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• The bipolar spindle structure in meiosis is essential for faithful chromosome segregation. PUTATIVE RECOMBINATION INITIATION DEFECT 1 (PRD1) previously has been shown to participate in the formation of DNA double strand breaks (DSBs). However, the role of PRD1 in meiotic spindle assembly has not been elucidated. • Here, we reveal by both genetic analysis and immunostaining technology that PRD1 is involved in spindle assembly in rice (Oryza sativa) meiosis. • We show that DSB formation and bipolar spindle assembly are disturbed in prd1 meiocytes. PRD1 signals display a dynamic pattern of localization from covering entire chromosomes at leptotene to congregating at the centromere region after leptotene. Centromeric localization of PRD1 signals depends on the organization of leptotene chromosomes, but not on DSB formation and axis establishment. PRD1 exhibits interaction and co-localization with several kinetochore components. We also find that bi-orientation of sister kinetochores within a univalent induced by mutation of REC8 can restore bipolarity in prd1. Furthermore, PRD1 directly interacts with REC8 and SGO1, suggesting that PRD1 may play a role in regulating the orientation of sister kinetochores. • Taken together, we speculate that PRD1 promotes bipolar spindle assembly, presumably by modulating the orientation of sister kinetochores in rice meiosis.

The last glacial period is characterized by a number of millennial climate events that have been identified in both Greenland and Antarctic ice cores and that are abrupt in Greenland climate records. The mechanisms governing this climate variability remain a puzzle that requires a precise synchronization of ice cores from the two hemispheres to be resolved. Previously, Greenland and Antarctic ice cores have been synchronized primarily via their common records of gas concentrations or isotopes from the trapped air and via cosmogenic isotopes measured on the ice. In this work, we apply ice core volcanic proxies and annual layer counting to identify large volcanic eruptions that have left a signature in both Greenland and Antarctica. Generally, no tephra is associated with those eruptions in the ice cores, so the source of the eruptions cannot be identified. Instead, we identify and match sequences of volcanic eruptions with bipolar distribution of sulfate, i.e. unique patterns of volcanic events separated by the same number of years at the two poles. Using this approach, we pinpoint 82 large bipolar volcanic eruptions throughout the second half of the last glacial period (12–60 ka). This improved ice core synchronization is applied to determine the bipolar phasing of abrupt climate change events at decadal-scale precision. In response to Greenland abrupt climatic transitions, we find a response in the Antarctic water isotope signals (δ18O and deuterium excess) that is both more immediate and more abrupt than that found with previous gas-based interpolar synchronizations, providing additional support for our volcanic framework. On average, the Antarctic bipolar seesaw climate response lags the midpoint of Greenland abrupt δ18O transitions by 122±24 years. The time difference between Antarctic signals in deuterium excess and δ18O, which likewise informs the time needed to propagate the signal as described by the theory of the bipolar seesaw but is less sensitive to synchronization errors, suggests an Antarctic δ18O lag behind Greenland of 152±37 years. These estimates are shorter than the 200 years suggested by earlier gas-based synchronizations. As before, we find variations in the timing and duration between the response at different sites and for different events suggesting an interaction of oceanic and atmospheric teleconnection patterns as well as internal climate variability.

Glaciers are inhabited by various cryophilic organisms ranging from single celled to multicellular, like Tardigrada (water bears). Owing to their scattered distribution, glaciers represent extremely fragmented habitats, and it remains unclear how their inhabitants survive and disperse among such isolated patches. This study investigates the biogeography of the tardigrade genus Cryoconicus, whose distribution, population stability, and interregional connectivity are examined by screening the collections from ~ 60 glaciers worldwide and by a phylogeographic analysis. We found that two Cryoconicus species occur at low densities on two Arctic glaciers in Svalbard, far from their previously reported Antarctic and Central Asian ranges. Screening of worldwide databases and DNA metabarcoding indicated that these species are absent or rare in the intermediate areas, suggesting large disjunctions in their ranges. In particular, the genetic data and multiyear resampling showed that Cryoconicus kaczmareki established a stable population on the Ebba Glacier (Svalbard), which has been isolated from its Asian core range since before the last glacial maximum. Our findings suggest that glacial invertebrates may possess wide yet largely disjunctive ranges. Interpolar- or intercontinental-scale movements of cryophilic meiofauna may occur, but migration connectivity is not sufficient to mitigate the differentiation of the local population. Revealed biogeographic patterns further demonstrate that inhabitants of extreme environments may establish isolated and highly fragmented populations that persist long term, even if at very low densities.

The occurrence of species in both polar regions (bipolarity) is a common phenomenon in the Antarctic flora. Considering the high morphological variation in polar regions due to extreme conditions, the use of molecular tools is indispensable for testing whether Arctic and Antarctic populations indeed belong to the same species. However, few phylogeographic studies of bipolar bryophytes have been conducted so far, especially when comparing molecular and morphological variation. Here, we assess the bipolarity and intraspecific variation of Roaldia revoluta, a strictly bipolar species of pleurocarpous mosses. Phylogenetic analyses based on ITS sequences clearly resolve R. revoluta as monophyletic and confirm its bipolar distribution pattern. Low intraspecific molecular variation in the markers ITS/26S and rpl16 was observed, and most specimens from both polar regions belong to a single haplotype, making it difficult to infer the origin and dispersal routes between both polar regions of R. revoluta. Morphometric analysis furthermore suggests that there are no significant morphological differences among populations from both polar regions and that morphological variation is mainly influenced by local environmental conditions. Our data do not unequivocally support the recent separation of the former intraspecific taxon Hypnum revolutum var. dolomiticum at the species level as Roaldia dolomitica.

Compared to other organisms, such as vascular plants or mosses, lichen-forming fungi have a high number of species occurring in both northern and southern hemispheres but are largely absent from intermediate, tropical latitudes. For instance, ca. 160 Antarctic species also occur in polar areas or mountainous temperate regions of the northern hemisphere. Early interpretations of this particular distribution pattern were made in terms of vicariance or long-distance dispersal. However, it was not until the emergence of phylogenetics and the possibility of dating past diversification and colonization events that these initial hypotheses started to be evaluated. The premise of a relatively recent colonization of the southern hemisphere by boreal lichens through long-distance dispersal has gained support in recent studies based on either the comparison of genetic affinities (i.e., tree topology) or more robust, statistical migratory models. Still, the scarcity of such studies and a concern that taxonomic concepts for bipolar lichens are often too broad preclude the generation of sound explanations on the mechanisms and origin of such fascinating disjunct distributions. This review provides an up-to-date overview of bipolar distributions in lichen-forming fungi and their photobionts. Evidence provided by recent, molecular-based studies as well as data on the type of lichen reproduction, dispersal ability, photobiont identity and availability, and habitat preferences are brought together to discuss how and when these distributions originated and their genetic footprints. Ideas for future prospects and research are also discussed.

ABSTRACT Polar glacier forefields offer an unprecedented framework for studying community assembly processes in regions that are geographically and climatically isolated. Through amplicon sequence variant (ASV) inference, we compared the composition and structure of soil bacterial communities from glacier forefields in Iceland and Antarctica to assess overlap between communities and the impact of established cryptogamic covers on the uniqueness of their taxa. These pioneer microbial communities were found to share only 8% of ASVs and each taxonomic group's contribution to the shared ASV data subset was heterogeneous and independent of their relative abundance. Although the presence of ASVs specific to one glacier forefield and/or different cryptogam cover values confirms the existence of habitat specialist bacteria, our data show that the influence of cryptogams on the edaphic bacterial community structure also varied also depending on the taxonomic group. Hence, the establishment of distinct cryptogamic covers is probably not the only factor driving the uniqueness of bacterial communities at both poles. The structure of bacterial communities colonising deglaciated areas seems also conditioned by lineage-specific limitations in their dispersal capacity and/or their establishment and persistence in these isolated and hostile regions. Soils of Antarctic and Icelandic glacier forefields share few bacterial lineages and both are dominated by habitat specialists.

Aim: The hypotheses proposed to explain the high percentage of bipolar lichens in Antarctica have never been explicitly tested. We used the strictly bipolar, coastal lichenized fungus Mastodia tessellata (Verrucariaceae, Ascomycota) and its photobionts (Prasiola, Trebouxiophyceae, Chlorophyta) as model species to discern whether this extraordinary disjunction originated from vicariance or long-distance dispersal. Location: Coasts of Antarctica, Tierra del Fuego (Chile), Alaska (USA) and British Columbia (Canada). Methods: Based on a comprehensive geographical (315 specimens and 16 populations from Antarctica, Tierra del Fuego and North America) and molecular sampling (three and four loci for the fungus and algae respectively), we implemented explicit Bayesian methods to compare alternative hypotheses of speciation and migration, and performed dating analyses for the fungal and algal partner, in order to infer the timing of the colonization events and the direction of gene flow among distant, disjunct areas. Results: Mastodia tessellata comprises two fungal species which in turn associate with three photobiont lineages along the studied distribution range. Independent estimation of divergence ages for myco- and photobionts indicated a middle to latest Miocene species split in the Southern Hemisphere, and a late Miocene to Pleistocene acquisition of the bipolar distribution. Comparison of migration models and genetic diversity patterns suggested an austral origin for the bipolar species. Main conclusions: The complex evolutionary history of Mastodia tessellata s.l. can be explained by a combination of vicariant and long-distance dispersal mechanisms. We provide novel evidence of a pre-Pleistocene long-term evolution of lichens in Antarctica as well as for bipolar distributions shaped by Southern to Northern Hemisphere migratory routes without the need for stepping stones.

To date, a total of 23 valid species of heteronemerteans belonging to 15 genera have been recorded in Antarctic and Subantarctic waters. The ribbon worm Heteronemertes longifissa (Hubrecht, 1887) is the only heteronemertean species reported to have bipolar distribution, but this statement is doubtful. The phylogenetic relationships of H. longifissa to other heteronemerteans remain uncertain. A genetic analysis of specimens from Antarctica has shown that the name H. longifissa refers to two sibling species with an uncorrected p-distance of 5.3% in COI. These species differ in body color: one is whitish, and the other is grayish-pink. The species with the whitish body has been reliably identified from off the Norway coast (as Cerebratulus sp. NemBar1383 (BOLD: ACM5920)), i.e., it has a bipolar distribution. A molecular phylogenetic analysis of Lineidae based on five gene markers (COI, 16S, 18S, 28S, and histone H3) has shown the genus Heteronemertes to belong to Lineage D of Clade 2 sensu Kajihara et al., 2022 (crown Lineidae). The phylogenetic positions of four more species of unidentified lineids are currently under discussion.

Two new species of the genus Lecidella, one with a North American-maritime Antarctic distribution and one with a so far exclusively southern South American-maritime Antarctic distribution, are described using molecular and morphological tools. Lecidella ayazii is a species growing on soil and also on mosses and has so far been found on the Antarctic Peninsula, as well as in the alpine areas of the La Sal Mountains, Utah, USA and in the Kivalliq Region (Nunavut) in the north of Canada, whereas L. drakensis occurs mainly on siliceous rocks, rarely on mosses, and has been recorded on both sides of the Drake Passage in southern Patagonia and the Antarctic Peninsula. Phylogenetic analysis of the nrITS sequence data shows that both species belong in the L. elaeochroma clade, each forming a highly supported and distinct group. Furthermore, they also differ in morphological and chemical characters from the species described so far in this clade. In addition, five further accessions were recorded from the maritime Antarctic, which were placed in the cosmopolitan and heterogeneous L. stigmatea clade, of which one could be assigned to the bipolar species L. siplei.

The phytohormones cytokinin and auxin orchestrate the root meristem development in angiosperms by determining embryonic bipolarity. Ferns, having the most basal euphyllophyte root, form neither bipolar embryos nor permanent embryonic primary roots but rather an adventitious root system. This raises the questions of how auxin and cytokinin govern fern root system architecture and whether this can tell us something about the origin of that root. Using Azolla filiculoides, we characterized the influence of IAA and zeatin on adventitious fern root meristems and vasculature by Nomarski microscopy. Simultaneously, RNAseq analyses, yielding 36 091 contigs, were used to uncover how the phytohormones affect root tip gene expression. We show that auxin restricts Azolla root meristem development, while cytokinin promotes it; it is the opposite effect of what is observed in Arabidopsis. Global gene expression profiling uncovered 145 genes significantly regulated by cytokinin or auxin, including cell wall modulators, cell division regulators and lateral root formation coordinators. Our data illuminate both evolution and development of fern roots. Promotion of meristem size through cytokinin supports the idea that root meristems of euphyllophytes evolved from shoot meristems. The foundation of these roots was laid in a postembryonically branching shoot system.