The somatic genomic landscape of glioblastoma.

We describe the landscape of somatic genomic alterations based on multidimensional and comprehensive characterization of more than 500 glioblastoma tumors (GBMs). We identify several novel mutated genes as well as complex rearrangements of signature receptors, including EGFR and PDGFRA. TERT promoter mutations are shown to correlate with elevated mRNA expression, supporting a role in telomerase reactivation. Correlative analyses confirm that the survival advantage of the proneural subtype is conferred by the G-CIMP phenotype, and MGMT DNA methylation may be a predictive biomarker for treatment response only in classical subtype GBM. Integrative analysis of genomic and proteomic profiles challenges the notion of therapeutic inhibition of a pathway as an alternative to inhibition of the target itself. These data will facilitate the discovery of therapeutic and diagnostic target candidates, the validation of research and clinical observations and the generation of unanticipated hypotheses that can advance our molecular understanding of this lethal cancer.

A bump in the node: The hydraulic implications of rhizomatous growth.

PREMISE: Rhizomatous growth characterizes numerous taxa among vascular plants. While abundant information exists on nutrient sharing and demography, the question of how these metameric organisms move water through their bodies remains largely unstudied. Moreover, we lack an understanding of the evolutionary implications of rhizomatous growth across vascular plants. Here, we examined these questions by investigating how rhizomatous growth and vascular construction affect whole-plant hydraulic function. METHODS: In five terrestrial fern species with diverse vascular construction, we used microcomputed tomography and bright-field microscopy to examine vascular construction across nodes along the rhizome. These data were integrated with measurements of leaf stomatal conductance under rooted and uprooted conditions to relate vascular patterning and hydraulic architecture to leaf water status. RESULTS: Similar to phytomers of woody seed plants, nodal regions in rhizomatous ferns are areas of hydraulic resistance. While water is shared along the rhizomes of these investigated species, hydraulic conductivity drops at nodes and stomatal conductance declines when nodes were locally uprooted. Together, our data suggest that nodes are chokepoints in axial water movement along the rhizome. CONCLUSIONS: Nodal chokepoints decrease hydraulic integration between phytomers. At the same time, chokepoints may act as "safety valves", hydraulically localizing each phytomer-potentially decreasing embolism and pathogen spread. This suggests a potential trade-off in the principal construction of the fern rhizome. Moreover, we propose that shoot-borne roots (homorhizy) and the prostrate habit of rhizomatous ferns decrease the hydraulic and structural burdens that upright plants typically incur. The absence of these hydraulic and structural demands may be one reason ferns (and many rhizomatous plants) lack, or have minimally developed, secondary xylem.

Water lily (Nymphaea thermarum) genome reveals variable genomic signatures of ancient vascular cambium losses.

For more than 225 million y, all seed plants were woody trees, shrubs, or vines. Shortly after the origin of angiosperms ∼140 million y ago (MYA), the Nymphaeales (water lilies) became one of the first lineages to deviate from their ancestral, woody habit by losing the vascular cambium, the meristematic population of cells that produces secondary xylem (wood) and phloem. Many of the genes and gene families that regulate differentiation of secondary tissues also regulate the differentiation of primary xylem and phloem, which are produced by apical meristems and retained in nearly all seed plants. Here, we sequenced and assembled a draft genome of the water lily Nymphaea thermarum, an emerging system for the study of early flowering plant evolution, and compared it to genomes from other cambium-bearing and cambium-less lineages (e.g., monocots and Nelumbo). This revealed lineage-specific patterns of gene loss and divergence. Nymphaea is characterized by a significant contraction of the HD-ZIP III transcription factors, specifically loss of REVOLUTA, which influences cambial activity in other angiosperms. We also found the Nymphaea and monocot copies of cambium-associated CLE signaling peptides display unique substitutions at otherwise highly conserved amino acids. Nelumbo displays no obvious divergence in cambium-associated genes. The divergent genomic signatures of convergent loss of vascular cambium reveals that even pleiotropic genes can exhibit unique divergence patterns in association with independent events of trait loss. Our results shed light on the evolution of herbaceousness-one of the key biological innovations associated with the earliest phases of angiosperm evolution.

Rapid diversification of vascular architecture underlies the Carboniferous fern radiation.

Vascular plants account for 93% of Earth's terrestrial flora. Xylem and phloem, vital for transporting water and nutrients through the plant, unite this diverse clade. Three-dimensional arrangements of these tissues (vascular architecture) are manifold across living and extinct species. However, the evolutionary processes underlying this variation remain elusive. Using ferns, a diverse clade with multiple radiations over their ca 400-million-year history, we synthesized data across 3339 species to explore the tempo and mode of vascular evolution and to contextualize dynamics of phenotypic innovation during major fern diversification events. Our results reveal three paradigm shifts in our understanding of fern vascular evolution. (i) The canonical theory on the stepwise and unidirectional evolution of vascular architecture does not capture the complexities of character evolution among ferns. Rather, a new model permitting additional transitions, rate heterogeneity and multiple reversions is more likely. (ii) Major shifts in vascular architecture correspond to developmental changes in body size, not regional water availability. (iii) The early Carboniferous radiation of crown-group ferns was characterized by an explosion of phenotypic innovation. By contrast, during the Cretaceous and Cenozoic rise of eupolypods, rates of vascular evolution were dramatically low and seemingly decoupled from lineage diversification.

Interspecific morphological variation in Juglandoideae resting bud organization: a winter's tale?

BACKGROUND AND AIMS: Dormant resting buds are frequently regarded as static units, with protective cataphylls on the outside and embryonic foliage leaves on the inside. How the presence of cataphylls influences the dynamic, cyclical, annually repeating sequence of leaf forms that a resting bud gives rise to has rarely been interrogated. To examine the connection between dormant structure and growing-season development, we compare the complete seasonal heteroblastic sequence of leaf forms of six species of temperate Juglandaceae with distinctly different vegetative resting bud structures. These include buds with cataphylls; buds without cataphylls; and buds with caducous cataphylls that are lost before the onset of winter. METHODS: In a common garden setting over a 7-month growing season, the dimensions of 2249 individual vegetative metamers were tracked from first exposure to abscission along the shoots of saplings and mature trees. The timing of metamer initiation within terminal buds was investigated using micro-CT scanning. Character state transitions of resting bud types were estimated using a phylogenetic tree of Juglandaceae. KEY RESULTS: The presence of cataphylls within a heteroblastic sequence is associated with a single cohort of foliage leaves that flush and abscise synchronously. This growing pattern is highly determinate, with next year's terminal-bud cataphylls already initiated before spring leaf out. In contrast, in sequences without cataphylls, shorter-lived foliage leaves appear and abscise in a staggered fashion. Despite these differences in leaf demography, all examined heteroblastic sequences produce a series of small, caducous leaf forms that precede terminal bud set. CONCLUSIONS: The ubiquity of caducous leaf forms in Juglandoideae may point to the importance of shoot tip protection far beyond the dormant season. In addition, the presence or absence of cataphylls in resting buds is indicative of distinct shoot ontogenetic patterns, and functional strategies, in summer.

Repeat single-fraction stereotactic radiosurgery for recurrent vestibular schwannoma.

Background: Data are scarce on the efficacy of a second radiosurgery (SRS) treatment of vestibular schwannoma that has progressed following initial treatment with SRS. We sought to report the outcome of our repeat SRS series with long-term imaging follow-up. Materials and methods: We retrospectively analyzed 6 patients who met the following criteria: Repeat SRS at our institution between 1995 and 2018; solitary unilateral tumor; no evidence of neurofibromatosis; and magnetic resonance (MR) planning for both SRS treatments. All treatments were delivered with a linear accelerator-based system using head frame immobilization. The prescribed dose to the periphery of the tumor was 12.5 Gy in all initial and repeat SRS treatments, except for one repeat treatment to 10 Gy. Results: Follow-up with MR scan following the second SRS treatment was a median 8.4 years. The tumor control rate (lack of progression) following the second SRS treatment was 83% (5/6). Actuarial 10-year outcomes following repeat SRS were: tumor control, 80%; absolute survival, 80%; and cause-specific survival, 100%. Of the patients with at least minimal hearing retention before initial SRS, none had ipsilateral hearing preservation after initial radiation treatment. Improvement in any pretreatment cranial nerve deficits was not seen. The only permanent grade ≥ 3 toxicity from repeat SRS was a case of infraorbital nerve deficit. No patient developed a stroke, malignant transformation, induced second tumor, or facial nerve deficit. Conclusion: There was excellent overall survival, tumor control, and low morbidity in our series for recurrent vestibular schwannoma submitted to repeat single-fraction SRS, supporting additional studies of this treatment strategy.

From cells to stems: the effects of primary vascular construction on drought-induced embolism in fern rhizomes.

While a considerable amount of data exists on the link between xylem construction and hydraulic function, few studies have focused on resistance to drought-induced embolism of primary vasculature in herbaceous plants. Ferns rely entirely on primary xylem and display a remarkable diversity of vascular construction in their rhizomes, making them an ideal group in which to examine hydraulic structure-function relationships. New optical methods allowed us to measure vulnerability to embolism in rhizomes, which are notoriously difficult to work with. We investigated five fern species based on their diverse xylem traits at the cellular, histological, and architectural levels. To link below- and above-ground hydraulics, we then measured leaf-stem vulnerability segmentation. Overall, rhizome vulnerability to embolism was correlated most strongly with cellular but not histological or architectural traits. Interestingly, at P6-12 , species with increased architectural dissection were actually more vulnerable to embolism, suggesting different hydraulic dynamics at low compared to high percent embolism. Importantly, leaves fully embolize before stems reach P88 , suggesting strong vulnerability segmentation. This is the first study to explore the functional implications of primary vascular construction in fern rhizomes and leaf-stem vulnerability segmentation. Strong segmentation suggests that leaves protect perennial rhizomes against severe drought stress and hydraulically induced mortality.

Naked resting bud morphologies and their taxonomic and geographic distributions in temperate, woody floras.

Resting bud cataphylls are often assumed to play an essential protective role in winter due to their widespread presence among temperate, woody plants. This view is challenged by our documentation of significant numbers of temperate woody angiosperm taxa with naked buds that overwinter without cataphyll protection. We inventoried temperate, woody angiosperm taxa reported to have resting buds without cataphyll protection in winter and for the first time characterised the morphological and functional diversity of naked buds. Using this new classification of bud types, the taxonomic and geographic distributions of taxa with naked buds were summarised and relationships between plant functional traits and bud type were investigated. Naked buds are not, as long presumed, markedly rare in temperate, woody floras. They occur in at least 87 genera in 42 families throughout the angiosperm phylogeny in various morphologically distinct manifestations. The geographic distribution of species with naked buds in temperate areas was found to be associated with summer precipitation, but not with winter climatic variables. Resting bud structure is not necessarily a trait optimised solely for winter survival. A taxon's bud composition may be influenced by factors such as biogeographic history and ontogenetic pattern of leaf formation over the growing season.

Alexander Moritzi, a Swiss Pre-Darwinian Evolutionist: Insights into the Creationist-Transmutationist Debates of the 1830s and 1840s.

Alexander Moritzi (1806-1850) is one of the most obscure figures in the early history of evolutionary thought. Best known for authoring a flora of Switzerland, Moritzi also published Réflexions sur l'espèce en histoire naturelle (1842), a remarkable book about evolution with an overtly materialist viewpoint. In this work, Moritzi argues that the (then) generally accepted line between species and varieties is artificial, that varieties can over time give rise to new species, and that deep time and turnover of species in the fossil record clearly support an evolutionary interpretation of biological diversity. Moritzi was also a gradualist and viewed relationships between taxa as best represented by a ramifying tree. Although Réflexions was the first full book to be written on the topic of evolution following Lamarck's Philosophie zoologique (1809), Moritzi's evolutionist contribution was stillborn, read by almost no one in his lifetime and ultimately absent from the many historiographies of evolutionary thought. This is unfortunate since many of the arguments Moritzi marshaled on behalf of an evolutionary explanation of life can be found in subsequent transmutationist writings by Frédéric Gérard, Robert Chambers, Henri Lecoq, Baden Powell, Charles Naudin, Herbert Spencer, Alfred Russel Wallace, and Charles Darwin-none of whom is likely to have ever known of the existence of Réflexions. Finally, Moritzi's arguments, along with those found in Darwin's private essay on evolution of the same year, provide an excellent window into the state of evolutionary thought and debate over the nature of species at the beginning of the 1840s.

Evidence for parent-of-origin effects and interparental conflict in seeds of an ancient flowering plant lineage.

Theoretical and empirical studies have long connected the evolutionary innovation of endosperm, a genetically biparental product of a double fertilization process unique to flowering plants (angiosperms), to conflicting parental interests over offspring provisioning. Yet, none of these studies examined interparental conflict in representatives of any of the most ancient angiosperm lineages. We performed reciprocal interploidy crosses in the water lily Nymphaea thermarum, a member of one of the most ancient angiosperm lineages, Nymphaeales. We find that an excess of paternal genomes is associated with an increase in endosperm growth. By contrast, maternal ploidy negatively influences development or growth of all seed components, regardless of paternal genome dosage. Most relevant to the conflict over distribution of maternal resources, however, is that growth of the perisperm (seed storage tissue derived from the maternal sporophyte, found in all Nymphaeales) is unaffected by paternal genome dosage-ensuring maternal control of maternal resources. We conclude that the evolutionary transfer of embryo-nourishing function from a genetically biparental endosperm to a genetically maternal perisperm can be viewed as an effective maternal strategy to recapture control of resource distribution among progeny, and thus that interparental conflict has influenced the evolution of seed development in this ancient angiosperm lineage.

Prolonged embryogenesis in Austrobaileya scandens (Austrobaileyaceae): its ecological and evolutionary significance.

The embryology of basal angiosperm lineages (Amborella, Nymphaeales and Austrobaileyales) is central to reconstructing the early evolution of flowering plants. Previous studies have shown that mature seeds in Austrobaileyales are albuminous, with a small embryo surrounded by a substantial diploid endosperm. However, little is known of seed ontogeny and seedling germination in Austrobaileya scandens, sister to all other extant Austrobaileyales. Standard histochemical techniques were used to study ovule/seed development and germination of Austrobaileya. Early development of the endosperm in Austrobaileya is ab initio cellular with pronounced cell proliferation. The nucellus transiently accumulates some starch, but is obliterated by expansion of a massive endosperm, where all embryo-nourishing reserves are ultimately stored. Twelve months elapse from fertilization to fruit abscission. Seeds are dispersed with a minute embryo, requiring 12 additional months for seedling establishment. The 2 yr required for seedling establishment is an apomorphic feature of Austrobaileya, probably related to germination in extremely dark understory conditions. Remarkably, although Austrobaileya seeds are nearly 50 times larger (by length) than the smallest seeds of extinct and extant members of early divergent angiosperm lineages, the embryo to seed ratio (E : S) falls squarely within the narrow range that characterizes the albuminous seeds of ancient flowering plant lineages.

Insights from the pollination drop proteome and the ovule transcriptome of Cephalotaxus at the time of pollination drop production.

BACKGROUND AND AIMS: Many gymnosperms produce an ovular secretion, the pollination drop, during reproduction. The drops serve as a landing site for pollen, but also contain a suite of ions and organic compounds, including proteins, that suggests diverse roles for the drop during pollination. Proteins in the drops of species of Chamaecyparis, Juniperus, Taxus, Pseudotsuga, Ephedra and Welwitschia are thought to function in the conversion of sugars, defence against pathogens, and pollen growth and development. To better understand gymnosperm pollination biology, the pollination drop proteomes of pollination drops from two species of Cephalotaxus have been characterized and an ovular transcriptome for C. sinensis has been assembled. METHODS: Mass spectrometry was used to identify proteins in the pollination drops of Cephalotaxus sinensis and C. koreana RNA-sequencing (RNA-Seq) was employed to assemble a transcriptome and identify transcripts present in the ovules of C. sinensis at the time of pollination drop production. KEY RESULTS: About 30 proteins were detected in the pollination drops of both species. Many of these have been detected in the drops of other gymnosperms and probably function in defence, polysaccharide metabolism and pollen tube growth. Other proteins appear to be unique to Cephalotaxus, and their putative functions include starch and callose degradation, among others. Together, the proteins appear either to have been secreted into the drop or to occur there due to breakdown of ovular cells during drop production. Ovular transcripts represent a wide range of gene ontology categories, and some may be involved in drop formation, ovule development and pollen-ovule interactions. CONCLUSIONS: The proteome of Cephalotaxus pollination drops shares a number of components with those of other conifers and gnetophytes, including proteins for defence such as chitinases and for carbohydrate modification such as ß-galactosidase. Proteins likely to be of intracellular origin, however, form a larger component of drops from Cephalotaxus than expected from studies of other conifers. This is consistent with the observation of nucellar breakdown during drop formation in Cephalotaxus The transcriptome data provide a framework for understanding multiple metabolic processes that occur within the ovule and the pollination drop just before fertilization. They reveal the deep conservation of WUSCHEL expression in ovules and raise questions about whether any of the S-locus transcripts in Cephalotaxus ovules might be involved in pollen-ovule recognition.

Kin recognition within a seed and the effect of genetic relatedness of an endosperm to its compatriot embryo on maize seed development.

As one of two sexual products resulting from double fertilization in angiosperms, the endosperm nourishes its compatriot embryo during seed development and/or germination and ultimately dies. Theoretical studies suggest that the genetic relatedness of an endosperm to its embryo in the same seed might determine the amount of resources ultimately available for the embryo during seed development. We took advantage of the phenomenon of heterofertilization in cultivated maize to empirically test whether genetic relatedness between a triploid embryo-nourishing endosperm and its compatriot diploid embryo impacts the process of resource allocation between these two sexually produced entities. We used genetically distinct maize inbred lines to perform two crossing experiments. Dry weights of dissected embryos and endosperms of mature heterofertilized and adjacent homofertilized kernels were compared. Embryo weight of heterofertilized kernels was significantly less than that of embryos of homofertilized kernels, whereas there was no significant difference in endosperm weight between the two types of kernels. Our results suggest that the degree of genetic relatedness of an endosperm to its compatriot embryo affects seed development and specifically the amount of maternal resources allocated to an endosperm that are eventually turned over to an embryo. The lower the coefficient of relatedness of an endosperm to its compatriot embryo, the smaller the embryo. Thus, the endosperm of a heterofertilized seed appears to behave less cooperatively with respect to resource transfer toward its less closely related embryo compared with the endosperm of a homofertilized seed.

Spatial structuring of bacterial communities within individual Ginkgo biloba trees.

Plant-associated microorganisms affect the health of their hosts in diverse ways, yet the distribution of these organisms within individual plants remains poorly understood. To address this knowledge gap, we assessed the spatial variability in bacterial community diversity and composition found on and in aboveground tissues of individual Ginkgo biloba trees. We sampled bacterial communities from > 100 locations per tree, including leaf, branch and trunk samples and used high-throughput sequencing of the 16S rRNA gene to determine the diversity and composition of these communities. Bacterial community structure differed strongly between bark and leaf samples, with bark samples harbouring much greater bacterial diversity and a community composition distinct from leaves. Within sample types, we observed clear spatial patterns in bacterial diversity and community composition that corresponded to the samples' proximity to the exterior of the tree. The composition of the bacterial communities found on trees is highly variable, but this variability is predictable and dependent on sampling location. Moreover, this work highlights the importance of carefully considering plant spatial structure when characterizing the microbial communities associated with plants and their impacts on plant hosts.

Floral biology and ovule and seed ontogeny of Nymphaea thermarum, a water lily at the brink of extinction with potential as a model system for basal angiosperms.

BACKGROUND AND AIMS: Nymphaea thermarum is a member of the Nymphaeales, of one of the most ancient lineages of flowering plants. This species was only recently described and then declared extinct in the wild, so little is known about its reproductive biology. In general, the complete ontogeny of ovules and seeds is not well documented among species of Nymphaea and has never been studied in the subgenus Brachyceras, the clade to which N. thermarum belongs. METHODS: Flowers and fruits were processed for brightfield, epifluorescence and confocal microscopy. Flower morphology, with emphasis on the timing of male and female functions, was correlated with key developmental stages of the ovule and the female gametophyte. Development of the seed tissues and dynamics of polysaccharide reserves in the endosperm, perisperm and embryo were examined. KEY RESULTS: Pollen release in N. thermarum starts before the flower opens. Cell walls of the micropylar nucellus show layering of callose and cellulose in a manner reminiscent of transfer cell wall patterning. Endosperm development is ab initio cellular, with micropylar and chalazal domains that embark on distinct developmental trajectories. The surrounding maternal perisperm occupies the majority of seed volume and accumulates starch centrifugally. In mature seeds, a minute but fully developed embryo is surrounded by a single, persistent layer of endosperm. CONCLUSIONS: Early male and female function indicate that N. thermarum is predisposed towards self-pollination, a phenomenon that is likely to have evolved multiple times within Nymphaea. While formation of distinct micropylar and chalazal developmental domains in the endosperm, along with a copious perisperm, characterize the seeds of most members of the Nymphaeales, seed ontogenies vary between and among the constituent families. Floral biology, life history traits and small genome size make N. thermarum uniquely promising as an early-diverging angiosperm model system for genetic and molecular studies.

Development and evolution of the female gametophyte and fertilization process in Welwitschia mirabilis (Welwitschiaceae).

PREMISE OF THE STUDY: The female gametophyte of Welwitschia has long been viewed as highly divergent from other members of the Gnetales and, indeed, all other seed plants. However, the formation of female gametes and the process of fertilization have never been observed. METHODS: Standard histological techniques were applied to study gametophyte development and the fertilization process in Welwitschia. KEY RESULTS: In Welwitschia, fertilization events occur when pollen tubes with binucleate sperm cells grow down through the nucellus and encounter prothallial tubes, free nuclear tubular extensions of the micropylar end of the female gametophyte that grow up through the nucellus. Entry of a binucleate sperm cell into a vacuolate prothallial tube appears to stimulate the rapid coagulation of cytoplasm around a single female nucleus, which differentiates into an egg cell. One sperm nucleus enters the female gamete, while the second sperm nucleus remains outside and ultimately degenerates. Only a single fertilization event occurs per mating pair of pollen tube and prothallial tube. CONCLUSIONS: Welwitschia lacks the gnetalean pattern of regular double fertilization, as found in Ephedra and Gnetum, involving sperm from a single pollen tube to yield two zygotes. Moreover, an analysis of character evolution indicates that the female gametophyte of Welwitschia is highly apomorphic both among seed plants, and specifically within Gnetales, but also shares several key synapomorphies with its sister taxon Gnetum. Finally, the biological role of prothallial tubes in Welwitschia is examined from the perspectives of gamete competition and kin conflict.

Charles Darwin and the origins of plant evolutionary developmental biology.

Much has been written of the early history of comparative embryology and its influence on the emergence of an evolutionary developmental perspective. However, this literature, which dates back nearly a century, has been focused on metazoans, without acknowledgment of the contributions of comparative plant morphologists to the creation of a developmental view of biodiversity. We trace the origin of comparative plant developmental morphology from its inception in the eighteenth century works of Wolff and Goethe, through the mid nineteenth century discoveries of the general principles of leaf and floral organ morphogenesis. Much like the stimulus that von Baer provided as a nonevolutionary comparative embryologist to the creation of an evolutionary developmental view of animals, the comparative developmental studies of plant morphologists were the basis for the first articulation of the concept that plant (namely floral) evolution results from successive modifications of ontogeny. Perhaps most surprisingly, we show that the first person to carefully read and internalize the remarkable advances in the understanding of plant morphogenesis in the 1840s and 1850s is none other than Charles Darwin, whose notebooks, correspondence, and (then) unpublished manuscripts clearly demonstrate that he had discovered the developmental basis for the evolutionary transformation of plant form.

Physcomitrella cyclin-dependent kinase A links cell cycle reactivation to other cellular changes during reprogramming of leaf cells.

During regeneration, differentiated plant cells can be reprogrammed to produce stem cells, a process that requires coordination of cell cycle reactivation with acquisition of other cellular characteristics. However, the factors that coordinate the two functions during reprogramming have not been determined. Here, we report a link between cell cycle reactivation and the acquisition of new cell-type characteristics through the activity of cyclin-dependent kinase A (CDKA) during reprogramming in the moss Physcomitrella patens. Excised gametophore leaf cells of P. patens are readily reprogrammed, initiate tip growth, and form chloronema apical cells with stem cell characteristics at their first cell division. We found that leaf cells facing the cut undergo CDK activation along with induction of a D-type cyclin, tip growth, and transcriptional activation of protonema-specific genes. A DNA synthesis inhibitor, aphidicolin, inhibited cell cycle progression but prevented neither tip growth nor protonemal gene expression, indicating that cell cycle progression is not required for acquisition of protonema cell-type characteristics. By contrast, treatment with a CDK inhibitor or induction of dominant-negative CDKA;1 protein inhibited not only cell cycle progression but also tip growth and protonemal gene expression. These findings indicate that cell cycle progression is coordinated with other cellular changes by the concomitant regulation through CDKA;1.

Arabinogalactan proteins mark stigmatic receptivity in the protogynous flowers of Magnolia virginiana (Magnoliaceae).

PREMISE OF THE STUDY: Factors affecting floral receptivity in angiosperms remain opaque, but recent studies suggest that the acquisition of stigmatic receptivity associated with cell-wall-related arabinogalactan proteins (AGPs) may be a widespread feature of flowering plants. Here, the time during which a stigma is receptive is evaluated and related to the secretion of AGPs in Magnolia virginiana, a protogynous member of an early-divergent angiosperm clade (magnoliids) with a clearly discernible female receptive phase. METHODS: Magnolia virginiana flower phenology was documented, and histochemical changes in the stigma before and after pollination were examined. Stigmatic receptivity was evaluated in relation to the secretion of AGPs detected in whole mounts and immunolocalized in sectioned stigmas. KEY RESULTS: Protogynous Magnolia flowers had a precise window of stigmatic receptivity, which is concomitant with the secretion of two AGPs labeled for different epitopes. After pollen germination and tube growth, these two AGPs could no longer be detected in the stigmas, suggesting that these AGPs interact with the growing male gametophytes and could be markers of stigmatic receptivity. CONCLUSIONS: These results show that the period of stigmatic receptivity is finely coordinated with the secretion of two arabinogalactan proteins on stigmas of flowers of M. virginiana. This first report of AGP presence in stigmatic tissues in a member of the magnoliids, together with recently described similar patterns in eudicots, monocots, and members of early-divergent lineages of flowering plants, suggests an ancient and widespread role for AGPs on stigmatic receptivity in angiosperms.