dePamphilis, Claude W. [1], McNeal, Joel R. [2], Zhang, Yan [3], Cui, Liying [1], Kuehl, Jennifer V. [4], Boore, Jeffrey L. [4].
Plastid Genomes of Parasitic Plants: Distinct paths of evolution in independent heterotrophic lineages.
The sequenced plastid genomes of photosynthetic land plants have maintained a near constancy of gene content through hundreds of millions of years of evolutionary divergence. Parasitic and mycotrophic plants, many having lost photosynthetic ability, are valuable tools for understanding the forces that result in such apparent stability. The sequenced plastid genome of one parasite, Epifagus virginiana, has numerous deletions that have removed all photosynthetic and ndh genes, and a surprising set of plastid encoded genes for transcription and translation. It is unknown how general this outcome may be, and whether independent heterotrophic lineages convergently achieve a similar structure. We have sequenced the plastid genomes from four additional parasitic angiosperms that represent three independent lineages of heterotrophic plants: Conopholis americana (Orobanchaceae, as is Epifagus), Pholisma arenarium (Lennoaceae), and Cuscuta obtusiflora.and Cuscuta exaltata (Convolvulaceae). The gene content of Pholisma is strikingly similar to that of both Epifagus and Conopholis, suggesting almost complete convergence, except that a potentially functional rbcL gene has been retained only in Pholisma. Surprisingly, although the third heterotrophic lineage, Cuscuta, has undergone extensive gene loss, both species retain a nearly complete, and highly conserved set of photosynthetic protein genes. These observations have broad implications for chloroplast biology and gene function, mechanisms of genome evolution, and chloroplast phylogenetics.
1 - Pennsylvania State University, Department
of Biology and Institute of Molecular Evolutionary Genetics, University
Park, Pennsylvania, 16801, USA
2 - Arnold Arboretum at Harvard University, Cambridge,
Massachusetts, 02138, USA
3 - Pennsylvanian State University, Department
of Biology, University Park, Pennsylvania, 16802, USA
4 - DOE Joint Genome Institute, Department of Evolutionary
Genomics, 2800 Mitchell Drive, Walnut Creek, California, 94598,
USA
Keywords:
Chloroplast genome
Parasitic plants
Orobanchaceae
Lennoaceae
Cuscuta
Genome evolution.
Lim, Seok-Hong [1], Barkman, Todd J. [2].
An investigation of the prevalence of horizontal gene transfer in parasitic flowering plants.
Previously thought to be a rare phenomenon, observations of horizontal gene transfer (HGT) between unrelated plant lineages are accumulating. Although the mechanism of HGT is still unknown, the intimate association between endoparasites and their hosts may have facilitated many such horizontal transfers. To detect the prevalence of HGT across three independent lineages of endoparasites that parasitize completely different hosts, a total of eleven genes from different protein complexes from the mitochondrial genome were sequenced. Preliminary phylogenetic results suggest that at least three genes have undergone HGT in one or more of the three endoparasites. This study has implications for the use of mitochondrial genes in phylogenetic analyses as well as better understanding of the pattern(s) and process(es) of HGT among flowering plants.
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1 - Western Michigan University, Department of Biological
Sciences, 1903 West Michigan Ave, Kalamazoo, Michigan, 49008,
USA
2 - Western Michigan University, Department of Biological
Sciences, 3437 Wood Hall, Kalamazoo, Michigan, 49008, USA
Keywords:
HGT
Parasitic plants
mitochondrial genes.
Bolin, Jay F. [1], Maass, Erika [2], Musselman, Lytton John [1], Tennakoon, Kushan U. [3]. [POSTER]
Floral biology of three Namibian Hydnora (Hydnoraceae).
Hydnora is an understudied genus of root holoparasites with a primarily African distribution. The center of diversity is the Karoo-Namib region of Namibia and South Africa (H. abyssinica, H. africana, and H. triceps). Hydnora triceps is the only eudicot with hypogeous flowers and fruit, other Hydnora spp. flower at the soil surface. The protogynous chamber flowers bear osmophores and an actively closing antheral ring that can trap insects in the gynoecial chamber. Antheral ring imprisonment of insects varies from complete to partial among Hydnora spp. The active trapping mechanism may be functionally redundant to protogyny. Brood site mimicry with imprisonment and thermogeny is suspected. Up to 13 insects of several orders have been observed within a single H. africana flower. Proposed field experiments on the comparative floral biology of the group, thermogeny, and insect imprisonment are discussed.
1 - Old Dominion University, Department of
Biological Sciences, Mills Godwin Building, 45th Street, Norfolk,
Virginia, 23529-0266, USA
2 - University of Namibia, Department of Biology, Private
Bag 13301, Windhoek, , Namibia
3 - University of Peradeniya, Department of Botany,
Peradeniya, 20400, Sri Lanka
Keywords:
pollination
Holoparasite
Chamber Flower
Brood Site Mimicry.
Tennakoon, Kushan U. [1], Bolin, Jay F. [1], Musselman, Lytton John [1].[POSTER]
"Pilot Roots" of Hydnora triceps and H. africana (Hydnoraceae) are stems.
Achlorophyllous root holoparasites with extremely reduced vegetative bodies, Hydnora spp are the only known angiosperms with no leaves or scales. The vegetative body consists of "pilot roots", poorly studied structures bearing haustoria and flowers. Our studies show a "chimeral" apical structure and a protective layer of cells similar to a root cap at the growing tip. However, eustelic, endarch, and collateral vascular bundles and the continuous pith indicate "pilot roots" are stems. Increased girth is due to the fascicular cambium, periderm, and strands of cells distributed in the main vegetative body similar to a primary thickening meristem. The haustorium and the reproductive structures of Hydnora initiate exogenously from the "root bumps" (outgrowths of the vegetative body). An endophytic primordium penetrated the host root with a. stratified meristem giving rise to xylary and phloic hyphae, and transfer cells.
1 - Old Dominion University, Department of Biological Sciences, Mills Godwin Building, 45th Street, Norfolk, Virginia, 23529-0266, USA
Keywords:
root parasite
haustorium
morphogenesis.
Vidal-Russell, Romina [1], Nickrent, Daniel [1].
A molecular phylogeny of the mistletoe family Loranthaceae.
Loranthaceae is the largest mistletoe family with 73 genera and ca. 900 species with a pantropical distribution. Previous classifications based on floral morphology, inflorescences, and karyotype have been proposed, but no modern classification exists that includes all genera. The family comprises three tribes Elytrantheae (haploid base chromosome number of X=12), Lorantheae (X=9) and Psittacantheae (mostly X=8). The latter two base numbers are considered derived via aneuploid reduction. To elucidate the phylogeny of the family, we used sequences for 60 genera from chloroplast matK and nuclear small-subunit and large-subunit ribosomal DNA. Maximum parsimony analyses were performed on the matK partition and rDNA partitions separately and on both partitions combined. Four genera from Olacaceae were used as outgroups. Although the tree derived from the rDNA partition was less resolved than the matK tree, no major incongruences were detected. The tree obtained from the combined data placed the root parasite Nuytsia as sister to all other Loranthaceae. The other two root parasitic genera ( Atkinsonia and Gaiadendron) were part of a polytomy that included several well-supported clades as well as monotypic southern hemisphere genera. A group of eight New World X=8 genera is strongly supported as monophyletic. With present sampling (8 of 14 genera), tribe Elytrantheae appears to be monophyletic. The remaining strongly supported clade contains over 30 genera, mainly in tribe Lorantheae. Either Loranthus or an Ileostylus/Muellerina clade (New Zealand) is sister to the remaining genera. A clade of 18 African genera appears from a polytomy of Asian/Australian genera, but with low bootstrap support. The derived position of all African Loranthaceae conflicts with an interpretation of phylogeny based strictly on vicariance. Our data support the concept of relictual and ancestral genera being present in South America and Australia/New Zealand (Tupeia) with subsequent migration from the latter source to Asia, India, and Africa.
1 - Southern Illinois University, Department of Plant Biology, 1125 Lincoln Drive, Carbondale, Illinois, 62901-6509, USA
Keywords:
Biogeography
matK
ribosomal DNA.
Amico, Guillermo C. [1], Vidal-Russell, Romina [2], Nickrent, Daniel [2]. [POSTER]
Molecular Phylogeny of Tristerix (Loranthaceae).
The South American endemic mistletoe genus Tristerix (Loranthaceae) consists of eleven species with an andean distributed from Colombia to Chile. Tristerix has been divided into two subgenera, Tristerix (two species) and Metastachys (nine species). This classification was based mainly on the number of petals and the presence of bracteoles. The objective of this work was to reconstruct the phylogeny of the genus using molecular markers. Genomic DNA was extracted for all species except T. peruvianus and T. secundus. More than one individual was included for T. aphyllus, T. corymbosus and T. verticillatus. Three partitions were used for the molecular analysis: the internal transcriber spacer (ITS) of nuclear ribosomal DNA and two noncoding chloroplast spacers (atpB - rbcL and trnL - trnF). Three genera of South American Loranthaceae were used as outgroups. Separate maximum parsimony analyses of the three partitions resulted in congruent tree topologies, thus we conducted a combined analysis. Five subgenus Metastachys species formed a strongly supported clade. Two species (T. verticillatus and T. penduliflorus), previously considered part of Metastachys, were placed on a strongly supported clade with subgenus Tristerix species. Different Tristerix verticillatus accessions are paraphyletic using both chloroplast partitions but this relationship is not obtained with ITS. If a true conflict exists, hybridization with T. aphyllus or/and T. corymbosus is suggested. These three species share the same geographic range and a hummingbird pollen vector (Sephanoides sephaniodes).
1 - Universidad Nacional del Comahue, CRUB, Laboratorio
de Ecotono, Quintral 1250, Bariloche, RN, 8400, Argentina
2 - Southern Illinois University, Department of Plant Biology,
1125 Lincoln Drive, Carbondale, Illinois, 62901-6509, USA
Keywords:
trnT-L spacer
interspecific hybridization
ITS
mistletoe
atpB-rbcL spacer.
Der, Joshua [1], Nickrent, Daniel [1].
Molecular systematics of Santalaceae: phylogeny and classification of a paraphyletic family of hemiparasitic plants.
Santalaceae is a cosmopolitan family of root and stem hemiparasitic plants in the sandalwood order (Santalales). Santalaceae are paraphyletic with respect to Viscaceae and Eremolepidaceae and therefore these taxa were included in a broadly defined family by APG2. Previous classifications recognized Santalaceae sensu stricto (35 genera, ca. 440 species), which included four tribes (Amphorogyneae, Anthoboleae, Santaleae, and Thesieae), as well as Eremolepidaceae (three genera, 11 species) and Viscaceae (seven genera, 550 species). Phylogenetic analyses based on nuclear SSU rDNA and chloroplast rbcL and matK DNA sequences were performed on partitioned and combined datasets using maximum parsimony, maximum likelihood and Bayesian methods. Phylogenies inferred from separate gene partitions are congruent, but differ in their level of resolution. Seven well-supported clades are recovered in all analyses of the combined dataset. Deep-level relationships among many of these clades are ambiguous and have short branch lengths, possibly representing rapid radiation within the family. However, Bayesian analyses provide some support for a topology among these groups. Here we propose a new classification for santalaceous genera based on this phylogeny that recognizes seven families: Viscaceae, Amphorogynaceae, Santalaceae, Nanodeaceae, Pyrulariaceae, Thesiaceae, and Comandraceae. With respect to previous classifications, generic circumscription in Viscaceae and Amphorogynaceae remain intact and these are well-supported sister taxa. Eremolepidaceae is monophyletic and emerges as one clade from our revised Santalaceae. Santalaceae also includes a basal clade containing Exocarpos and Omphacomeria, formerly classified in tribe Anthoboleae. Anthobolus, however, is excluded from Santalaceae and allied with Opiliaceae. Three distinct clades (Nanodeaceae, Pyrulariaceae, and Comandraceae) are segregated from the polyphyletic tribe Santaleae and Buckleya and Kunkeliella are members of Thesiaceae. The placement of Arjona and Quinchamalium is uncertain, but these taxa may be allied with Thesiaceae where they have been traditionally classified.
1 - Southern Illinois University, Department of Plant Biology, 1125 Lincoln Drive, Carbondale, Illinois, 62901-6509, USA
Keywords:
nuclear ribosomal DNA
rbcL
matK
Eremolepidaceae
Opiliaceae
Viscaceae.
Nickrent, Daniel [1], Speicher, Katherine A. [1], Der, Joshua [1].
Phylogenetic Utility of Chloroplast Acetyl-CoA Carboxylase in Angiosperms.
Fatty acid biosynthesis in plants occurs within plastids and is carried out by two enzymes, acetyl-CoA carboxylase (ACCase) and fatty acid synthase. The former is extremely important in that it catalyzes the first committed step, the carboxylation of acetyl-CoA to malonyl-CoA. The heteromeric form of ACCase is composed of four subunits (BCCP, BC, aCT and bCT); the latter (b-carboxyltransferase) is encoded by the plastid gene accD and the remaining three subunits are nuclear encoded. Recent reviews have stated that accD is not present in monocots, however, it is apparently absent only in grasses. Primers were designed for the gene by first constructing a multiple sequence alignment of 28 angiosperm species. These were used to amplify a 1300 bp fragment of the 1620 bp gene for representatives of all major angiosperm orders and selected members of Santalaceae, a family chosen to test the phylogenetic utility of this gene among related genera. An alignment of rbcL sequences from the same suite of taxa was also constructed for comparative purposes. In total we analyzed 46 accD sequences (30 generated at SIUC, 16 obtained from GenBank). Although alignment across all angiosperms required the introduction of numerous gaps, the vast majority of sites were unambiguous when amino acid codon positions were taken into consideration. More parsimony informative sites were seen in accD (43%) as compared with rbcL (29%). Additionally, accD yields trees that have higher consistency indices than rbcL. Angiosperm clades recovered in other multigene analyses are seen on the accD tree, e.g. asterids, rosids, Caryophyllales, Santalales, and eudicots. Both genes provide similar levels of resolution for intergeneric relationships within Santalaceae. Thus, the accD gene compares favorably with rbcL , the most widely used chloroplast gene, and should be considered an excellent candidate for other molecular phylogenetic studies.
1 - Southern Illinois University, Department of Plant Biology, 1125 Lincoln Drive, Carbondale, Illinois, 62901-6509, USA
Keywords:
accD
rbcL
Santalaceae.
Nickrent, Daniel [1], Anderson, Frank [2], Der, Joshua [1].
Phylogenetic analyses identify the photosynthetic relatives of Cynomorium and Balanophoraceae.
Recent molecular phylogenetic work has helped place several nonphotosynthetic holoparasites such as Hydnoraceae and Rafflesiales within the overall angiosperm phylogeny. Two other holoparasitic groups, Cynomoriaceae and Balanophoraceae, are currently listed as "taxa of uncertain position" in APG2. Debate exists as to whether Cynomorium is a member of Balanophoraceae or whether it should be segregated into its own family. In either case, all classifications accept a close relationship between the two groups. We used nuclear, chloroplast, and mitochondrial gene sequence data, analyzed with maximum parsimony and Bayesian inference methods, to determine whether Balanophoraceae and Cynomoriaceae are related to one another and where they fit in the overall angiosperm phylogeny. Analysis of a four gene data set strongly supported the independent origin of these two families. Thus, the morphological features thought to link Cynomorium and some members of Balanophoraceae must be interpreted as convergent. Cynomorium is placed in Saxifragales with strong support whereas Balanophoraceae appear related to Santalales. The latter result is surprising because any morphological similarities have usually been assumed to be convergent. A five gene data set was used to determine the position of Cynomorium within Saxifragales. The shortest MP trees contained a clade composed of Cynomorium and Crassulaceae, however, this relationship did not receive high support. To pinpoint the exact sister group of Balanophoraceae within Santalales, additional sequence data is required. Cynomorium species are extensively used in herbal medicines and recent phytochemical and biomedical research has demonstrated physiological activity. Because all material is being collected from wild populations and because cultivation methods are currently unknown, overexploitation has resulted in localized extinctions. Identification of the photosynthetic relatives of Cynomorium would initiate work to determine whether these plants also contain compounds of biomedical interest, thus relieving pressure on the more sensitive parasitic species.
1 - Southern Illinois University, Department of Plant
Biology, 1125 Lincoln Drive, Carbondale, Illinois, 62901-6509,
USA
2 - Southern Illinois University, Department of Zoology,
Carbondale, Illinois, 62901, USA
Keywords:
holoparasitic angiosperm
Saxifragales
Santalales
herbal medicine
conservation
mitochondrial genes
nuclear genes
chloroplast genes.
Wolfe, Andrea D. [1], Arguedas, Nidia [1].
Identifying host plants of Hyobanche L. (Orobanchaceae) by DNA sequencing of host root tissue.
Hyobanche L. is a small genus of holoparasitic plants in southern Africa. Species of Hyobanche occur in a variety of habitats ranging from coastal sand dune scrub to deserts of the Karoo and Namaqualand to alpine rock outcrops and grasslands of the Drakensberg and Lesotho. Most of the biomass of this parasitic plant is underground in the form of fragile, branching rhizomes. The plant lacks a root system, but takes in water, mineral nutrients and reduced carbon from unique secondary leaf haustoria along the length of the rhizome, which are attached to host roots. Because the rhizomes are typically long, the inflorescence emerging above ground may be a considerable distance from the actual host plant. However, most host plants have been inferred in terms of their close proximity to the parasite inflorescence. It is extremely difficult to excavate an intact parasite rhizome system with the host root connections, which would lead to a positive identification of the host plant. To identify host plants of Hyobanche, rhizome systems were carefully excavated and the host root tissues attached to haustoria were collected for DNA extraction and sequencing. Positive identification of host plants included Chrysanthemoides, Metalasia, Passarina, Disparago, and Bromus.
1 - Ohio State University, Department of Ecology, Evolution, & Organismal Biology, 300 Aronoff Laboratory, 318 W. 12Th Avenue, Columbus, Ohio, 43210-1293, USA
Keywords:
Parasitic plants
Orobanchaceae
Hyobanche
host plant identification.
Tank, David [1], Olmstead, Richard [1].
Geographic disjunction or morphological convergence? The evolutionary origin of a second radiation of annual Castilleja species in South America (subtribe Castillejinae: Orobanchaceae).
Phylogenetic analyses of chloroplast (cp) and nuclear ribosomal (r) DNA sequence data has shown that the mostly perennial genus Castilleja has evolved from a grade of annual Castilleja species distributed chiefly in California. In addition to the North American annual species, a second geographic center of annual Castilleja species is in South America with seven annual species distributed in Chile and Andean Peru. The South American annuals are similar in both vegetative and reproductive morphology to those in North America, and are traditionally classified with the North American annual species in section Oncorhynchus. Based on previous morphological and cytological studies, it has been hypothesized that some of the six Peruvian annuals are allopolyploids involving hybridization of annual and perennial South American Castilleja species. Alternatively, this second radiation of annual species in South America may be derived from widely disjunct annual ancestors distributed in North America. Phylogenetic analyses of cpDNA, nuclear rDNA, and low-copy nuclear gene sequences have allowed us to test these competing hypotheses and determine whether the South American annual species are derived from disjunct annual ancestors, or are the result of in situ evolution, perhaps involving allopolyploidy, resulting in the same the same overall morphology.
1 - University of Washington, Department of Biology, Box 355325, Seattle, Washington, 98195-5325, USA
Keywords:
Castilleja
Orobanchaceae
allopolyploidy
low-copy nuclear genes
waxy.
Mohamed, Kamal [1], Peterson, A. Townsend [1].
Distributional Possibilities of Five Species of Striga in North America.
Concern is growing about the devastating effects that invasive noxious and parasitic plants may have on susceptible crops and the ecosystem in the United States. With this idea in mind, we used ecological niche modeling techniques (ENM) to predict the potential geographic distribution of 5 species of Striga in North America (S. asiatica, S. lutea, S. hirsuta, S. hermonthica, and S. gesnerioides). Among these species, the first three rank among the most destructive of all weed species worldwide. The ENM method employs known distributional data for the species in Africa in tandem with environmental GIS data layers to predict niche dimensions for each species in North America. In some cases, model predictions were complicated by presence of Striga species in irrigated situations outside their natural ranges in Africa. In other cases, models were complicated by host-specific strains within a species (e.g., S. gesnerioides). Results suggest that whereas S. lutea and S. hermonthica may not constitute a great concern to agriculture in North America, S. asiatica, S. gesnerioides, and S. hirsuta may have great potential to threaten agricultural crops because of their wide predicted geographic ranges. This result is consistent with already-known cases of S. asiatica and S. generioides in isolated areas in the southern United States. This risk evaluation-based on a quantitative and tested methodology -provides a framework within which management decisions may be developed.
1 - SUNY at Oswego, Biology, Oswego, New York, 13126
Keywords:
Striga
Scrophulariaceae
witchweed
S. asiatica
S. hermonthica
S. lutea.
SIUC / College of Science / Parasitic Plant Connection
URL: http://www.parasiticplants.siu.edu/meetings/Bot2005ParAbstracts.html
Last updated: 02-Aug-05 / dln