chlamydomonas reinhardtii. Using this repressible system, we have shown that a selective gradual depletion of CIpP leads to alteration of chloroplast morphology, causes formation of vesicles, and induces extensive cytoplasmic vacuolization that is reminiscent of autophagy. Analysis of the transcriptome and proteome during CIpP depletion revealed a set of proteins that are more abundant at the protein level, but not at the RNA level. These proteins may comprise some of the CIpP substrates. Moreover, the specific increase in accumulation, both at the RNA and protein level, of small heat shock proteins, chaperones, proteases, and proteins involved in thylakoid maintenance upon perturbation of plastid protein homeostasis suggests the existence of a chloroplast-to-nucleus signaling pathway involved in organelle quality control. We suggest that this represents a chloroplast unfolded protein response that is conceptually similar to that observed in the endoplasmic reticulum and in mitochondria.

Additionally, a colonial post operated in the locality of La Cueva, with its use extending at least until the time of the Independence Wars. In the 18th century, La Cueva became an attractive hub for settlers from both nearby and distant places who either established themselves in the village of the same name or frequented its church (Nuestra Senora de la Concepcion) for baptisms, marriages, and it was also the chosen place for burials of different social actors, possibly because it served as an economic center for the region. All the archaeological and documentary evidence, studied with the goal of analyzing and comparing the existence of mobility or circulation within and beyond the quebrada, demonstrates the connection of this quebrada with the Jujena Puna, Yungas, other sectors of the Quebrada de Humahuaca, and neighboring countries like Chile, Bolivia, and Peru. Keywords: interaction, pre-hispanic, post-Hispanic, Quebrada de La Cueva, Northwestern Argentina MOVILIDAD EN TIEMPOS PREHISPÁNICOS Y POST-HISPÁNICOS... Esto se debe a la riqueza agrícola que hay en sus sectores inferior y medio -evidenciada desde la arqueología (Ramundo, 2022a)-, y a la existencia de excelentes vegas de altura en su sector superior, que habrían permitido la caza-recolección en etapas tempranas, y el desarrollo de actividades pastoriles desde la domesticación de los animales hasta el presente, dado que el pastoreo de camélidos es uno de los principales medios de subsistencia de su población actual. Pero además, consideramos que este mismo paisaje también ha sido escenario de una incesante y fuctuante movilidad de personas, objetos e ideas a lo largo de su extensa ocupación (desde el Período Formativo hasta la actualidad), posiblemente motivada por el atractivo que la zona brinda, y por la excelente conexión que otorga con otros sectores dentro y fuera del Noroeste Argentino.