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Background In the absence of sex and recombination, genomes are expected to accumulate deleterious mutations via an irreversible process known as Muller’s ratchet, especially in the case of polyploidy. In contrast, no genome-wide mutation accumulation was detected in a transcriptome of facultative apomictic, hexaploid plants of the Ranunculus auricomus complex. We hypothesize that mutations cannot accumulate in flowering plants with facultative sexuality because sexual and asexual development concurrently occurs within the same generation. We assume a strong effect of purging selection on reduced gametophytes in the sexual developmental pathway because previously masked recessive deleterious mutations would be exposed to selection. Results We test this hypothesis by modeling mutation elimination using apomictic hexaploid plants of the R. auricomus complex. To estimate mean recombination rates, the mean number of recombinants per generation was calculated by genotyping three F1 progeny arrays with six microsatellite markers and character incompatibility analyses. We estimated the strength of purging selection in gametophytes by calculating abortion rates of sexual versus apomictic development at the female gametophyte, seed and offspring stage. Accordingly, we applied three selection coefficients by considering effects of purging selection against mutations on (1) male and female gametophytes in the sexual pathway (additive, s  = 1.000), (2) female gametophytes only ( s  = 0.520), and (3) on adult plants only (sporophytes, s  = 0.212). We implemented recombination rates into a mathematical model considering the three different selection coefficients, and a genomic mutation rate calculated from genome size of our plants and plant-specific mutation rates. We revealed a mean of 6.05% recombinants per generation. This recombination rate eliminates mutations after 138, 204 or 246 generations, depending on the respective selection coefficients ( s  = 1.000, 0.520, and 0.212). Conclusions Our results confirm that the empirically observed frequencies of facultative recombination suffice to prevent accumulation of deleterious mutations via Muller’s ratchet even in a polyploid genome. The efficiency of selection is in flowering plants strongly increased by acting on the haplontic (reduced) gametophyte stage.

Hybridisation and polyploidy are major forces contributing to plant speciation. Homoploid (2x) and heteroploid (3x) hybrids, however, represent critical stages for evolution due to disturbed meiosis and reduced fertility. Apomixis – asexual reproduction via seeds – can overcome hybrid sterility, but requires several concerted alterations of developmental pathways to result in functional seed formation. Here, we analyse the reproductive behaviours of homo‐ and heteroploid synthetic hybrids from crosses between sexual diploid and tetraploid Ranunculus auricomus species to test the hypothesis that developmental asynchrony in hybrids triggers the shift to apomictic reproduction. Evaluation of male and female gametophyte development, viability and functionality of gametes shows developmental asynchrony, whereas seed set and germinability indicate reduced fitness in synthetic hybrids compared to sexual parents. We present the first experimental evidence for spontaneous apospory in most hybrids as an alternative pathway to meiosis, and the appearance of functional apomictic seeds in triploids. Bypassing meiosis permits these triploid genotypes to form viable seed and new polyploid progeny. Asynchronous development causes reduced sexual seed set and emergence of apospory in synthetic Ranunculus hybrids. Apomixis is functional in triploids and associated with drastic meiotic abnormalities. Selection acts to stabilise developmental patterns and to tolerate endosperm dosage balance shifts which facilitates successful seed set and establishment of apomictic lineages.

Ranunculus trichophyllus is an amphibious plant that produces thin and cylindrical leaves if grown under water but thick and broad leaves if grown on land. We found that such heterophylly is widely controlled by two plant hormones, abscisic acid (ABA) and ethylene, which control terrestrial and aquatic leaf development respectively. Aquatic leaves produced higher levels of ethylene but lower levels of ABA than terrestrial leaves. In aquatic leaves, their distinct traits with narrow shape, lack of stomata, and reduced vessel development were caused by EIN3-mediated overactivation of abaxial genes, RtKANADIs, and accompanying with reductions of STOMAGEN and VASCULAR-RELATED NAC-DOMAIN7 (VDN7). In contrast, in terrestrial leaves, ABI3-mediated activation of the adaxial genes, RtHD-ZIPIIIs, and STOMAGEN and VDN7 established leaf polarity, and stomata and vessel developments. Heterophylly of R.trichophyllus could be also induced by external cues such as cold and hypoxia, which is accompanied with the changes in the expression of leaf polarity genes similar to aquatic response. A closely-related land plant R. sceleratus did not show such heterophyllic responses, suggesting that the changes in the ABA/ethylene signaling and leaf polarity are one of key evolutionary steps for aquatic adaptation.

This study describes the first complete chloroplast genome of Ranunculus cf. penicillatus and provides new insights into the genetic composition and evolutionary relationships of the Ranunculus genus. The genome was assembled and characterized using high-throughput sequencing technologies, revealing a circular structure encompassing 158,313 base pairs. Comparative analysis with the chloroplast genomes of related species within the Ranunculus genus highlights notable variations in structural organization, which can elucidate potential adaptive evolutionary mechanisms. Phylogenetic analyses conducted using the maximum likelihood approach resulted in the placement of Ranunculus cf. penicillatus within a well-defined clade, revealing its relationship with other taxa. This study not only enriches the existing plastid genomic data of the genus Ranunculus but also serves as an additional resource for future studies on the phylogenetics, systematics, and conservation biology of this diverse group of aquatic plants. The findings highlight the importance of complete chloroplast genomes in the Ranunculus section Batrachium, an evolutionarily young group of aquatic plants, for understanding plant diversity and evolution. The genome can be accessed on GenBank with the accession number PV690257.

Alpine habitats are shaped by harsh abiotic conditions and cold climates. Temperature stress can affect phenotypic plasticity, reproduction, and epigenetic profiles, which may affect acclimation and adaptation. Distribution patterns suggest that polyploidy seems to be advantageous under cold conditions. Nevertheless, whether temperature stress can induce gene expression changes in different cytotypes, and how the response is initialized through gene set pathways and epigenetic control remain vague for non-model plants. The perennial alpine plant Ranunculus kuepferi was used to investigate the effect of cold stress on gene expression profiles. Diploid and autotetraploid individuals were exposed to cold and warm conditions in climate growth chambers and analyzed via transcriptome sequencing and qRT-PCR. Overall, cold stress changed gene expression profiles of both cytotypes and induced cold acclimation. Diploids changed more gene set pathways than tetraploids, and suppressed pathways involved in ion/cation homeostasis. Tetraploids mostly activated gene set pathways related to cell wall and plasma membrane. An epigenetic background for gene regulation in response to temperature conditions is indicated. Results suggest that perennial alpine plants can respond to temperature extremes via altered gene expression. Tetraploids are better acclimated to cold conditions, enabling them to colonize colder climatic areas in the Alps.

Worldwide, the genus Ranunculus includes approximately 600 species and is highly genetically diverse. Recent taxonomic reports suggest that the genus has a monophyletic origin, divided into two subgenera, and consists of 17 sections. The Central Asian country of Kazakhstan has 62 species of the genus that have primarily been collected in the central part of the country. The latest collection trips in southern parts of the country have led to the description of a wider distribution area for Ranunculus and the identification of a new species Ranunculus talassicus Schegol. et A.L. Ebel from Western Tien Shan. Therefore, in this study, attempts were made to assess the molecular taxonomic positions of R. talassicus and two other species endemic to the Central Asian region R. karkaralensis Schegol. and R. pskemensis V.N. Pavlov in relation to other species of the genus, using internal transcribed spacer (ITS) molecular genetic markers. The ITS-aligned sequences of 22 local Central Asian accessions and 43 accession sequences available in the National Center for Biotechnology Information (NCBI) database allowed the construction of a maximum parsimony phylogenetic tree and a Neighbor-Net network. The results indicated that R. talassicus and R. pskemensis could be assigned to section Ranunculastrum. Additionally, an assessment of the network suggested that R. pskemensis was the rooting taxon for the group of species containing R. talassicus, and that R. illyricus L. and R. pedatus Waldst. & Kit. were founders of a prime rooting node for the Ranunculastrum section of the genus. The ITS-aligned sequences showed that R. karkaralensis was indifferent with respect to three other species in the Ranunculus section of the genus, i.e., R. acris L., R. grandifolius C.A. Mey., and R. subborealis Tzvelev. The study indicated that the assessments of ITS-based phylogenetic tree and Neighbor-Net network provided new insights into the taxonomic positions of three endemic species from Central Asia.

Alpine plants grow in harsh environments and are thought to face occasional frost during the sensitive reproductive phase. Apomixis (asexual reproduction via seed) can be advantageous when sexual reproduction is disturbed by cold stress. Apomictic polyploids tend to grow in colder climates than their sexual diploid relatives. Whether cold temperatures actually induce apomixis was unknown to date. We tested experimentally in climate cabinets for effects of low temperatures and repeated frost on phenology, fitness and mode of reproduction in diploid and tetraploid cytotypes of the alpine species Ranunculus kuepferi. The reproduction mode was determined via flow cytometric seed screening (FCSS). Diploids produced the first flowers earlier than the tetraploids in all treatments. Cold treatments significantly reduced the fitness of both cytotypes regarding seed set, and increased the frequency of apomictic seed formation in diploids, but not in tetraploids. Over consecutive years, the degree of facultative apomixis showed individual phenotypic plasticity. Cold stress is correlated to expression of apomixis in warm-adapted, diploid R. kuepferi, while temperature-tolerant tetraploids just maintain facultative apomixis as a possible adaptation to colder climates. However, expression of apomixis may not depend on polyploidy, but rather on failure of the sexual pathway.

In this study, the seed germination and dormancy characteristics of three Ranunculus species native to Korea ( R. cantoniensis , R. chinensis , and R. sceleratus ) were determined to establish an effective dormancy-breaking protocol. The results revealed that the R. cantoniensis , R. chinensis , and R. sceleratus seeds responded differently to treatment with gibberellins (GAs) and stratification. Warm stratification at 20℃ increased the germination percentage and partially broke the dormancy of the R. cantoniensis seeds; moreover, the germination temperature range of the seeds expanded upon treatment with high-concentration GA 4 + 7 . Meanwhile, neither cold nor warm stratification was effective at breaking the dormancy of R. chinensis seeds; however, high-concentration GA 4 + 7 treatment broke the dormancy of the seeds by expanding the germination temperature range. Lastly, the R. sceleratus seeds did not respond to the treatment with GAs; however, their germination percentage increased after undergoing warm stratification at 25℃. The seeds of these three species were characterized as exhibiting nondeep morphophysiological dormancy. The findings of this study enhance our understanding of the temperature-related germination responses of the three Ranunculus species, offering valuable insights into their conservation and utilization.

Ranunculus glacialis grows and reproduces successfully, although the snow-free time period is short (2–3 months) and night frosts are frequent. At a nival site (3185 m a.s.l.), we disentangled the interplay between the atmospheric temperature, leaf temperatures, and leaf freezing frequency to assess the actual strain. For a comprehensive understanding, the freezing behavior from the whole plant to the leaf and cellular level and its physiological after-effects as well as cell wall chemistry were studied. The atmospheric temperatures did not mirror the leaf temperatures, which could be 9.3 °C lower. Leaf freezing occurred even when the air temperature was above 0 °C. Ice nucleation at on average −2.6 °C started usually independently in each leaf, as the shoot is deep-seated in unfrozen soil. All the mesophyll cells were subjected to freezing cytorrhysis. Huge ice masses formed in the intercellular spaces of the spongy parenchyma. After thawing, photosynthesis was unaffected regardless of whether ice had formed. The cell walls were pectin-rich and triglycerides occurred, particularly in the spongy parenchyma. At high elevations, atmospheric temperatures fail to predict plant freezing. Shoot burial prevents ice spreading, specific tissue architecture enables ice management, and the flexibility of cell walls allows recurrent freezing cytorrhysis. The peculiar patterning of triglycerides close to ice rewards further investigation.

Generalist herbivorous insects, which feed on plant tissue that is nutritionally heterogeneous or varies in its content of secondary metabolites, often benefit from dietary mixing through more balanced nutrient intake or reduced exposure to harmful secondary metabolites. Pollen is similarly heterogeneous as other plant tissue in its content of primary and secondary metabolites, suggesting that providing their offspring with mixed pollen diets might be a promising strategy for pollen generalist bees to complement nutrient imbalances or to mitigate harmful secondary metabolites of unfavourable pollen. In the present study, we compared larval performance of the pollen generalist solitary bee species Osmia cornuta (Megachilidae) on five experimental pollen diets that consisted of different proportions of unfavourable pollen diet of Ranunculus acris (Ranunculaceae) and favourable pollen diet of Sinapis arvensis (Brassicaceae). In addition, we microscopically analysed the pollen contained in the scopal brushes of field‐collected females of O. cornuta and three closely related species to elucidate to what degree these pollen generalist bees mix pollen of different hosts in their brood cells. In striking contrast to a pure Ranunculus pollen diet, which had a lethal effect on most developing larvae of O. cornuta, larval survival, larval development time and adult body mass of both males and females remained nearly unaffected by the admixture of up to 50% of Ranunculus pollen diet to the larval food. Between 42% and 66% of all female scopal pollen loads analysed contained mixtures of pollen from two to six plant families, indicating that pollen mixing is a common behaviour in O. cornuta and the three related bee species. The present study provides the first evidence that the larvae of pollen generalist bees can benefit from the nutrient content of unfavourable pollen without being negatively affected by its unfavourable chemical properties if such pollen is mixed with favourable pollen. We conclude that the widespread pollen mixing by females of pollen generalist bees should also be considered as a possible strategy to exploit flowers with unfavourable pollen and to optimize larval food quality.