Annals of botany最新文献

Background and aims: Plant regeneration by seeds is driven by a set of physiological traits, many of which show functional intraspecific variation along biogeographical gradients. In many species, germination phenology depends on a germination delay imposed by the need for post-dispersal embryo growth (a.k.a. morphological dormancy). Such growth occurs as a function of environmental temperatures and shows base, optimum and ceiling temperatures (i.e. cardinal temperatures or thermal thresholds). However, the biogeographical variation in such thresholds has not been tested.

Methods: We used a thermal time approach and field experiments to assess intraspecific variation at the continental scale in the embryo growth thermal thresholds of the geophyte Conopodium majus (Apiaceae) across its distribution from the Iberian Peninsula to Scandinavia.

Key results: Thermal thresholds for embryo growth varied across the latitudinal gradient, with estimated optimum temperatures between 2.5 and 5.2 °C, ceiling temperatures between 12 and 20.5 °C, and base temperatures between -6.6 and -2.7 °C. Germination in the field peaked in January and February. The limiting factor for embryo growth was the ceiling temperature, which was negatively correlated with latitude and the bioclimatic environment of each population. In contrast, the optimal and base temperature were independent of local climate.

Conclusions: These results indicate that thermal thresholds for embryo growth are functional ecophysiological traits that drive seed germination phenology and seed responses to the soil climatic environment. Therefore, post-dispersal embryo growth can be a key trait impacting climate change effects on phenology and species distributions.

Background and aims: To better understand C4 evolution in monocots, we characterized C3-C4 intermediate phenotypes in the grass genus Homolepis (subtribe Arthropogoninae).

Methods: Carbon isotope ratio (δ13C), leaf gas exchange, mesophyll (M) and bundle sheath (BS) tissue characteristics, organelle size and numbers in M and BS tissue, and tissue distribution of the P-subunit of glycine decarboxylase (GLDP) were determined for five Homolepis species and the C4 grass Mesosetum loliiforme from a phylogenetic sister clade. We generated a transcriptome-based phylogeny for Homolepis and Mesosetum species to interpret physiological and anatomical patterns in an evolutionary context, and to test for hybridization.

Key results: Homolepis contains two C3 species (H. glutinosa, H. villaricensis), one species with a weaker form of C2 termed sub-C2 (H. isocalycia), and two C2 species (H. longispicula, H. aturensis). Homolepis longispicula and H. aturensis express over 85 % of leaf glycine in centripetal mitochondria within the BS, and have increased fractions of leaf chloroplasts, mitochondria and peroxisomes within the BS relative to H. glutinosa. Analysis of leaf gas exchange, cell ultrastructure and transcript expression show M. loliiforme is a C4 plant of the NADP-malic enzyme subtype. Homolepis comprises two sister clades, one containing H. glutinosa and H. villaricensis and the second H. longispicula and H. aturensis. Homolepis isocalycia is of hybrid origin, its parents being H. aturensis and a common ancestor of the C3  Homolepis clade and H. longispicula.

Conclusions: Photosynthetic activation of BS tissue in the sub-C2 and C2 species of Homolepis is similar to patterns observed in C3-C4 intermediate eudicots, indicating common evolutionary pathways from C3 to C4 photosynthesis in these disparate clades. Hybridization can diversify the C3-C4 intermediate character state and should be considered in reconstructing putative ancestral states using phylogenetic analyses.

Background: Floral adaptations supposedly help pollen grains to cross the numerous barriers faced during their journey to stigmas. Stamen dimorphism and specialized petals, like the cucculus in the Cassieae tribe (Fabaceae), are commonly observed in flowers that offer only pollen as a resource for bee pollinators. Here, we experimentally investigated whether stamen dimorphism and the cucculus enhance pollen placement on the bee's body.

Methods: We used 3-D-printed bee models to apply artificial vibrations to the flowers of Chamaechrista latistipula with their cucculus deflected or maintained in its original position and their anther pores manipulated. After each simulated flower visit, we captured photographs of the artificial bee from four distinct angles. Employing digital imaging techniques, we documented the presence and location of pollen and stigma on the bee's body.

Key results: Our findings reveal that the cucculus redistributes pollen grains on the bee's body. There is a remarkable increase in pollen density (~10-fold) on the lateral side adjacent to the cucculus, precisely where the stigma contacts the bee when the cucculus is unmanipulated. Furthermore, the cucculus also enhances pollen placement on the ventral region of the bee, indicating its additional function. The cucculus also increases the accuracy of pollen grains on the adjacent lateral region of the bee's body, irrespective of the pollen grains released by small or large anthers.

Conclusions: Floral specialized traits, such as modified petals and stamen dimorphism, can modify the fate of pollen grains and ultimately contribute to male reproductive performance in pollen flowers with poricidal anthers. The cucculus exhibits a dual role by promoting pollen placement in optimal regions for pollination and probably supporting pollen grains for bee feeding. These findings provide valuable insights into the adaptive significance of floral traits and their impact on the reproductive success of pollen flowers.

Background and aims: The transformation of sieve elements from meristematic cells, equipped with a full complement of organelles, to specialized transport tubes devoid of a nucleus has long been enigmatic. We hypothesized a strong involvement of various degradation pathways, particularly macroautophagy in this context, emphasizing the importance of autophagic selectivity in the remaining viability of these cells.

Methods: Experiments were performed on pioneer roots of Populus trichocarpa cultivated in rhizotrons under field conditions. Through anatomical, ultrastructural and molecular analyses, we delineate the stages of phloemogenesis and the concurrent alterations in the cytoplasmic composition of SEs.

Key results: Notably, we observed not only macroautophagic structures, but also the formation of autophagic plastids, the selective degradation of specific organelles, vacuole disruption and the release of vacuolar contents. These events initially lead to localized reductions in cytoplasm density, but the organelle-rich cytoplasmic phase is safeguarded from extensive damage by a membrane system derived from the endoplasmic reticulum. The sieve element ultimately develops into a conduit containing electron-translucent cytoplasm. Eventually, the mature sieve element is a tube filled only by translucent cytoplasm, with sparse organelles tethered to the cell wall.

Conclusions: Although the activation of programmed cell death pathways was postulated, the persistence of sieve elements indicates that protoplast depletion is meticulously regulated by hitherto unidentified mechanisms. This research elucidates the sequential processes occurring in these cells during phloemogenesis and unveils novel insights into the mechanisms of selective autophagy.

Background and aims: Both plants and animals display considerable variation in their phenotypic traits as they grow. This variation helps organisms to adapt to specific challenges at different stages of development. Masting, the variable and synchronized seed production across years by a population of plants, is a common reproductive strategy in perennial plants that can enhance reproductive efficiency through increasing pollination efficiency and decreasing seed predation. Masting represents a population-level phenomenon generated from individual plant behaviours. While the developmental trajectory of individual plants influences their masting behaviour, the translation of such changes into benefits derived from masting remains unexplored.

Methods and key results: We used 43 years of seed production monitoring in European beech (Fagus sylvatica) to address that gap. The largest improvements in reproductive efficiency from masting happen in the largest trees. Masting leads to a 48-fold reduction in seed predation in large trees compared with 28-fold in small trees. Masting yields a 6-fold increase in pollination efficiency in large trees compared with 2.5-fold in small trees. Paradoxically, although the largest trees show the biggest reproductive efficiency benefits from masting, large trees mast less strongly than small trees.

Conclusions: Apparently suboptimal allocation of effort across years by large plants may be a consequence of anatomical constraints or bet-hedging. Ontogenetic shifts in individual masting behaviour and associated variable benefits have implications for the reproductive potential of plant populations as their age distribution changes, with applications in plant conservation and management.

Background and aims: Oophytum (Aizoaceae) is a locally endemic genus of the extremely fast-evolving subfamily Ruschioideae and consists of only two formally accepted species (Oophytum nanum and Oophytum oviforme). Both species are leaf-succulent dwarf shrubs and habitat specialists on quartz fields in the Knersvlakte, a renowned biodiversity hotspot in the arid winter-rainfall Succulent Karoo Biome of South Africa. Quartz fields present specialised patchy habitats with an island-like distribution in the landscape. Oophytum oviforme grows in the south-western part, whereas O. nanum covers most of the remaining Knersvlakte. These species co-occur in a small area, but within different quartz islands. We investigated the effects of the patchy distribution, environmental conditions and potential effects of palaeoclimatic changes on the genetics of Oophytum.

Methods: Phylogenetic and population genetic analyses of 35 populations of the genus, covering its entire distribution area, were conducted using four chloroplast DNA markers and an amplified fragment length polymorphism dataset. These were combined with environmental data via a principal component analysis and comparative heatmap analyses.

Key results: The genetic pattern of the Oophytum metapopulation is a tripartite division, with northern, central and western groups. This geographical pattern does not correspond to the two-species concept of Oophytum. Only the western O. oviforme populations form a monophyletic lineage, whereas the central populations of O. oviforme are genetic hybrids of O. nanum populations. The highly restricted gene flow often resulted in private gene pools with very low genetic diversity, in contrast to the hybrid gene pools of the central and edge populations.

Conclusions: Oophytum is an exceptional example of an extremely fast-evolving genus that illustrates the high speciation rate of the Ruschioideae and their success as one of the leading plant groups of the drought-prone Succulent Karoo Biome. The survival strategy of these dwarf quartz-field endemics is an interplay of adaptation to diverse island habitats, highly restricted gene flow, occasional long-distance dispersal, migration, founder effects and hybridisation events within a small and restricted area caused by glacial and interglacial changing climate conditions from the Pleistocene to the Present. These findings have important implications for future conservation management strategies.

Background: Modern biotechnology is one of the last century's major advances in human science. Particularly in the agronomical field, the landscape of crop improvement technologies has witnessed a great expansion, driven by the integration of molecular and genetic engineering methodologies into the breeding toolbox. Latin America (LATAM) serves as a pioneering region in incorporating such techniques with several countries swiftly embracing these technologies.

Scope: This review aims to give a comprehensive overview of the elements that influenced agrobiotech acceptance in LATAM countries and how such cases could provide support for upcoming technologies to be considered worldwide.

Conclusions: Nearly 50 years of biotech breakthroughs have provided humankind with an impressive portfolio of tools already integrated into several life-science areas. The agronomical field has greatly progressed thanks to technologies derived from genetically modified organisms and great promises are being made to also incorporate genome-editing products. LATAM provides a prime example of how early introduction of novelties in the crop production chain can result in improved yields, paving the way for future developments to be easily integrated into the technological ecosystem of a region. The example set by LATAM can also be useful for the present gene-editing regulatory scenario. With several countries presently on the path to approving these methods in their current crop systems, basing their next steps on the example of LATAM could represent a safe and practical pathway towards a new agronomical revolution.

Background and aims: Assessing adaptive genetic variation and its spatial distribution is crucial to conserve forest genetic resources and manage species' adaptive potential. Macro-environmental gradients commonly exert divergent selective pressures that enhance adaptive genetic divergence among populations. Steep micro-environmental variation might also result in adaptive divergence at finer spatial scales, even under high gene flow, but it is unclear how often this is the case. Here, we assess genetic variation in early-fitness traits among distant and nearby maritime pine (Pinus pinaster) populations, to investigate climatic factors associated with trait divergence, and to examine trait integration during seedling establishment.

Methods: Open pollinated seeds were collected from seven population pairs across the European species distribution, with paired populations spatially close (between <1 and 21 km) but environmentally divergent. Seeds were sown in semi-natural conditions at three environmentally contrasting sites, where we monitored seedling emergence, growth and survival.

Key results: At large spatial scales, we found significant genetic divergence among populations in all studied traits, with certain traits exhibiting an association with temperature and precipitation gradients. Significant trait divergence was also detected between pairs of nearby populations. In addition, we found consistent trait correlations across experimental sites; notably, heavier seeds and earlier seedling emergence were both associated with higher seedling survival and fitness over two years in all experimental conditions.

Conclusions: We identified mean annual temperature and precipitation seasonality as potential drivers of P. pinaster population divergence in the studied early-life traits. Populations genetically diverge also at local spatial scales, potentially suggesting that divergent natural selection can override gene flow along local-scale ecological gradients. These results suggest the species exhibits substantial adaptive potential that has allowed it to survive and evolve under contrasting environmental conditions.

Background and aims: Morphological differences between the two genetically close wild radishes, Raphanus raphanistrum and R. pugioniformis, include differences in fruit structure that influence their dispersal ability and within population spatial structure. Here, we tested within- and among-populations genetic variation, hypothesizing that (i) short-distance dispersal of heavy fruits in R. pugioniformis provided opportunities for local adaptions, while (ii) long-distances of single-seeded diaspores increase migration rates in R. raphanistrum, resulting in closer genetic distances among populations.

Methods: Populations were mapped along a geographical gradient in the eastern Mediterranean, and genotyping-by-sequencing (GBS) was employed to assess population genetic structure. Population genetic variation was analyzed using genetic diversity parameters, pairwise genetic differentiation coefficients, Mantel tests, migration rates (MR), and ADMIXTURE analyses. Furthermore, SNP detection was utilized to identify loci associated with local adaptations.

Key results: The average values of migration rates were similar in the two species, and non-synonymous SNP loci in CDS regions of R. raphanistrum (n=12) and R. pugioniformis (n=7) were well associated with directional selection. However, the genetic diversity parameters, isolation-by-distance Mantel tests, PCoA, and ADMIXTURE analyses indicated higher genetic differentiation among populations of R. pugioniformis than among populations of R. raphanistrum. Furthermore, a higher number of loci in R. pugioniformis than in R. raphanistrum (12 vs. 3 SNP outlier loci, respectively) were associated with average annual rainfall, the most prominent environmental parameter in the east Mediterranean.

Conclusions: The results support the hypothesis that long-distance dispersal contributes to lower genetic diversity in populations of R. raphanistrum compared to R. pugioniformis. Considering that the distribution range of R. raphanistrum is relatively homogenous, whereas R. pugioniformis is scattered across varying topographical and climatic gradients, the results of this genome scan highlight the significant role of the environment in adaptive inter- and intra-species genetic variation in these two genetically-close species.