Going to extremes - a metagenomic journey into the dark matter of life

The Virus-X-Viral Metagenomics for Innovation Value-project was a scientific expedition to explore and exploit uncharted territory of genetic diversity in extreme natural environments such as geothermal hot springs and deep-sea ocean ecosystems. Specifically, the project was set to analyse and exploit viral metagenomes with the ultimate goal of developing new gene products with high innovation value for applications in biotechnology, pharmaceutical, medical, and the life science sectors. Viral gene pool analysis is also essential to obtain fundamental insight into ecosystem dynamics and to investigate how viruses influence the evolution of microbes and multicellular organisms. The Virus-X Consortium, established in 2016, included experts from eight European countries. The unique approach based on high throughput bioinformatics technologies combined with structural and functional studies resulted in the development of a biodiscovery pipeline of significant capacity and scale. The activities within the Virus-X consortium cover the entire range from bioprospecting and methods development in bioinformatics to protein production and characterisation, with the final goal of translating our results into new products for the bioeconomy. The significant impact the consortium made in all of these areas was possible due to the successful cooperation between expert teams that worked together to solve a complex scientific problem using state-of-the-art technologies as well as developing novel tools to explore the virosphere, widely considered as the last great frontier of life.

Cytokinin Response Factor 5 has transcriptional activity governed by its C-terminal domain

Cytokinin Response Factors (CRFs) are AP2/ERF transcription factors involved in cytokinin signal transduction. CRF proteins consist of a N-terminal dimerization domain (CRF domain), an AP2 DNA-binding domain, and a clade-specific C-terminal region of unknown function. Using a series of sequential deletions in yeast-2-hybrid assays, we provide evidence that the C-terminal region of Arabidopsis CRF5 can confer transactivation activity. Although comparative analyses identified evolutionarily conserved protein sequence within the C-terminal region, deletion experiments suggest that this transactivation domain has a partially redundant modular structure required for activation of target gene transcription.

Getting ready for host invasion: elevated expression and action of xyloglucan endotransglucosylases/hydrolases in developing haustoria of the holoparasitic angiosperm Cuscuta

Changes in cell walls have been previously observed in the mature infection organ, or haustorium, of the parasitic angiosperm Cuscuta, but are not equally well charted in young haustoria. In this study, we focused on the molecular processes in the early stages of developing haustoria; that is, before the parasite engages in a physiological contact with its host. We describe first the identification of differentially expressed genes in young haustoria whose development was induced by far-red light and tactile stimuli in the absence of a host plant by suppression subtractive hybridization. To improve sequence information and to aid in the identification of the obtained candidates, reference transcriptomes derived from two species of Cuscuta, C. gronovii and C. reflexa, were generated. Subsequent quantitative gene expression analysis with different tissues of C. reflexa revealed that among the genes that were up-regulated in young haustoria, two xyloglucan endotransglucosylase/hydrolase (XTH) genes were highly expressed almost exclusively at the onset of haustorium development. The same expression pattern was also found for the closest XTH homologues from C. gronovii. In situ assays for XTH-specific action suggested that xyloglucan endotransglucosylation was most pronounced in the cell walls of the swelling area of the haustorium facing the host plant, but was also detectable in later stages of haustoriogenesis. We propose that xyloglucan remodelling by Cuscuta XTHs prepares the parasite for host infection and possibly aids the invasive growth of the haustorium.

Cell wall composition profiling of parasitic giant dodder (Cuscuta reflexa) and its hosts: a priori differences and induced changes

Host plant penetration is the gateway to survival for holoparasitic Cuscuta and requires host cell wall degradation. Compositional differences of cell walls may explain why some hosts are amenable to such degradation while others can resist infection. Antibody-based techniques for comprehensive profiling of cell wall epitopes and cell wall-modifying enzymes were applied to several susceptible hosts and a resistant host of Cuscuta reflexa and to the parasite itself. Infected tissue of Pelargonium zonale contained high concentrations of de-esterified homogalacturonans in the cell walls, particularly adjacent to the parasite's haustoria. High pectinolytic activity in haustorial extracts and high expression levels of pectate lyase genes suggest that the parasite contributes directly to wall remodeling. Mannan and xylan concentrations were low in P. zonale and in five susceptible tomato introgression lines, but high in the resistant Solanum lycopersicum cv M82, and in C. reflexa itself. Knowledge of the composition of resistant host cell walls and the parasite's own cell walls is useful in developing strategies to prevent infection by parasitic plants.

Cell wall glycoproteins at interaction sites between parasitic giant dodder (Cuscuta reflexa) and its host Pelargonium zonale

The process of host plant penetration by parasitic dodder (genus Cuscuta) is accompanied by molecular and structural changes at the host/parasite interface. Recently, changes in pectin methyl esterification levels in the host cell walls abutting parasitic cells in established infection sites were reported. In addition to that, we show here that the composition of cell wall glycoproteins in Cuscuta-infected Pelargonium zonale undergoes substantial changes. While several arabinogalactan protein epitopes exhibit decreased abundances in the vicinity of the Cuscuta reflexa haustorium, extensins tend to increase in the infected areas.

Improving the accuracy of expression data analysis in time course experiments using resampling

Background

As time series experiments in higher eukaryotes usually obtain data from different individuals collected at the different time points, a time series sample itself is not equivalent to a true biological replicate but is, rather, a combination of several biological replicates. The analysis of expression data derived from a time series sample is therefore often performed with a low number of replicates due to budget limitations or limitations in sample availability. In addition, most algorithms developed to identify specific patterns in time series dataset do not consider biological variation in samples collected at the same conditions.

Results

Using artificial time course datasets, we show that resampling considerably improves the accuracy of transcripts identified as rhythmic. In particular, the number of false positives can be greatly reduced while at the same time the number of true positives can be maintained in the range of other methods currently used to determine rhythmically expressed genes.

Conclusions

The resampling approach described here therefore increases the accuracy of time series expression data analysis and furthermore emphasizes the importance of biological replicates in identifying oscillating genes. Resampling can be used for any time series expression dataset as long as the samples are acquired from independent individuals at each time point.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-014-0352-8) contains supplementary material, which is available to authorized users.