Dinoflagellate chromosomes represent a unique evolutionary experiment, as they exist in a permanently condensed, liquid crystalline state; are not packaged by histones; and contain genes organized into tandem gene arrays, with minimal transcriptional regulation. We analyze the three-dimensional genome of Breviolum minutum, and find large topological domains (dinoflagellate topologically associating domains, which we term 'dinoTADs') without chromatin loops, which are demarcated by convergent gene array boundaries. Transcriptional inhibition disrupts dinoTADs, implicating transcription-induced supercoiling as the primary topological force in dinoflagellates.

Bacteria and archaea have evolved defense and regulatory mechanisms to cope with various environmental stressors, including virus attack. This arsenal has been expanded by the recent discovery of the versatile CRISPR-Cas system, which has two novel features. First, the host can specifically incorporate short sequences from invading genetic elements (virus or plasmid) into a region of its genome that is distinguished by clustered regularly interspaced short palindromic repeats (CRISPRs). Second, when these sequences are transcribed and precisely processed into small RNAs, they guide a multifunctional protein complex (Gas proteins) to recognize and cleave incoming foreign genetic material. This adaptive immunity system, which uses a library of small noncoding RNAs as a potent weapon against fast-evolving viruses, is also used as a regulatory system by the host. Exciting breakthroughs in understanding the mechanisms of the CRISPR-Cas system and its potential for biotechnological applications and understanding evolutionary dynamics are discussed.

The photosystem I (PSI) complex consisting of reaction center (RC) subunits, several peripheral subunits and many co-factors, is present in the thylakoid membranes of chloroplasts and cyanobacteria. The assembly of RC subunits (PsaA/B) that bind electron transfer co-factors and antenna pigments is an intricate process, and is mediated by several auxiliary factors such as Ycf3, Y3IP1/CGL59, Ycf4 and Ycf37/PYG7/CGL71. However, their precise molecular mechanisms in RC assembly remain to be addressed. Here we purified four PSI auxiliary factors by affinity chromatography, and characterized co-purified PSI assembly intermediates. We suggest that Ycf3 assists the initial assembly of newly synthesized PsaA/B subunits into an RC subcomplex, while Y3IP1 may be involved in transferring the RC subcomplex from Ycf3 to the Ycf4 module that stabilizes it. CGL71 may form an oligomer that transiently interacts with the PSI RC subcomplex, physically protecting it under oxic conditions until association with the peripheral PSI subunits occurs. Together, our results reveal the interplay among four auxiliary factors required for the stepwise assembly of the PSI RC.

In recent years there has been growing appreciation of the unexpected genetic diversity of microbes in the environment. This diversity has important implications for our understanding of photosynthesis in populations and in the environment. Conventional methodologies often cannot effectively capture this aspect. This chapter describes new approaches including comparative genomic and metagenomic approaches combined with a more detailed understanding of the metabolism and functionalities of cyanobacteria. This approach, which can be defined broadly as "functional ecogenomics" is partly motivated by the availability of high-throughput sequence data, which are steadily being acquired. The focus is on unicellular cyanobacteria in the hot spring microbial mats of Yellowstone National Park, which are primary producers in this prokaryotic community. We took a three-pronged approach, in which we (a) acquired complete genome sequences from two dominant Synechococcus sp. and carried out a comparative genomic analysis to understand the functional differences between these temperature adapted isolates; (b) produced a metagenome dataset that allows us to place genomic information in the context of the community within which these cyanobacteria grow and evolve; and (c) obtained pure isolates of some dominant organisms that allow us to manipulate them in a well-defined laboratory setting. In situ transcriptomics has allowed quantification of transcripts during the diel cycle. These diverse approaches and the ability to measure environmental parameters such as light and O-2 levels allow us detailed insight into the microbial mat system. Such an approach could be used to study a wide array of photosynthetic microorganisms as populations and interacting communities. As sequencing capacity, single cell capture techniques, proteomics and imaging techniques become more widely accessible we expect to obtain ever more detailed information about natural communities.

The genomes of the two closely related freshwater thermophilic cyanobacteria Synechococcus sp. strain JA-3-3Ab and Synechococcus sp. strain JA-2-3B' a(2-13) each host several families of insertion sequences (ISSoc families) at various copy numbers, resulting in an overall high abundance of insertion sequences in the genomes. In addition to full-length copies, a large number of internal deletion variants have been identified. ISSoc2 has two variants (ISSoc2 partial derivative-1 and ISSoc2 partial derivative-2) that are observed to have multiple near-exact copies. Comparison of environmental metagenomic sequences to the Synechococcus genomes reveals novel placement of copies of ISSoc2, ISSoc2 partial derivative-1, and ISSoc2 partial derivative-2. Thus, ISSoc2 partial derivative-1 and ISSoc2 partial derivative-2 appear to be active nonautonomous mobile elements derived by internal deletion from ISSoc2. Insertion sites interrupting genes that are likely critical for cell viability were detected; however, most insertions either were intergenic or were within genes of unknown function. Most novel insertions detected in the metagenome were rare, suggesting a stringent selective environment. Evidence for mobility of internal deletion variants of other insertion sequences in these isolates suggests that this is a general mechanism for the formation of miniature insertion sequences.

Synechocystis sp., a common unicellular freshwater cyanobacterium, has been used as a model organism to study phototaxis, an ability to move in the direction of a light source. This microorganism displays a number of additional characteristics such as delayed motion, surface dependence, and a quasi-random motion, where cells move in a seemingly disordered fashion instead of in the direction of the light source, a global force on the system. These unexplained motions are thought to be modulated by local interactions between cells such as intercellular communication. In this paper, we consider only local interactions of these phototactic cells in order to mathematically model this quasi-random motion. We analyze an experimental data set to illustrate the presence of quasi-random motion and then derive a stochastic dynamic particle system modeling interacting phototactic cells. The simulations of our model are consistent with experimentally observed phototactic motion. (C) 2012 Elsevier Ltd. All rights reserved.

Phosphorus (P) assimilation and polyphosphate (polyP) synthesis were investigated in Chlamydomonas reinhardtii by supplying phosphate (PO43-; 10 mg P center dot L-1) to P-depleted cultures of wildtypes, mutants with defects in genes involved in the vacuolar transporter chaperone (VTC) complex, and VTC-complemented strains. Wildtype C. reinhardtii assimilated PO43- and stored polyP within minutes of adding PO43- to cultures that were P-deprived, demonstrating that these cells were metabolically primed to assimilate and store PO43-. In contrast, vtc1 and vtc4 mutant lines assayed under the same conditions never accumulated polyP, and PO43- assimilation was considerably decreased in comparison with the wildtypes. In addition, to confirm the bioinformatics inferences and previous experimental work that the VTC complex of C. reinhardtii has a polyP polymerase function, these results evidence the influence of polyP synthesis on PO43- assimilation in C. reinhardtii. RNA-sequencing was carried out on C. reinhardtii cells that were either P-depleted (control) or supplied with PO43- following P depletion (treatment) in order to identify changes in the levels of mRNAs correlated with the P status of the cells. This analysis showed that the levels of VTC1 and VTC4 transcripts were strongly reduced at 5 and 24 h after the addition of PO43- to the cells, although polyP granules were continuously synthesized during this 24 h period. These results suggest that the VTC complex remains active for at least 24 h after supplying the cells with PO43-. Further bioassays and sequence analyses suggest that inositol phosphates may control polyP synthesis via binding to the VTC SPX domain.