Browsing by Subject "SEQUENCES"

Now showing 1 - 8 of 8
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    Comparative morphology of reproductive structures in heterosporous water ferns and a reevaluation of the sporocarp
    (International Journal of Plant Sciences, 2006-07-01) Nagalingum, NS; Schneider, H; Pryer, KM
    Heterosporous water ferns (Marsileaceae and Salviniaceae) are the only extant group of plants to have evolved heterospory since the Paleozoic. These ferns possess unusual reproductive structures traditionally termed "sporocarps." Using an evolutionary framework, we critically examine the complex homology issues pertaining to these structures. Comparative morphological study reveals that all heterosporous ferns bear indusiate sori on a branched, nonlaminate structure that we refer to as the sorophore; this expanded definition highlights homology previously obscured by the use of different terms. By using a homology-based concept, we aim to discontinue the use of historically and functionally based morphological terminology. We recognize the sorophore envelope as a structure that surrounds the sorophore and sori. The sorophore envelope is present in Marsileaceae as a sclerenchymatous sporocarp wall and in Azolla as a parenchymatous layer, but it is absent in Salvinia. Both homology assessments and phylogenetic character-state reconstructions using the Cretaceous fossil Hydropteris are consistent with a single origin of the sorophore envelope in heterosporous ferns. Consequently, we restrict the term "sporocarp" to a sorophore envelope and all it contains. Traditional usage of "sporocarp" is misleading because it implies homology for nonhomologous structures, and structures historically called sporocarps in Salviniaceae are more appropriately referred to as sori. © 2006 by The University of Chicago. All rights reserved.
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    Integrative Regulatory Mapping Indicates that the RNA-Binding Protein HuR Couples Pre-mRNA Processing and mRNA Stability
    (MOLECULAR CELL, 2011-08-05) Mukherjee, Neelanjan; Corcoran, David L; Nusbaum, Jeffrey D; Reid, David W; Georgiev, Stoyan; Hafner, Markus; Ascano, Manuel; Tuschl, Thomas; Ohler, Uwe; Keene, Jack D
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    Molecular phylogenetic relationships and morphological evolution in the heterosporous fern genus Marsilea
    (Systematic Botany, 2007-01-01) Nagalingum, NS; Schneider, H; Pryer, KM
    Using six plastid regions, we present a phylogeny for 26 species of the heterosporous fern genus Marsilea. Two well-supported groups within Marsilea are identified. Group I includes two subgroups, and is relatively species-poor. Species assignable to this group have glabrous leaves (although land leaves may have a few hairs), sporocarps lacking both a raphe and teeth, and share a preference for submerged conditions (i.e., they are intolerant of desiccation). Group II is relatively diverse, and its members have leaves that are pubescent, sporocarps that bear a raphe and from zero to two teeth, and the plants are often emergent at the edges of lakes and ponds. Within Group II, five subgroups receive robust support: three are predominantly African, one is New World, and one Old World. Phylogenetic assessment of morphological evolution suggests that the presence of an inferior sporocarp tooth and the place of sporocarp maturation are homoplastic characters, and are therefore of unreliable taxonomic use at an infrageneric level. In contrast, the presence of a raphe and superior sporocarp tooth are reliable synapomorphies for classification within Marsilea. © Copyright 2007 by the American Society of Plant Taxonomists.
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    On the phylogenetic position of Cystodium: It's not a tree fern - It's a polypod!
    (American Fern Journal, 2006-04-01) Korall, P; Conant, DS; Schneider, H; Ueda, K; Nishida, H; Pryer, KM
    The phylogenetic position of Cystodium J. Sm. is studied here for the first time using DNA sequence data. Based on a broad sampling of leptosporangiate ferns and two plastid genes (rbcL and atpB), we show that Cystodium does not belong to the tree fern family Dicksoniaceae, as previously thought. Our results strongly support including Cystodium within the large polypod clade, and suggest its close relationship to the species-poor grade taxa at the base of the polypod topology (Sphenomeris and Lonchitis, or Saccoloma in this study). Further studies, with an expanded taxon sampling within polypods, are needed to fully understand the more precise phylogenetic relationships of Cystodium.
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    Species relationships and farina evolution in the cheilanthoid fern genus Argyrochosma (Pteridaceae)
    (Systematic Botany, 2011-07-01) Sigel, EM; Windham, MD; Huiet, L; Yatskievych, G; Pryer, KM
    Convergent evolution driven by adaptation to arid habitats has made it difficult to identify monophyletic taxa in the cheilanthoid ferns. Dependence on distinctive, but potentially homoplastic characters, to define major clades has resulted in a taxonomic conundrum: all of the largest cheilanthoid genera have been shown to be polyphyletic. Here we reconstruct the first comprehensive phylogeny of the strictly New World cheilanthoid genus Argyrochosma. We use our reconstruction to examine the evolution of farina (powdery leaf deposits), which has played a prominent role in the circumscription of cheilanthoid genera. Our data indicate that Argyrochosma comprises two major monophyletic groups: one exclusively non-farinose and the other primarily farinose. Within the latter group, there has been at least one evolutionary reversal (loss) of farina and the development of major chemical variants that characterize specific clades. Our phylogenetic hypothesis, in combination with spore data and chromosome counts, also provides a critical context for addressing the prevalence of polyploidy and apomixis within the genus. Evidence from these datasets provides testable hypotheses regarding reticulate evolution and suggests the presence of several previously undetected taxa of Argyrochosma. © 2011 by the American Society of Plant Taxonomists.
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    Structure and function of spores in the aquatic heterosporous fern family Marsileaceae
    (International Journal of Plant Sciences, 2002-01-01) Schneider, H; Pryer, KM
    Spores of the aquatic heterosporous fern family Marsileaceae differ markedly from spores of Salviniaceae, the only other family of heterosporous ferns and sister group to Marsileaceae, and from spores of all homosporous ferns. The marsileaceous outer spore wall (perine) is modified above the aperture into a structure, the acrolamella, and the perine and acrolamella are further modified into a remarkable gelatinous layer that envelops the spore. Observations with light and scanning electron microscopy indicate that the three living marsileaceous fern genera (Marsilea, Pilularia, and Regnellidium) each have distinctive spores, particularly with regard to the perine and acrolamella. Several spore characters support a division of Marsilea into two groups. Spore character evolution is discussed in the context of developmental and possible functional aspects. The gelatinous perine layer acts as a flexible, floating organ that envelops the spores only for a short time and appears to be an adaptation of marsileaceous ferns to amphibious habitats. The gelatinous nature of the perine layer is likely the result of acidic polysaccharide components in the spore wall that have hydrogel (swelling and shrinking) properties. Megaspores floating at the water/air interface form a concave meniscus, at the center of which is the gelatinous acrolamella that encloses a "sperm lake". This meniscus creates a vortex-like effect that serves as a trap for free-swimming sperm cells, propelling them into the sperm lake.
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    The paraphyly of Osmunda is confirmed by phylogenetic analyses of seven plastid loci
    (Systematic Botany, 2008-03-01) Metzgar, JS; Skog, JE; Zimmer, EA; Pryer, KM
    To resolve phylogenetic relationships among all genera and subgenera in Osmundaceae, we analyzed over 8,500 characters of DNA sequence data from seven plastid loci (atpA, rbcL, rbcL-accD, rbcL-atpB, rps4-trnS, trnG-trnR, and trnL-trnF). Our results confirm those from earlier anatomical and single-gene (rbcL) studies that suggested Osmunda s.l. is paraphyletic. Osmunda cinnamomea is sister to the remainder of Osmundaceae (Leptopteris, Todea, and Osmunda s.s.). We support the recognition of a monotypic fourth genus, Osmundastrum, to reflect these results. We also resolve subgeneric relationships within Osmunda s.s. and find that subg. Claytosmunda is strongly supported as sister to the rest of Osmunda. A stable, well-supported classification for extant Osmundaceae is proposed, along with a key to all genera and subgenera. © Copyright 2008 by the American Society of Plant Taxonomists.
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    Toward a monophyletic Notholaena (Pteridaceae): Resolving patterns of evolutionary convergence in xeric-adapted ferns
    (Taxon, 2008-01-01) Rothfels, CJ; Windham, MD; Grusz, AL; Gastony, GJ; Pryer, KM
    Cheilanthoid ferns (Pteridaceae) are a diverse and ecologically important clade, unusual among ferns for their ability to colonize and diversify within xeric habitats. These extreme habitats are thought to drive the extensive evolutionary convergence, and thus morphological homoplasy, that has long thwarted a natural classification of cheilanthoid ferns. Here we present the first multigene phylogeny to focus on taxa traditionally assigned to the large genus Notholaena. New World taxa (Notholaena sensu Tryon) are only distantly related to species occurring in the Old World (Notholaena sensu Pichi Sermolli). The circumscription of Notholaena adopted in recent American floras is shown to be paraphyletic, with species usually assigned to Cheilanthes and Cheiloplecton nested within it. The position of Cheiloplecton is particularly surprising - given its well-developed false indusium and non-farinose blade, it is morphologically anomalous within the "notholaenoids". In addition to clarifying natural relationships, the phylogenetic hypothesis presented here helps to resolve outstanding nomenclatural issues and provides a basis for examining character evolution within this diverse, desert-adapted clade.