The green yeast uses its plant-like clock to regulate its animal-like tail

Predetermined clockwork microbial worlds: Current understanding of aquatic microbial diel response from model systems to complex environments

In the photic zone of aquatic ecosystems, microorganisms with different metabolisms and their viruses form complex interactions and food webs. Within these interactions, phototrophic microorganisms such as eukaryotic microalgae and cyanobacteria interact directly with sunlight, and thereby generate circadian rhythms. Diel cycling originally generated in microbial phototrophs is directly transmitted toward heterotrophic microorganisms utilizing the photosynthetic products as they are excreted or exuded. Such diel cycling seems to be indirectly propagated toward heterotrophs as a result of complex biotic interactions. For example, cell death of phototrophic microorganisms induced by viral lysis and protistan grazing provides additional resources of dissolved organic matter to the microbial community, and so generates diel cycling in other heterotrophs with different nutrient dependencies. Likewise, differences in the diel transmitting pathway via complex interactions among heterotrophs, and between heterotrophs and their viruses, may also generate higher variation and time lag diel rhythms in different heterotrophic taxa. Thus, sunlight and photosynthesis not only contribute energy and carbon supply, but also directly or indirectly control diel cycling of the microbial community through complex interactions in the photic zone of aquatic ecosystems.

Genome-wide survey and expression analysis of Chlamydomonas reinhardtii U-box E3 ubiquitin ligases (CrPUBs) reveal a functional lipid metabolism module

E3 ubiquitin ligases determine the substrate specificity of ubiquitination. Plant U-box (PUB) E3 ligases, with a typical 70-amino acid U-box domain, participate in plant developmental processes and environmental responses. Thus far, 64 PUB proteins have been identified in Arabidopsis and 77 PUB proteins have been identified in Oryza. However, detailed studies on U-box genes in the model microalgae Chlamydomonas reinhardtii are lacking. Here, we present a comprehensive analysis of the genes encoding U-box family proteins in C. reinhardtii. Following BLASTP analysis, 30 full-length U-box genes were identified in the C. reinhardtii genome sequence. Bioinformatics analyses of CrPUB genes were performed to characterize the phylogenetic relationships, chromosomal locations and gene structures of each member. The 30 identified CrPUB proteins are clustered into 3 distinct subfamilies, and the genes for these proteins are unevenly distributed among 14 chromosomes. Furthermore, the quantitative real-time RT-PCR or semi-quantitative RT-PCR analysis of 30 CrPUB mRNA abundances under nitrogen starvation showed that 18 CrPUB genes were induced by N starvation and that 7 genes were repressed in the N-poor environment. We selected five CrPUB genes exhibiting marked changes in expression under N-free conditions for further analysis in RNAi experiments and examined the oil content of these gene-silenced transgenic strains. The silencing of CrPUB5 and CrPUB14, which are typically down-regulated under N starvation, induced 9.8%-45.0% and 14.4%-61.8% lipid accumulation, respectively. In contrast, the silencing of CrPUB11, CrPUB23 and CrPUB28, which are markedly up-regulated under N-free conditions, decreased the lipid content by 5.5%-27.8%, 8.1%-27.3% and 6.6%-27.9%, respectively. These results provide a useful reference for the identification and functional analysis of this gene family and fundamental information for microalgae lipid metabolism research.

Clocks in algae

As major contributors to global oxygen levels and producers of fatty acids, carotenoids, sterols, and phycocolloids, algae have significant ecological and commercial roles. Early algal models have contributed much to our understanding of circadian clocks at physiological and biochemical levels. The genetic and molecular approaches that identified clock components in other taxa have not been as widely applied to algae. We review results from seven species: the chlorophytes Chlamydomonas reinhardtii, Ostreococcus tauri, and Acetabularia spp.; the dinoflagellates Lingulodinium polyedrum and Symbiodinium spp.; the euglenozoa Euglena gracilis; and the red alga Cyanidioschyzon merolae. The relative simplicity, experimental tractability, and ecological and evolutionary diversity of algal systems may now make them particularly useful in integrating quantitative data from "omic" technologies (e.g., genomics, transcriptomics, metabolomics, and proteomics) with computational and mathematical methods.

Both subunits of the circadian RNA-binding protein CHLAMY1 can integrate temperature information

The circadian RNA-binding protein CHLAMY1 from the green alga Chlamydomonas reinhardtii consists of two subunits named C1 and C3. Changes in the C1 level cause arrhythmicity of the phototaxis rhythm, while alterations in the level of C3 lead to acrophase shifts. Thus, CHLAMY1 is involved in maintaining period and phase of the circadian clock. Here, we analyzed the roles of the two subunits in the integration of temperature information, the basis for other key properties of circadian clocks, including entrainment by temperature cycles and temperature compensation. Applied temperatures (18 degrees C and 28 degrees C) were in the physiological range of C. reinhardtii. While C1 is hyperphosphorylated at low temperature, the C3 expression level is up-regulated at 18 degrees C. An inhibitor experiment showed that this up-regulation occurs at the transcriptional level. Promoter analysis studies along with single promoter element mutations revealed that individual replacement of two DREB1A-boxes lowered the amplitude of c3 up-regulation at 18 degrees C, while replacement of an E-box abolished it completely. Replacement of the E-box also caused arrhythmicity of circadian-controlled c3 expression. Thus, the E-box has a dual function for temperature-dependent up-regulation of c3 as well as for its circadian expression. We also found that the temperature-dependent regulation of C1 and C3 as well as temperature entrainment are altered in the clock mutant per1, indicating that a temperature-controlled network of C1, C3, and PER1 exists.