Tempo and drivers of plant diversification in the European mountain system.

There is still limited consensus on the evolutionary history of species-rich temperate alpine floras due to a lack of comparable and high-quality phylogenetic data covering multiple plant lineages. Here we reconstructed when and how European alpine plant lineages diversified, i.e., the tempo and drivers of speciation events. We performed full-plastome phylogenomics and used multi-clade comparative models applied to six representative angiosperm lineages that have diversified in European mountains (212 sampled species, 251 ingroup species total). Diversification rates remained surprisingly steady for most clades, even during the Pleistocene, with speciation events being mostly driven by geographic divergence and bedrock shifts. Interestingly, we inferred asymmetrical historical migration rates from siliceous to calcareous bedrocks, and from higher to lower elevations, likely due to repeated shrinkage and expansion of high elevation habitats during the Pleistocene. This may have buffered climate-related extinctions, but prevented speciation along elevation gradients as often documented for tropical alpine floras.

Discovery of cryptic plant diversity on the rooftops of the Alps.

High elevation temperate mountains have long been considered species poor owing to high extinction or low speciation rates during the Pleistocene. We performed a phylogenetic and population genomic investigation of an emblematic high-elevation plant clade (Androsace sect. Aretia, 31 currently recognized species), based on plant surveys conducted during alpinism expeditions. We inferred that this clade originated in the Miocene and continued diversifying through Pleistocene glaciations, and discovered three novel species of Androsace dwelling on different bedrock types on the rooftops of the Alps. This highlights that temperate high mountains have been cradles of plant diversity even during the Pleistocene, with in-situ speciation driven by the combined action of geography and geology. Our findings have an unexpected historical relevance: H.-B. de Saussure likely observed one of these species during his 1788 expedition to the Mont Blanc and we describe it here, over two hundred years after its first sighting.

The Treasure Vault Can be Opened: Large-Scale Genome Skimming Works Well Using Herbarium and Silica Gel Dried Material.

Genome skimming has the potential for generating large data sets for DNA barcoding and wider biodiversity genomic studies, particularly via the assembly and annotation of full chloroplast (cpDNA) and nuclear ribosomal DNA (nrDNA) sequences. We compare the success of genome skims of 2051 herbarium specimens from Norway/Polar regions with 4604 freshly collected, silica gel dried specimens mainly from the European Alps and the Carpathians. Overall, we were able to assemble the full chloroplast genome for 67% of the samples and the full nrDNA cluster for 86%. Average insert length, cover and full cpDNA and rDNA assembly were considerably higher for silica gel dried than herbarium-preserved material. However, complete plastid genomes were still assembled for 54% of herbarium samples compared to 70% of silica dried samples. Moreover, there was comparable recovery of coding genes from both tissue sources (121 for silica gel dried and 118 for herbarium material) and only minor differences in assembly success of standard barcodes between silica dried (89% ITS2, 96% matK and rbcL) and herbarium material (87% ITS2, 98% matK and rbcL). The success rate was > 90% for all three markers in 1034 of 1036 genera in 160 families, and only Boraginaceae worked poorly, with 7 genera failing. Our study shows that large-scale genome skims are feasible and work well across most of the land plant families and genera we tested, independently of material type. It is therefore an efficient method for increasing the availability of plant biodiversity genomic data to support a multitude of downstream applications.

Differences in the fungal communities nursed by two genetic groups of the alpine cushion plant, Silene acaulis.

Foundation plants shape the composition of local biotic communities and abiotic environments, but the impact of a plant's intraspecific variations on these processes is poorly understood. We examined these links in the alpine cushion moss campion (Silene acaulis) on two neighboring mountain ranges in the French Alps. Genotyping of cushion plants revealed two genetic clusters matching known subspecies. The exscapa subspecies was found on both limestone and granite, while the longiscapa one was only found on limestone. Even on similar limestone bedrock, cushion soils from the two S. acaulis subspecies deeply differed in their impact on soil abiotic conditions. They further strikingly differed from each other and from the surrounding bare soils in fungal community composition. Plant genotype variations accounted for a large part of the fungal composition variability in cushion soils, even when considering geography or soil chemistry, and particularly for the dominant molecular operational taxonomic units (MOTUs). Both saprophytic and biotrophic fungal taxa were related to the MOTUs recurrently associated with a single plant genetic cluster. Moreover, the putative phytopathogens were abundant, and within the same genus (Cladosporium) or species (Pyrenopeziza brassicae), MOTUs showing specificity for each plant subspecies were found. Our study highlights the combined influences of bedrock and plant genotype on fungal recruitment into cushion soils and suggests the coexistence of two mechanisms, an indirect selection resulting from the colonization of an engineered soil by free-living saprobes and a direct selection resulting from direct plant-fungi interactions.

Understanding the evolution of holoparasitic plants: the complete plastid genome of the holoparasite Cytinus hypocistis (Cytinaceae).

Background and Aims Plant plastid genomes are highly conserved in size, gene content and structure; however, parasitic plants are a noticeable exception to this evolutionary stability. Although the evolution of parasites could help to better understand plastome evolution in general, complete plastomes of parasites have been sequenced only for some lineages so far. Here we contribute to filling this gap by providing and analysing the complete plastome sequence of Cytinus hypocistis, the first parasite sequenced for Malvales and a species suspected to have an extremely small genome. Methods We sequenced and assembled de novo the plastid genome of Cytinus hypocistis using a shotgun approach on genomic DNA. Phylogenomic analyses based on coding regions were performed on Malvidae. For each coding region present in Cytinus, we tested for relaxation or intensification of selective pressures in the Cytinus lineage compared with autotrophic Malvales. Key Results Cytinus hypocistis has an extremely divergent genome that is among the smallest sequenced to date (19·4 kb), with only 23 genes and no inverted repeat regions. Phylogenomic analysis confirmed the position of Cytinus within Malvales. All coding regions of Cytinus plastome presented very high substitution rates compared with non-parasitic Malvales. Conclusions Some regions were inferred to be under relaxed negative selection in Cytinus, suggesting that further plastome reduction is occurring due to relaxed purifying selection associated with the loss of photosynthetic activity. On the other hand, increased selection intensity and strong positive selection were detected for rpl22 in the Cytinus lineage, which might indicate an evolutionary role in the host-parasite arms race, a point that needs further research.

Is There Any Evidence for Rapid, Genetically-Based, Climatic Niche Expansion in the Invasive Common Ragweed?

Climatic niche shifts have been documented in a number of invasive species by comparing the native and adventive climatic ranges in which they occur. However, these shifts likely represent changes in the realized climatic niches of invasive species, and may not necessarily be driven by genetic changes in climatic affinities. Until now the role of rapid niche evolution in the spread of invasive species remains a challenging issue with conflicting results. Here, we document a likely genetically-based climatic niche expansion of an annual plant invader, the common ragweed (Ambrosia artemisiifolia L.), a highly allergenic invasive species causing substantial public health issues. To do so, we looked for recent evolutionary change at the upward migration front of its adventive range in the French Alps. Based on species climatic niche models estimated at both global and regional scales we stratified our sampling design to adequately capture the species niche, and localized populations suspected of niche expansion. Using a combination of species niche modeling, landscape genetics models and common garden measurements, we then related the species genetic structure and its phenotypic architecture across the climatic niche. Our results strongly suggest that the common ragweed is rapidly adapting to local climatic conditions at its invasion front and that it currently expands its niche toward colder and formerly unsuitable climates in the French Alps (i.e. in sites where niche models would not predict its occurrence). Such results, showing that species climatic niches can evolve on very short time scales, have important implications for predictive models of biological invasions that do not account for evolutionary processes.

Depletion of yeast PDK1 orthologs triggers a stress-like transcriptional response.

BACKGROUND: Pkh proteins are the PDK1 orthologs in S. cerevisiae. They have redundant and essential activity and are responsible for the phosphorylation of several members of the AGC family of protein kinases. Pkh proteins have been involved in several cellular functions, including cell wall integrity and endocytosis. However the global expression changes caused by their depletion are still unknown. RESULTS: A doxycycline-repressible tetO7 promoter driving the expression of PKH2 in cells carrying deletions of the PKH1 and PKH3 genes allowed us to progressively deplete cells from Pkh proteins when treated with doxycycline. Global gene expression analysis indicate that depletion of Pkh results in the up-regulation of genes involved in the accumulation of glycogen and also of those related to stress responses. Moreover, genes involved in the ion transport were quickly down-regulated when the levels of Pkh decreased. The reduction in the mRNA levels required for protein translation, however, was only observed after longer doxycycline treatment (24 h). We uncovered that Pkh is important for the proper transcriptional response to heat shock, and is mostly required for the effects driven by the transcription factors Hsf1 and Msn2/Msn4, but is not required for down-regulation of the mRNA coding for ribosomal proteins. CONCLUSIONS: By using the tetO7 promoter we elucidated for the first time the transcriptomic changes directly or indirectly caused by progressive depletion of Pkh. Furthermore, this system enabled the characterization of the transcriptional response triggered by heat shock in wild-type and Pkh-depleted cells, showing that about 40 % of the observed expression changes were, to some degree, dependent on Pkh.