Academic literature on the topic 'Basal angiosperms'

Abstract Background and Aims Our aim was to understand the environmental conditions of the emergence and radiation of early angiosperms. Such a question has long remained controversial because various approaches applied in the past have drawn conflicting images of early angiosperm ecology. Methods We provided a new perspective on the question by using support vector machines to model the environmental niche of 51 species belonging to ten genera of extant lineages that diverged early during angiosperm evolution (basal angiosperms). Then, we analysed the resulting pattern of niche overlap and determined whether this pattern deviates from what would be expected on the basis of a null model or whether it might mirror a legacy of a common primitive niche based on a phylogenetic reconstruction. Key Results The niche of three-quarters of the species and all genera converged towards tropical montane cloud forests (TMCFs). The latitudinal pattern of basal angiosperm richness indeed culminated in the tropics, and the elevational pattern revealed a humpback curve peaking between 2000 m and 3500 m when accounting for the effect of area. At first glance, this diversity pattern does not significantly differ from null predictions. However, we revealed a tendency for the basal-most taxa to occur in TMCFs so that phylogenetic reconstructions indicated that the niche of the common ancestor of the sampled basal angiosperms had a probability of 0.85–0.93 to overlap with TMCFs. Conclusions Our new approach indicates that the environmental convergence of extant basal angiosperms towards TMCFs would reflect a legacy of an ancestral niche from which the least basal taxa would have diverged following a random pattern under geometric constraints.

The photosynthetic gas exchange capacities of early angiosperms remain enigmatic. Nevertheless, many hypotheses about the causes of early angiosperm success and how angiosperms influenced Mesozoic ecosystem function hinge on understanding the maximum capacity for early angiosperm metabolism. We applied structure-functional analyses of leaf veins and stomatal pore geometry to determine the hydraulic and diffusive gas exchange capacities of Early Cretaceous fossil leaves. All of the late Aptian—early Albian angiosperms measured possessed low vein density and low maximal stomatal pore area, indicating low leaf gas exchange capacities in comparison to modern ecologically dominant angiosperms. Gas exchange capacities for Early Cretaceous angiosperms were equivalent or lower than ferns and gymnosperms. Fossil leaf taxa from Aptian to Paleocene sediments previously identified as putative stem-lineages to Austrobaileyales and Chloranthales had the same gas exchange capacities and possibly leaf water relations of their living relatives. Our results provide fossil evidence for the hypothesis that high leaf gas exchange capacity is a derived feature of later angiosperm evolution. In addition, the leaf gas exchange functions of austrobaileyoid and chloranthoid fossils support the hypothesis that comparative research on the biology of living basal angiosperm lineages reveals genuine signals of Early Cretaceous angiosperm ecophysiology.

Despite more than a century of research, some key aspects of habitat preference and ecology of the earliest angiosperms remain poorly constrained. Proposed growth ecology has varied from opportunistic weedy species growing in full sun to slow-growing species limited to the shaded understorey of gymnosperm forests. Evidence suggests that the earliest angiosperms possessed low transpiration rates: gas exchange rates for extant basal angiosperms are low, as are the reconstructed gas exchange rates for the oldest known angiosperm leaf fossils. Leaves with low transpirational capacity are vulnerable to overheating in full sun, favouring the hypothesis that early angiosperms were limited to the shaded understorey. Here, modelled leaf temperatures are used to examine the thermal tolerance of some of the earliest angiosperms. Our results indicate that small leaf size could have mitigated the low transpirational cooling capacity of many early angiosperms, enabling many species to survive in full sun. We propose that during the earliest phases of the angiosperm leaf record, angiosperms may not have been limited to the understorey, and that some species were able to compete with ferns and gymnosperms in both shaded and sunny habitats, especially in the absence of competition from more rapidly growing and transpiring advanced lineages of angiosperms.

Abstract Amborella trichopoda is placed close to the base of the angiosperm lineage (basal angiosperm). By genome-wide RNA sequencing, we identified 184C-to-U RNA editing sites in the plastid genome of Amborella. This number is much higher than that observed in other angiosperms including maize (44 sites), rice (39 sites) and grape (115 sites). Despite the high frequency of RNA editing, the biased distribution of RNA editing sites in the genome, target codon preference and nucleotide preference adjacent to the edited cytidine are similar to that in other angiosperms, suggesting a common editing machinery. Consistent with this idea, the Amborella nuclear genome encodes 2–3 times more of the E- and DYW-subclass members of pentatricopeptide repeat proteins responsible for RNA editing site recognition in plant organelles. Among 165 editing sites in plastid protein coding sequences in Amborella, 100 sites were conserved at least in one out of 38 species selected to represent key branching points of the angiosperm phylogenetic tree. We assume these 100 sites represent at least a subset of the sites in the plastid editotype of ancestral angiosperms. We then mapped the loss and gain of editing sites on the phylogenetic tree of angiosperms. Our results support the idea that the evolution of angiosperms has led to the loss of RNA editing sites in plastids.

A review of the present perspective of basal angiosperms and the steps that led to this perspective is provided. Major steps of progress over the past century can be seen with the discovery of new extant plants (Degeneria), new fossils and the advent of new research methods, especially molecular cladistic studies, which catalysed new waves of research. A spectacular result in 1999 was the identification of the well-supported basalmost clades of the angiosperms, forming the ANITA grade, with Amborella, Nymphaeales and Austrobaileyales, by several research groups. This provided a new framework in which basal angiosperms can be discussed in evolutionary terms. In this review basalmost angiosperms (ANITA grade and Chloranthaceae) and other basal angiosperms (eumagnoliids and Ceratophyllaceae) are addressed, with a focus on the different major clades and on general traits and evolutionary tendencies. A short outlook for future avenues is also provided.

The Lepidoptera represent one of the most successful radiations of plant-feeding insects, which predominantly took place within angiosperms beginning in the Cretaceous period. Angiosperm colonization is thought to underlie the evolutionary success of the Lepidoptera because angiosperms provide an enormous range of niches for ecological speciation to take place. By contrast, the basal lepidopteran lineage, Micropterigidae, remained unassociated with angiosperms since Jurassic times but nevertheless achieved a modest diversity in the Japanese Archipelago. We explored the causes and processes of diversification of the Japanese micropterigid moths by performing molecular phylogenetic analysis and extensive ecological surveying. Phylogenetic analysis recovered a monophyletic group of approximately 25 East Asian endemic species that feed exclusively on the liverwort Conocephalum conicum , suggesting that niche shifts hardly played a role in their diversification. Consistent with the low flying ability of micropterigid moths, the distributions of the Conocephalum specialists are each localized and allopatric, indicating that speciation by geographical isolation has been the major process shaping the diversity of Japanese Micropterigidae. To our knowledge, this is the largest radiation of herbivorous insects that does not accompany any apparent niche differentiation. We suggest that the significance of non-ecological speciation during the diversification of the Lepidoptera is commonly underestimated.

En raison de sa remarquable diversité végétale, de son taux d’endémisme, parmi les plus élevés au niveau mondial (79%) et de son extrême vulnérabilité, la Nouvelle-Calédonie est un des premiers hotspots de la biodiversité mondiale. L’une des remarquables originalités de la flore Calédonienne repose sur la présence de nombreux taxa reconnus, en raison de leurs positions phylogénétiques, comme appartenant aux lignées les plus anciennes des plantes à fleurs. Ces lignées d’Angiospermes « reliques » ont une valeur scientifique et patrimoniale importante, puisqu’elles sont de véritables fenêtres sur le passé. A travers l’étude des traits foliaires, de l’anatomie du bois (e.g. type d’éléments conducteurs, perforations, diamètre et longueur des vaisseaux), de l’architecture (e.g. sympoldialité vs monopodialité, phénomène de réitération, rythmicité de croissance) et de la biomécanique des axes, nous chercherons à caractériser les formes et fonctions de ces taxons. Ce projet de thèse vise à examiner les déterminants structurels et fonctionnels de la répartition spatiale actuelle des Angiospermes basales (grade ANITA + Magnoliidae) en Nouvelle-Calédonie. Dans cette perspective nous chercherons à comprendre quels sont les facteurs qui ont conduit au confinement de certains taxons à des habitats restreints ou au contraire à leur dispersion dans des milieux contrastés. Un premier volet du projet en cours, a pour objectif de caractériser la dynamique de croissance d’Amborella trichopoda et sa plasticité architecturale sous différents régimes lumineux. Certains traits écologiques de ces espèces d’Angiospermes de divergence précoce, s’ils n’ont pas contribué à la radiation des plantes à fleurs actuelles, ont pu permettre son enracinement écologique au sein de la flore du Mésozoïque et fournir un répertoire développemental pour l’explosion subséquente de leur diversité. L’identification et l’étude de ces caractères sont donc déterminantes pour la compréhension de l’évolution structurelle et fonctionnelle des plantes à fleurs<br>New Caledonia (NC) is one of the main biodiversity hotspots (Myers 1988), this is because of its remarkable plant diversity, its endemism rates, among the highest in the world (79%), and because of the vulnerability of its flora. One of the main originalities of New Caledonia flora is based on the presence of a large number of taxa recognized, due to their phylogenetical positions, as the most ancient extant representatives of angiosperms. For a long time, New Caledonia has been considered as an early upset fragment of the Gondwana (Pelletier 2006) that suffered an interrupted history of isolation which conferred the evolutionary particularities that we observe today. However, recent evidences show that NC has derived from the Australian land during the late Mesozoic (~80 Mya), the island was then submerged during the first half of the Cenozoic (Pelletier 2006) and a reemergence of the island seems to have occurred ~37 Mya (Cluzel et al. 1998). After the reappearance of the island above the sea level, several events of recolonisation occurred and they wrought the biodiversity that we observe nowadays (Pillon 2012). NC presents humid forests which are unique relics; under the influence of climate changes, these forests have virtually disappeared from other regions of the globe (Morat et al. 1986). The lineages of “relictual” angiosperms, mainly subservient to these humid forests, have a great scientific and patrimony value, as they can be considered as genuine windows on the past. These taxa are susceptible to contain primitive characters which have either disappeared in most of the existing flowering plants, or that are still shared by a narrow number of them. The identification and the study of these characters are therefore determinants for the comprehension of angiosperms evolution. Some ecological features of these panchronic species, may have either contributed to the huge radiation of extant angiosperms, or they may have contributed to the ecological settling of angiosperms within the Mesozoic flora, providing them with a developmental repertoire for the subsequent explosion of their diversity. This PhD project aims to study the ecological, anatomical and functional diversity of basal angiosperms and it seeks to analyze the evolutionary patterns of these structural and functional features. We will consider here as “basal” angiosperms a great group of flowering plants that has diverged before the monocot and eudicot node. This group is conformed by the ANITA grade, formed by Amborella (a single species endemic to NC), Nymphaeales (waterlilies and other herbaceous aquatic plants) and Austrobaileyales (aromatic woody plants). The Magnoliid subclass, a clade of flowering of early divergence, which contains plants considered as paleodicots by Cronquist (1988), will be also included in the analysis of the « basal » taxa. More recently, the Magnoliids have been redefined as a clade comprising Chloranthales, Canellales, Laurales, Magnoliales, et Piperales (APG III, 2009). In a second part of the project, a fieldtrip to Mexico will be held in order to include speces belonging to the Chloranthaceae and Schisandraceae, as well as Cabombaceae et Nymphaeaceae, by this means, we will incorporate species belonging to all the orders of the “basal” angiosperms, reinforcing the comparative analysis. This research work will lean on the recent publications of the phylogenetic relations within basal angiosperms

The Aristolochiaceae are one of the largest angiosperm families, the family has been divided into two subfamilies: Asaroideae, which include Asarum and Saruma, and Aristolochioideae, which includes Thottea sensu lato and Aristolochia sensu lato (Kelly and Gonzales, 2003). Aristolochia sensu lato comprise between 450 and 600 species, distributed throughout the world with centers of diversities in the tropical and subtropical regions (Neinhuis et al., 2005, Wanke et al., 2006a, 2007). However, the extended Mediterranean region including Turkey, the Caucasus and the Near East is likely to be the only diversity hotspot of the genus Aristolochia in the northern hemisphere were up to 60 species and subspecies could be observed (Wanke 2007). Most important contributions to the knowledge of these species were published by Nardi (1984, 1988, 1991, 1993) and Davis &amp; Khan (1961, 1964, 1982), all of these studies were based on morphological characters only. In recent years, with the progress of molecular techniques and in light of the systematic chaos, a detailed study was needed to unravel the evolutionary history prior to a taxonomic revision of this group. The first chapter of my thesis should be regarded as the starting point for more detailed investigation on population level. Preliminary molecular phylogenitic analysis recovered the Mediterranean Aristolochia species as monophyletic (de Groot et al 2006). However, only very few members were included in that study. The latest phylogenetic study by Wanke (2007) dealed with west Mediterranean Aristolochia species and sampled also few members belonging to the east Mediterranean and Caucasian species (3 from Greece, 2 from Georgia and 1 from Turkey). This study reported the Mediterranean Aristolochia species as two molecular and morphologically well supported clades, which were sister to each other. Furthermore, the two closely related species A. sempervirens and A. baetica which have an east west vicariance and are known as Aristolochia sempervirens complex has been recovered as sister group to the remaining west Mediterranean species. A detailed investigation of the evolutionary history of this group is the topic of the second chapter of my thesis (Chapter 2). The Aristolochia sempervirens complex is characterized by an unusual growth form and has a circum Mediterranean distribution. The investigation of these species complex seem to be of great importance to understand speciation and colonization of the Mediterranean by the genus Aristolochia and might shade light in historical evolutionary processes of other plant lineages in the Mediterranean. Furthermore, I test applicability and phylogenetic power of a nuclear single copy gene (nSCG) region to reconstruct well resolved and highly supported gene genealogies as a prerequisite to study evolutionary biology questions in general. Furthermore, a comprehensive overview of leaf epicuticular waxes, hairs and trichomes of 54 species from the old and new world taxa of the genus Aristolochia were investigated using scanning electron microscopy (SEM) to clarify taxonomic status of theses species in contrast to their molecular position. Also this study which is the third chapter of this thesis (Chapter 3), has a strong focus on Mediterranean Aristolochia and tries to provide additional support for molecular findings based on epicuticular waxes and to test them as synapomorphies. Each chapter has its own introduction and abstract resulting in a short general introduction here.

The first half of the thesis deals with the seed morphology of members of the ANITA grade at the base of the angiosperm phylogeny (Amborella, Nymphaeales, Illiciales, Trimeniaceae, and Austrobaileyaceae), especially Illiciaceae and Schisandraceae. Seed characters support a major division between the New World and Old World species of Illicium. Fossil seeds previously assigned to Illiciaceae were re-evaluated. In Schisandraceae, seed and leaf epidermal characters were added to a previously published morphological data matrix. Phylogenetic analysis using the extended data matrix shows that Kadsura and Schisandra appear to be supported as monophyletic sister taxa by a number of synapomorphies in reproductive and vegetative characters. Fossil seeds from the Eocene of North America show some similarities to the modern Schisandra glabra from North America, whereas fossils from Europe are more similar to modern Asian species. In the second half of the thesis, seed morphology of Lysimachia and closely related taxa (Anagallis, Ardisiandra, Asterolinon, Glaux, Pelletiera, Trientalis) was investigated. The phylogenetic relationships among the endemic Hawaiian species of Lysimachia was also studied, using nuclear ribosomal DNA (ETS, ITS) and chloroplast DNA (rpl16, rpl20-rps12, rps16, trnH-psbA, trnS-G) sequence data. The seeds in Lysimachia and related taxa vary in, e.g., shape, seed coat structure and surface patterns. Seed surface patterns are mostly congruent with molecular phylogenetic relationships. A reticulate surface pattern is diagnostic for, e.g., the subgenus Palladia and the Hawaiian endemic subgenus Lysimachiopsis. Mapping seed characters onto a recent molecular-based phylogenetic tree, reveals that they provide potentially synapomorphic character states for various subclades of Lysimachia. The phylogenetic analysis based on the combined data set using nuclear ribosomal DNA and chloroplast DNA data provides new insights into the relationships within the Hawaiian subgenus Lysimachiopsis. Here our results indicate that earlier taxonomic treatments of the group need to be partially revised.

Avocado is an economically important crop with ~ 60-70 % oil, by dry weight, in its fruit mesocarp tissue. The steady increase in global demand for avocado (9% per year) has driven interest to identify the biochemical and molecular factors that regulate its triacylglycerol (TAG, oil) biosynthesis. Using 454- and Illumina-based RNA-Seq approaches, we examined the transcriptional basis for TAG biosynthesis in developing mesocarp of avocado, in relation to other seed and non-seed tissues. Deep transcriptional profiling data allowed us to identify several transcripts that were differentially represented between the early and late developmental stages of mesocarp. Additionally, in all oil-rich tissues analyzed, irrespective of the species, an increased expression was noted for genes mostly associated with fatty acid biosynthesis in plastid, but much less increase in those for TAG assembly in the endoplasmic reticulum. Transcripts associated with hexose metabolism in plastid also showed higher expression, relative to cytosol; this is likely associated with the need for high pyruvate flux directed toward plastid fatty acid synthesis. Moreover, WRINKLED1 transcription factor, a regulatory element associated with oil biosynthesis in seed and non-seed tissues of monocot and dicot plants, was identified in avocado as well. Our studies point to distinctive modes of regulation of fatty acid biosynthesis and TAG assembly that are conserved in both seed and non-seed oil-rich plants. In addition to improving avocado oil production, our study will lead to understanding regulation of oil biosynthesis in coordination with fruit development and identification of ways to generate oil-rich bioenergy crops; a direct implication for the science & society. This study provides an evolutionary insight into conserved nature of oil biosynthesis in a basal angiosperm (avocado) in relation to a monocot (oil palm) and a dicot (brassica). This research will lead to publications for students, sustain existing collaborations (Israel, CA, FL avocado researchers) and generate external funds.

The mechanism by which plants synthesize and store high amounts of triacylglycerols (TAG) in tissues other than seeds is not well understood. The comprehension of controls for carbon partitioning and oil accumulation in nonseed tissues is essential to generate oil-rich biomass in perennial bioenergy crops. Persea americana (avocado), a basal angiosperm with unique features that are ancestral to most flowering plants, stores ~ 70 % TAG per dry weight in its mesocarp, a nonseed tissue. Transcriptome analyses of select pathways, from generation of pyruvate and leading up to TAG accumulation, in mesocarp tissues of avocado was conducted and compared with that of oil-rich monocot (oil palm) and dicot (rapeseed and castor) tissues to identify tissue- and species-specific regulation and biosynthesis of TAG in plants.