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:Animal-algal photosymbioses are a unique group of symbiotic relationships in which animals harbor photosynthetic algae within their cells and tissues. Both marine and freshwater sponges host algal endosymbionts. In previous work, we demonstrated that freshwater sponges can acquire these endosymbionts horizontally through algal infection and that potentially conserved evolutionary pathways may lead to the establishment of the endosymbioses including those involved in endocytosis, ion transport, vesicle-mediated transport, innate immunity, redox regulation, and metabolic processes. Here, we show that algal symbionts can be transferred vertically from algal-bearing overwintering gemmules to adult sponges, and that their proliferation is enhanced by light. Sponges grown under light conditions harbored higher algal loads than those in the dark; however, algae were still able to proliferate and persist in sponges reared in the dark, occupying similar spatial locations to those grown in light. RNA-Seq analysis of algal-bearing sponges across developmental stages in light and dark conditions revealed genetic regulatory pathways involved in the transmission and establishment of the endosymbiosis. Differential expression analysis indicated that the endocytosis and SNARE pathways regulate the internalization and transport of algae at the earliest stage of hatching under light conditions and later in development under dark conditions, potentially contributing to the recruitment of endosymbiotic algae. In sponges hatched in the dark, genes involved in vesicle acidification are regulated, alongside changes in the expression of genes in the pentose phosphate pathway - a key metabolic route involved in redox homeostasis and circadian rhythm regulation via NADPH metabolism, is observed. E. muelleri serves as a versatile model system, supported by robust genomic and transcriptomic resources, for studying host-symbiont interactions. It offers a unique opportunity to investigate the molecular signaling and environmental factors that shape symbiosis in a system where the host can exist with or without algal endosymbionts, symbionts can be acquired either horizontally or vertically, and proliferation of the algae can occur with or without photosynthesis.
Project description:For the model alga Chlamydomonas, acclimation to diurnal low light (LL) or high light (HL) results in changes in photosynthetic complexes, chlorophyll content, thylakoid membrane architecture, and nonphotochemical quenching capacity that are maintained through the intervening night phases. To determine how diurnal photoacclimation influences algal fitness and document the molecular events during reacclimation upon a change in daylight intensity, we transitioned LL-acclimated populations to diurnal HL and HL-acclimated populations to diurnal LL and performed an RNA-Seq timecourse over two diurnal periods.
Project description:Different high temperatures adversely affect crop and algal yields with various responses in photosynthetic cells. The list of genes required for thermotolerance remains elusive. Additionally, it is unclear how carbon source availability affects heat responses in plants and algae. We utilized the insertional, indexed, genome-saturating mutant library of the unicellular, eukaryotic green alga Chlamydomonas reinhardtii to perform genome-wide, quantitative, pooled screens under moderate (35oC) or acute (40oC) high temperatures with or without organic carbon sources. We identified heat-sensitive mutants based on quantitative growth rates and identified putative heat tolerance genes (HTGs). By triangulating HTGs with heat-induced transcripts or proteins in wildtype cultures and MapMan functional annotations, we present a high/medium-confidence list of 933 Chlamydomonas genes with putative roles in heat tolerance. Triangulated HTGs include those with known thermotolerance roles and novel genes with little or no functional annotation. About 50% of these high-confidence HTGs in Chlamydomonas have orthologs in green lineage organisms, including crop species. Arabidopsis thaliana mutants deficient in the ortholog of a high-confidence Chlamydomonas HTG were also heat sensitive. This work expands our knowledge of heat responses in photosynthetic cells and provides engineering targets to improve thermotolerance in algae and crops.
Project description:Ultra-violet (UV) and high-intensity visible (VIS) radiation are environmental stressors known to harm photosynthetic organisms through the generation of reactive intermediates that damage photosynthetic machinery. This study shows the potential of using a thermoacidophilic red alga of the order Cyanidiales to model in situ algal gene expression dynamics as a function of UV exposure and seasonal shifts in UV-VIS intensity. These algae exhibit a dynamic seasonal biomass fluctuation referred to as 'mat decline' where viability drastically decreases as seasonal UV-VIS irradiance intensity increases. In Yellowstone National Park (YNP), temporal experiments coupling UV irradiance manipulations (filtering) with whole-community transcription profiling revealed significant cyanidial gene expression changes occurring as a result of exposure to UV, and that patterns of response adjust across low and high irradiance time periods. Separate analyses examined genes responding to either increasing seasonal UV or VIS intensity, or by the combined effects of both irradiance wavelengths (UV and VIS). Results not only corroborated known physiological changes to solar irradiance, but also suggested the strategies employed to deal with excess VIS and UV intensity may be highly integrated. Finally, a suite of comparative analyses determined the relative utility of environmental transcriptomics technologies in studying ecologically-relevant expression patterns. Results suggest in situ expression profiles will improve understanding of how photosynthetic organisms are responding to environmental stressors as they are observed in nature. 16 samples with 3 biological replicates each.