Early Response to Dehydration Six-Like Transporter Family: Early Origin in Streptophytes and Evolution in Land Plants

Carbon management by plants involves the activity of many sugar transporters, which play roles in sugar subcellular partitioning and reallocation at the whole organism scale. Among these transporters, the early response to dehydration six-like (ESL) monosaccharide transporters (MSTs) are still poorly characterized although they represent one of the largest sugar transporter subfamilies. In this study, we used an evolutionary genomic approach to infer the evolutionary history of this multigenic family. No ESL could be identified in the genomes of rhodophytes, chlorophytes, and the brown algae Ectocarpus siliculosus, whereas one ESL was identified in the genome of Klebsormidium nitens providing evidence for the early emergence of these transporters in Streptophytes. A phylogenetic analysis using the 519 putative ESL proteins identified in the genomes of 47 Embryophyta species and being representative of the plant kingdom has revealed that ESL protein sequences can be divided into three major groups. The first and second groups originated in the common ancestor of all spermaphytes [ζ: 340 million years ago (MYA)] and of angiosperms (ε: 170–235 MYA), respectively, and the third group originated before the divergence of rosids and asterids (γ/1R: 117 MYA). In some eudicots (Vitales, Malpighiales, Myrtales, Sapindales, Brassicales, Malvales, and Solanales), the ESL family presents remarkable expansions of gene copies associated with tandem duplications. The analysis of non-synonymous and synonymous substitutions for the dN/dS ratio of the ESL copies of the genus Arabidopsis has revealed that ESL genes are evolved under a purifying selection even though the progressive increase of dN/dS ratios in the three groups suggests subdiversification phenomena. To further explore the possible acquisition of novel functions by ESL MSTs, we identified the gene structure and promoter cis-acting elements for Arabidopsis thaliana ESL genes. The expression profiling of Arabidopsis ESL unraveled some gene copies that are almost constitutively expressed, whereas other gene copies display organ-preferential expression patterns. This study provides an evolving framework to better understand the roles of ESL transporters in plant development and response to environmental constraints.

Spatial-temporal changes of macrophytobenthos in the coastal zone of the Reserve “Karan’sky” (Sevastopol City, Black Sea)

For the first time, a comparative analysis of the specific diversity, changes in the biomass of macrophytobenthos in the reserve “Karan’sky” coastal zone from 1964 to 2016 was performed on the basis of a landscape approach. A landscape map of the underwater coastal slope has been drawn up, three bottom natural complexes (BNC) have been identified. The BNC of psephite deposits dominated by C. crinita and Tr. barbata (up to 89.7–78.6% of the total biomass of macrophytes) is the main one. This complex is characterized by high floristic diversity and maximum values of the biomass of macrophytobenthos. The BNC of psephite deposits with C. crinita and Tr. barbata to predominate and with pebble-gravel deposits with broken shells alternate, where Ph. crispa is the dominant species, is characterized by high floristic diversity and a decreased proportion of C. crinite and Tr. barbata, the contribution of Ph. crispa to the total biomass of macrophytes is 14.4%. The BNC of psammitic deposits with Ph. crispa to predominate and with separately randomly located blocks, where Nereia filiformis and Zanardinia typus predominate, is characterized by low floristic diversity, the predominance of Phyllophora crispa (74.3% of the total biomass of macrophytes), and the preservation of perennial species. For more than 50 years, there was a reorganization and degradation of the plant component in all BNC (depth 0.5–10 m), which was probably due to the intensification of anthropogenic activity in the coastal zone. Eudesme virescens, Dictyota dichotoma, Feldmania irrgularis, Dasya baillouviana and Rhodochorton purpureum, which live in clean, open areas of the coast, have disappeared from the bottom vegetation, and macrophytes (Cladophora laetevirens, Ectocarpus siliculosus and C. virgatum), typical for eutrophic waters, have appeared in the duodenum. The biomass of epiphytes has increased (from 0.1 to 42.6% of the total biomass of macrophytes), and the role of dominant species has decreased: C. crinita, Tr. barbata (from 99.9 to 78.6%) and Ph. crispa (from 52.9 to 14.4% of the total biomass of macrophytes). The organization of the “Karan’sky” Reserve contributed to the preservation and partial restoration of the unique natural complex of marine flora and bottom vegetation, which is confirmed by the increased floristic diversity of algaeindicators of clean waters and the increased proportion of the Red Data Book species.

Genome–Scale Metabolic Networks Shed Light on the Carotenoid Biosynthesis Pathway in the Brown Algae Saccharina japonica and Cladosiphon okamuranus

Understanding growth mechanisms in brown algae is a current scientific and economic challenge that can benefit from the modeling of their metabolic networks. The sequencing of the genomes of Saccharina japonica and Cladosiphon okamuranus has provided the necessary data for the reconstruction of Genome–Scale Metabolic Networks (GSMNs). The same in silico method deployed for the GSMN reconstruction of Ectocarpus siliculosus to investigate the metabolic capabilities of these two algae, was used. Integrating metabolic profiling data from the literature, we provided functional GSMNs composed of an average of 2230 metabolites and 3370 reactions. Based on these GSMNs and previously published work, we propose a model for the biosynthetic pathways of the main carotenoids in these two algae. We highlight, on the one hand, the reactions and enzymes that have been preserved through evolution and, on the other hand, the specificities related to brown algae. Our data further indicate that, if abscisic acid is produced by Saccharina japonica, its biosynthesis pathway seems to be different in its final steps from that described in land plants. Thus, our work illustrates the potential of GSMNs reconstructions for formalizing hypotheses that can be further tested using targeted biochemical approaches.

Metabolic complementarity between a brown alga and associated cultivable bacteria provide indications of beneficial interactions

Brown algae are key components of marine ecosystems and live in association with bacteria that are essential for their growth and development. Ectocarpus siliculosus is a genetic and genomic model for brown algae. Here we use this model to start disentangling the complex interactions that may occur between the algal host and its associated bacteria. We report the genome-sequencing of 10 alga-associated bacteria and the genome-based reconstruction of their metabolic networks. The predicted metabolic capacities were then used to identify metabolic complementarities between the algal host and the bacteria, highlighting a range of potentially beneficial metabolite exchanges between them. These putative exchanges allowed us to predict consortia consisting of a subset of these ten bacteria that would best complement the algal metabolism. Finally, co-culture experiments were set up with a subset of these consortia to monitor algal growth as well as the presence of key algal metabolites. Although we did not fully control but only modify bacterial communities in our experiments, our data demonstrated a significant increase in algal growth in cultures inoculated with the selected consortia. In several cases, we also detected, in algal extracts, the presence of key metabolites predicted to become producible via an exchange of metabolites between the alga and the microbiome. Thus, although further methodological developments will be necessary to better control and understand microbial interactions in Ectocarpus, our data suggest that metabolic complementarity is a good indicator of beneficial metabolite exchanges in holobiont.

Unusual Patterns of Mitochondrial Inheritance in the Brown Alga Ectocarpus

Most eukaryotes inherit their mitochondria from only one of their parents. When there are different sexes, it is almost always the maternal mitochondria that are transmitted. Indeed, maternal uniparental inheritance has been reported for the brown alga Ectocarpus but we show in this study that different strains of Ectocarpus can exhibit different patterns of inheritance: Ectocarpus siliculosus strains showed maternal uniparental inheritance, as expected, but crosses using different Ectocarpus species 7 strains exhibited either paternal uniparental inheritance or an unusual pattern of transmission where progeny inherited either maternal or paternal mitochondria, but not both. A possible correlation between the pattern of mitochondrial inheritance and male gamete parthenogenesis was investigated. Moreover, in contrast to observations in the green lineage, we did not detect any change in the pattern of mitochondrial inheritance in mutant strains affected in life cycle progression. Finally, an analysis of field-isolated strains provided evidence of mitochondrial genome recombination in both Ectocarpus species.

Biotrophic interactions disentangled: In situ localisation of mRNAs to decipher plant and algal pathogen – host interactions at the single cell level

SummaryPlant-pathogen interactions follow spatiotemporal developmental dynamics where gene expression in pathogen and host undergo crucial changes. It is of great interest to detect, quantify and localise where and when key genes are active or inactive. Here, we adapt single molecule FISH techniques to demonstrate presence and activity of mRNAs using phytomyxids in their plant and algal host from laboratory and field materials. This allowed to monitor and quantify the expression of genes from the clubroot pathogen Plasmodiophora brassicae, several species of its Brassica hosts, and of several brown algae, including the genome model Ectocarpus siliculosus, infected with the phytomyxid Maullinia ectocarpii. We show that mRNAs are localised along a spatiotemporal gradient, thus providing proof-of-concept of the usefulness of these methods. These methods are easily adaptable to any interaction between microbes and their algal or plant host, and have the potential to increase our understanding of processes underpinning complex plant-microbe interactions.