Brenda Hernandez-HernandezRosalinda Tapia-LopezBarbara A. AmbroseAlejandra Vasco...
1-8页
查看更多>>摘要：Premise of research. MYB transcription factors are one of the largest families of genes in land plants. They are involved in many regulatory processes, such as primary and secondary metabolism, cell fate and identity, developmental processes, and responses to biotic and abiotic stresses. Phylogenetic studies have mainly focused on R2R3-MYB evolution in seed plants; however, a comprehensive sampling across land plants is lacking, as none have included ferns. Methodology. To better understand the evolution of R2R3-MYB genes in land plants, we surveyed the R2R3-MYB gene sequences from six genomes belonging to the main lineages of land plants (bryophytes, lycophytes, ferns, angiosperms, and gymnosperms). In addition, we searched transcriptome sequences of selected fern and lycophyte transcriptomes. We assembled a nucleotide matrix of the MYB domain and conducted maximum likelihood analyses to infer phylogenetic relationships and gene-tree reconciliation analyses to infer gene duplications. We labeled the main clades with the known MYB functions onto the resulting tree. To detect reported as well as new conserved motifs, we ran protein motif analyses through MEME. Pivotal results. Our results support previous studies indicating that R2R3-MYBs in seed plants are more diverse than in any other lineage of vascular plants. Most of the well-supported clades recovered are inferred to be already present in the ancestor of land plants. We found that ferns have numerous copies of R2R3-MYBs, although not as many as seed plants. Protein motif analyses revealed that R2R3-MYB motifs are highly conserved across land plants, suggesting that most R2R3-MYB orthologues, including those of ferns, might have DNA-binding capabilities and could be involved in regulatory processes that are similar to those of their angiosperm homologues. Our analyses showed that there are no fern orthologues of the angiosperm MYB leaf developmental genes ARP, raising interesting questions about the evolution and origin of leaves in ferns and seed plants. Conclusions. Our results provide the phylogenetic context for research on the genetic and functional evolution of an important gene family of developmental and metabolic regulators across the plant tree of life.
查看更多>>摘要：Premise of research. Serotiny is a specialized dispersal mechanism in which seeds are retained on the parent plant and released following a disturbance event. This strategy has evolved repeatedly in plants inhabiting fire-prone regions and typically requires adaptations for the protection and release of seeds. We explore the relationship between serotiny and reproductive morphology in the Cupressaceae conifer clade, asking whether serotiny is associated with the evolution of larger, more protective seed cones. Methodology. We compiled cone volume data from 72 extant Cupressaceae species, with detailed cone and seed mass measurements from 19. Using phylogenetic regressions and a previously published phylogeny, we reconstructed how many times serotiny evolved in Cupressaceae and asked whether its appearance was correlated with larger seed cones. We also tested whether cones from serotinous taxa produced proportionally more sterile tissues than those from nonserotinous taxa. Pivotal results. Serotiny has likely evolved five times within extant Cupressaceae, and each time it is correlated with the evolution of larger seed cones. The larger cones of serotinous taxa do not show proportionally more investment in sterile tissues, however. Conclusions. The relationship between cone size and serotiny is particularly strong in Cupressaceae because their branching architecture favors the production of small cones; fire regimes can then exert a strong selective pressure favoring larger ones. Conifers that produce generally larger seed cones may be less likely to show a correlation with serotiny. Considering seed cone size and branching architecture together, however, may allow for the interpretation of serotiny in the conifer fossil record.
查看更多>>摘要：Premise of research. A two-phase fern spike occurred immediately after the Cretaceous-Paleogene (K/Pg) mass extinction event. Solely on the basis of palynological evidence, researchers have traditionally attributed the first phase of this spike to the proliferation of a single species of a Cyathea-like fern in the earliest Danian. This traditional perspective is challenged by recent investigations linking Anemia-like fern foliage with Cyathidites spores at K/Pg boundary localities in the Raton Basin, where the fern spore spike was first discovered by R. H. Tschudy. Although evidence emerging from neighboring basins appears to corroborate this new perspective, it remains to be seen whether this generalization applies to the northern Great Plains. Methodology. A comprehensive list of the most common fern megafossils collected from earliest Danian plant localities across western North America was compiled to determine the number and potential identity of Cyathidites-producing ferns. Pivotal results. Three K/Pg survivors commonly collected from basal Paleocene strata in western North America conceivably produced psilate, trilete (Cyathidites) fern spores essentially identical to those observed at the K/Pg boundary fern spore spike: Anemia elongata (Newberry) Knowlton, Dennastra sorimarginata Mclver et Basinger, and the Coniopteris-like fern "Dennstaedtia" americana Knowlton. Conclusions. Arborescent ferns were not among the first plants in western North America to thrive in the immediate wake of ecological collapse at the K/Pg boundary. Basal polypod ferns can be linked to Cyathidites spores in the northern Great Plains, perhaps because of a latitudinal climatic gradient. These results could explain taxonomic inversion in the dual-phase fern spore spike between western North America and New Zealand.
Else Marie FriisPeter R. CraneKaj Raunsgaard Pedersen
28-45页
查看更多>>摘要：Premise of research. Early Cretaceous flowers recovered from Portugal and North America are some of the oldest and most informative angiosperm structures known. Analyses of this material provide a more direct basis for inferring floral structure and biology in early angiosperms than extrapolations based solely on extant taxa, and they have documented an unanticipated diversity of angiosperms, including the presence of many extinct forms, during the Early Cretaceous. The fossil flower described here from the Early Cretaceous of Portugal adds to the knowledge of this extinct diversity. Methodology. Coalified fossil flowers were extracted from unconsolidated sediments and cleaned with HF, HCl, and water. Details were studied using scanning electron microscopy and synchrotron radiation X-ray to-mographic microscopy. Phylogenetic relationships were evaluated by adding the fossil to a phylogenetic analysis of extant basal angiosperms based on morphological characters but constrained according to a topology based on molecular data. Pivotal results. A new genus and species, Catanthus dolichostemon, are described on the basis of the fossil flowers. The perianth consists of three thick sepal-like tepals in an outer whorl and six thinner petallike tepals in two inner whorls. The androecium consists of several whorls of stamens with long, broad filaments and anthers with extrorse dehiscence. Pollen is trichotomocolpate and possibly monocolpate. The gynoecium is superior and apocarpous, consisting of six or, rarely, five carpels. Analysis of the phylogenetic position of Catanthus suggests a relationship to Canellales and Magnoliales. Conclusions. Catanthus is a new Early Cretaceous magnoliid angiosperm for which the relationship to the two major clades of extant magnoliids (Laurales + Magnoliales or Canellales + Piperales) is not resolved securely. Catanthus adds to the evidence of substantial extinct diversity among early angiosperms, including the presence of extinct forms related to extant magnoliids, and it is consistent with a general pattern that angiosperm assemblages from the middle Albian and earlier are dominated by noneudicots.
查看更多>>摘要：Premise of research. Metrosideros polymorpha is a landscape-dominant tree species endemic to the Hawaiian Islands. Although the group is famous for its ecological amplitude and variation in vegetative characters, little attention has been paid to variation in its "shaving brush" flowers, which occur in inflorescences of diverse sizes and colors. We aimed to determine whether the floral variation observed in natural populations is heritable and how this variation is distributed across environments and varieties of the species. Methodology. We measured seven floral traits in 93 adult trees representing three varieties of M. polymorpha in a common garden on the island of Hawaii and examined variation in these traits across elevations (of the source population) and varieties. Pivotal results. Flower length increased with elevation, while flower width decreased with elevation. Nectar cup diameter and stamen length did not vary across elevations. Variation in flower color decreased with increasing elevation, with only dark red-flowered trees observed from the two highest elevations. Much of the variation observed in floral traits was partitioned among the three varieties in the garden. Stigma-anther separation (SAS) was significantly lower in var. incana, while long flowers and smaller inflorescences characterized var. polymorpha; var. glaberrima had the least distinct flowers. Conclusions. We observed a distinct floral morphology in the high-elevation var. polymorpha consistent with pollination predominantly by birds. The lower SAS observed in var. incana may be consistent with weaker selection against self-pollination in low-density populations of this early-successional variety on new lava flows. These results indicate that, in addition to divergence in vegetative traits associated with adaptation to contrasting abiotic conditions, varieties of M. polymorpha on the island of Hawaii show heritable differences in floral characters that may be associated with biotic factors.
查看更多>>摘要：Premise of research. Floral synorganization is a structural feature of many speciose angiosperm taxa and is considered a morphological innovation paving the way for evolutionary diversification. Staphisagria is sister to the remaining Delphinieae, the only lineage of Ranunculaceae characterized by zygomorphic flowers. We aim at providing a description of floral organogenesis and morphogenesis in both Staphisagria species, presenting the disparity of Delphinieae hyperorgans in a phylogenetic framework, and proposing a scenario of likely developmental pathways underlying the different types of hyperorgans in Delphinieae. Methodology. We carried out morphological, anatomical, and developmental studies on flowers of S. macro-sperma and S. picta. Pivotal results. Synorganization is complex in Staphisagria and Delphinieae as a whole and involves flower dorsoventralization, the nesting of spurs, the postgenital fusion of petals, and the formation of a shared cavity. From a choripetalous ancestor, late and partial postgenital fusion among dorsal petals evolved once or twice in the tribe. Conclusions. The Delphinieae flower includes nested spurs and nested floral parlors. These key innovations, unique in angiosperms, probably led to the diversification of this species-rich tribe in the Northern Hemisphere. The lengths of the inner (nectariferous) spurs and the nested floral parlors determine the range of pollinators able to collect nectar. These traits could be used to revise the circumscription of taxonomic groups within the tribe and should be taken into account when examining the possible coevolution between Delphinieae flowers and their pollinators. Integrating this new knowledge about the hyperorgan will be essential for future research in taxonomy, evo-devo, and pollination ecology in Delphinieae.
Arthur Domingos-MeloUgo Mendes DinizSofia Lucas ChalegreIsabel Cristina Machado...
71-77页
查看更多>>摘要：Premise of research. Bat-pollinated flowers have wide morphologies and produce copious and diluted nectar that commonly spills from flowers. Considering that sugar concentration modulates rheological properties in aqueous solutions, we estimated its role in regulating nectar retention. Methodology. We took three bat-pollinated species with open floral morphologies (Calliandra aeschynome-noides; Hymenaea cangaceira, Fabaceae; and Tarenaya longicarpa, Cleomaceae) as models. We evaluated how sugar concentration affects their nectar retention through experiments with artificial nectar in different sugar percentages. We also reported the volume and concentration of sugar in the nectar drops of these flowers under natural conditions. Pivotal results. Depending on the plant species, higher sugar concentration can improve nectar retention, reduce it, or even present intermediate values that enable the retention of larger nectar volumes. Nevertheless, sugar concentrations from flowers in the field do not coincide with those that allow a greater accumulation of nectar, and flowers retain smaller volumes than recorded in experiments. Conclusions. Peculiarities of each flower (e.g., size, thickness, and quantities of structures available for nectar adhesion) ensure distinct effects from sugar concentration on nectar retention. Even so, it seems that there is no strategy from plants to prevent spillage of nectar by regulating the sugar concentration. Shifts in the sugar concentration of nectar may influence other aspects of the pollination biology of the species. Spilling part of the produced nectar, despite seeming to be a paradoxical waste of resources, can be a less impactful factor.
NETL
NSTL
Univ Chicago Press