Abstracts Dealing with Parasitic Angiosperms and Mycoheterotrophs
Botany 2012
Columbus, OH USA

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Morawetz, Jeffery [1].

Comparative haustorial ultrastructure of hemiparasitic and holoparasitic Orobanchaceae.

The parasitic plant family Orobanchaceae presents an ideal system for studying the evolution of parasitism in plants. The family contains the full range of trophic capabilities from non-parasites to facultative and obligate hemiparasites and holoparasites. This parasiticability is conferred through an organ unique to parasitic plants: the haustorium. Direct xylem connections have been observed in all taxa examined;the width of the xylem bridge in haustoria is variable among the parasitic lineages in the family. However, a long-standing question about the structure of haustoria in Orobanchaceae remains unanswered: What are the structural modifications involved in phloem-to-phloem transfer between host and parasite? Here I examine the ultrastructure of two pairs of related taxa, each pair containing one hemiparasitic and one holoparasitic species. The proximity of host and parasite phloem differed between hemi- and holoparasites. The presence of transfer cells at the host-parasite interface, and plasmodesmatal connections between parasite and host cells at the interface will be discussed.

1 - Rancho Santa Ana Botanic Garden, 1500 North College Ave., Claremont, CA, 91711, USA

Rodrigues, Anuar [1], Stefanovic, Sasa [1].

Systematics and genetic diversity of the parasitic genus Conopholis (Orobanchaceae): Implications for classification and phylogeography.

Very little is known of the relationships among and between populations and species of Conopholis, one of approximately 20 holoparasitic genera in Orobanchaceae. Members of this small genus are obligate perennials with reduced vegetative morphology. In the most recent classification ofthe genus (1971), Conopholis is described as having two species, C. americana and C. alpina. Morphologically, this classification is based on a combination of presence/absence of characters, a number of quantitative traits, and the present day geographic isolation between taxa. In a recent molecular phylogenetic study of the genus, none of the analyses performed lend support to the strict subdivision of the genus into the two currently accepted species. Instead, the data provide strong support for three distinct lineages within the genus, each having various degrees of overlap with the two previously proposed taxa, thus lending support to the possibility of three species within Conopholis. We have since taken studies within this genus two-steps further. First, a fine-scale morphometric study was carried out to determine whether there are morphological features that corroborate these molecular results. Second, to investigate relationships between populations of C.americana s.l. (eastern North American species), we conducted phylogeographic and population level analyses to shed light on its genetic diversity and post glacial migration pattern(s). The findings of the morphological analyses supporting the recognition of three separate species within Conopholis as well as the population level differences within the eastern North American species will be discussed.

1 - University of Toronto Mississauga, Department of Biology, 3359 Mississauga Rd N, Mississauga, ON, L5L 1C6, Canada

Wicke, Susann [1], Mueller, Kai [1], Quandt, Dietmar [2], Wickett, Norman [3], dePamphilis, Claude [4], Schneeweiss, Gerald [5].

Broomrape plastid genomes reveal distinct patterns of functional and physical gene deletion under relaxed selective constraints.

Non-photosynthetic plants often possess highly reduced plastid chromosomes compared to their autotrophic relatives. As a result of the loss of autotrophy, genes involved in photosynthesis as well as protein-coding housekeeping genes are lost convergently in several unrelated lineages. Nevertheless, even 20 years after the first parasitic plant plastome had been sequenced, little is known about how functional and structural genome reduction takes place. In the present study,we trace the complex history of genome reduction in a group of closely related parasites of the broomrape family (Orobanchaceae). This group represents a wide array of intermediates in the process of plastome reduction that allows us to determine elementary patterns of deletion of dispensable DNA-fragments. To this end, we sequenced the plastid genomes from several photosynthetic and non-photosynthetic parasitic broomrape species. We thoroughly analyzed the structural evolution with respect to co-linearity, gene content, and functionality of genes. Using reconstructions of plastome rearrangements and ancestral gene content, we assessed molecular evolutionary patterns of gene loss and the deletion of DNA-segments under relaxed selective constraints. We provide convincing evidence that functional plastome reduction occurs in the early stages of heterotrophy, suggesting that the establishment of obligate parasitism can be viewed as the major, relaxed selective constraint en route to becoming non-photosynthetic. Increasing amounts of plastid repetitive DNA in parasites eventually entail increased rates of improper and/or illegitimate recombination leading to the eventual deletion of plastid-chromosomal fragments. Amongst others, our analyses reveal that the functional and physical plastome reduction coincides with a measurable increase in A/T-content in both coding and non-coding plastid DNA-fractions. Furthermore, we demonstrate that proximity to functionally relevant groups is the primary determinant of longevity and retention of dispensable genes and gene regions. By using an unprecedented comparative genomic approach, this study can provide detailed insights into the complex patterns of reductive evolution of plastomes under relaxed selective pressures.

1 - University of Muenster, Institute for Evolution and Biodiversity, Huefferstr. 1, Muenster, 48149, Germany
2 - University of Bonn, Nees Institute for Biodiversity of Plants, Meckenheimer Allee 170, Bonn, 53115, Germany
3 - Chicago Botanic Garden, Department Of Ecology & Evolutionary Biology, 5108 N Ashland Ave, Apt 2, Chicago, IL, 60640, USA
4 - Pennsylvania State University, Department Of Biology, 101 LIFE SCIENCES BUILDING, UNIVERSITY PARK, PA, 16802, USA
5 - University of Vienna, Department of Systematics and Evolutionary Botany, Rennweg 14, Vienna, 1030, Austria

Honaas, Loren [1], Wafula, Eric [1], Wickett, Norman [2], Zhang, Yeting [1], Zhang , Zhenzhen [1], Der, Joshua [1], Ralph, Paula [1], Landherr, Lena [1], Bao, Yongde [3], Wu, Biao [4], Gunathilake, Pradeepa [5], Fernandez-Aparicio, Monica [6], Das, Malay [6], Huang, Kan [7], Tomsho, Lynn P. [8], Schuster, Stephan C. [8], Taylor, Chris G.  [9], Altman, Naomi S.  [10], Yoder, John I.  [11], Timko, Michael P. [7], Westwood, James [6], dePamphilis, Claude [1].

The Parasitic Plant Genome Project.

Orobanchaceae are a plant family whose parasitic members include the devastating agricultural pests witchweed (Striga) and broomrape (Phelipanche). In addition to the pressing socioeconomic issues surrounding these parasites, this family represents a unique opportunity to study parasite biology since its members span varying degrees of parasitism from free-living to non-photosynthetic, obligate parasites. The Parasitic Plant Genome Project is taking a comparative evolutionary approach to understanding parasitism in the Orobanchaceae. The project has generated more than 1.5 billion expressed sequence tags (ESTs) from three species, a facultative parasite (Triphysaria versicolor), a photosynthetically competent obligate parasite (Striga hermonthica), and an obligate holoparasite (Phelipanche aegyptiaca). The de novo assemblies of these data represent all life stages from seed conditioning to flowering, and include approximately 30,000 unigenes for each species. In addition, ESTs (of whole-plant RNA) have been sequenced from the basal, non-parasitic Orobanchaceae species LIndenbergia philippensis, which is sister to all parasitic Orobanchaceae. The sequenced genome of another nonparasitic relative, Mimulus guttatus, is a useful reference to characterize genome wide changes associated with the transition from autotrophy to heterotrophy. The sequences are provided as a resource to the public in downloadable form and via a searchable database at http://ppgp.huck.psu.edu/. The results of this massive sequencing effort are shedding light on the biology and evolution of the Orobanchaceae. Transcriptome analysis has revealed striking patterns of gene expression including surprising conservation of photosynthetic machinery in the non-photosynthetic holoparasite Phelipanche, host specific responses by the generalist Triphysaria, stage-specific expression of a horizontally transferred gene in Phelipanche and identification of differentially expressed genes shared between all 3 species during phases of growth central to the parasitic lifestyle. The methods we have developed in the course of this work have broad application and the results underscore the potential to discover novel plant processes.
1 - Pennsylvania State University, Department of Biology, Institute of Molecular and Evolutionary Genetics and Huck Institutes for the Life Sciences, University Park, PA, 16802, USA
2 - Chicago Botanic Garden, 1000 Lake Cook Road, Glencoe, IL, 60022, USA
3 - University of Virginia, DNA Sciences Core - Department of Microbiology, Charlottesville, VA, 22903, USA
4 - University of California, Department of Plant Sciences, Davis, CA, 95616, USA
5 - University of Peradeniya, Department of Crop Science Faculty of Agriculture, 20400, Sri Lanka
6 - Virginia Polytechnic Institute and State University, Department of Plant Pathology, Physiology, and Weed Science, Blacksburg, VA, 24061, USA
7 - University of Virginia, Department of Biology, Charlottesville, VA, 22903, USA
8 - Pennsylvania State University, Department of Biochemistry and Molecular Biology, University Park, PA, 16802, USA
9 - Ohio State University, Department of Plant Pathology, Wooster, OH, 44691, USA
10 - Pennsylvania State University, Department of Statistics, University Park, PA, 16802, USA
11 - University of California, Department of Vegetable Crops, Davis, CA, 95616, USA

Convolvulaceae (Cuscuta)

Braukmann, Thomas [1], Kuzmina, Maria [2], Stefanovic, Sasa [1].

Fine-scale evolution of plastid genomes across Cuscuta (Convolvulaceae): Extensive loss of plastid genes within two clades of subgenus Grammica.

The genus Cuscuta, found within Convolvulaceae (the morning glory family), is one of the most investigated lineages of parasitic plants. Whole plastome sequencing of exemplar species within this genus has demonstrated changes to both plastid gene content and structure, but maintenance of photosynthetic and photorespiratory genes is observed. The presence of these genes under purifying selection indicates that Cuscuta is cryptically photosynthetic. However, plastid genome content across the diversity of this genus (~180 species) remains largely unknown. A fine-scale comparative investigation of plastid genome content, grounded within a phylogenetic framework, was conducted using a slot-blot Southern hybridization approach. We extensively sampled across Cuscuta, including within two clades (Kand O) previously reported to possess much more altered plastomes compared to other members of this genus. Fifty-six probes derived from all categories of protein coding genes typically found within the plastomes of flowering plants were used. Our results indicate that clades 'O' and 'K' exhibit far more plastid gene loss relative to other members of Cuscuta. All surveyed members of the 'O' clade show extensive loss of plastid genes from every category of genes typically found in the plastome, including otherwise highly conserved ribosomal subunits. The extent of plastid gene losses within this clade is similar to that observed in Rafflesiaceae in which the very presence of a plastome has previously been questioned. The 'K' clade also exhibits considerable loss of plastid genes. Unlike in the 'O' clade in which all species seem to be affected, the losses in this clade are progressive, culminating in C. erosa and C. strobilaceae. This presents an ideal opportunity to study the reduction of the plastome in holoparasites 'in action'. The widespread plastid gene loss in these two clades is hypothesized to be a consequence of the complete loss of photosynthesis. Additionally, we identify taxa that would be ideal for entire plastome sequencing to further investigate the loss of photosynthesis and reduction of the plastome within Cuscuta.
1 - University of Toronto Mississauga, Department of Biology, 3359 Mississauga Rd N, Mississauga, ON, L5L 1C6, Canada
2 - Canadian Center for DNA Barcoding, Guelph, ON

Wright, Michael [1], Ianni, Michael [2], Costea, Mihai [3].

Diversity and evolution of floral morphology and pollen/ovule production in Cuscuta (dodder, Convolvulaceae).

Cuscuta (dodder, Convolvulaceae) is a genus of obligate stem parasites with around 200 species distributed across temperate, subtropical and tropical regions worldwide. In order to build a broad picture of floral and mating system evolution, the diversity of floral morphology and pollen and ovule production was surveyed in 128 species and ten varieties. Taxa were assigned to Cruden's mating system categories based on their pollen-ovule ratios. Variation and correlations among floral characters were analyzed using regression and ANOVA, while the mating system categories were subjected to a linear discriminant and canonical variates analysis to assess their cohesiveness. Our data suggest that most Cuscuta species possess one of a wide range of mixed-mating systems. Whereas four ovules develop in each flower, pollen production varies over three orders of magnitude between taxa. Several Cuscuta taxa appear to be highly outcrossing, but no species could be identified that are exclusively selfing. The role of herkogamy as a facilitator of outcrossing has decreased in two phases: first, the transition from the one-style flowers of subgenus Monogynella to the two-style flowers of subgenera Cuscuta and Grammica, and second from simultaneous to sequential maturation of the two stigmas in subgenus Grammica. These evolutionary changes are associated with an increase of species richness in subgenus Cuscuta, and especially in subgenus Grammica. Morphological features were not individually found to have a strong correlation to the mating system, but in general larger corollas and stigmas were associated with greater pollen-ovule ratios. When considered in light of the sex allocation theory, Cuscuta presents some puzzling results. Only some infrageneric lineages demonstrate the predicted pollen size-number tradeoff, while Cuscuta gracillima complex (in subgenus Grammica) displays an unexpected negative relationship between pollen size and style length. The relationship between host ranges and mating systems will be discussed, highlighting opportunities for further research into the co-evolution of pollination systems and life history traits between parasitic plants and their host species.
1 - University of Toronto, Ecology & Evolutionary Biology/UTM Biology, 3359 Mississauga Road N, Mississauga, ON, L5L1C6, Canada
2 -
3 - Wilfrid Laurier University, Biology, 75 University Ave W, Waterloo, ON, N2L3C5, Canada

Riviere, Stephanie [1], Clayson, Courtney [1], Dockstader, Kristy [2], Wright, Michael [3], Costea, Mihai [4].

To attract or to repel? Function, diversity and evolution of infrastaminal scales in Cuscuta (dodders, Convolvulaceae).  – POSTER

Cuscuta (dodder, Convolvulaceae) is a genus of about 200 species of obligate stem parasites with subcosmopolitan distribution. Infrastaminal scales (IFS) are staminode-like formations that surround the ovary in the flowers of dodders. Their morphological diversity has historically provided some of the most useful taxonomic characters at the species-level, however, their function had not been determined. We have performed a comparative study of the IFS in 147 taxa using light, scanning and transmission electron microscopy, and results were analyzed in relation to a Cuscuta phylogeny obtained from a combined analysis of rbcL and 26S rDNA gene sequences. To test the hypothesis that the role of IFS is to attract pollinators, we analyzed the correlations between IFS characters and the production of pollen/ovules in the flower as an indicator of breeding systems. With a few exceptions, the IFS exhibit numerous fimbriae that contain laticifer cells secreting a complex resin-glycoside latex. In subgenus Monogynella, the first diverged infrageneric lineage, laticifer cells are exposed and fimbriae are similar to uniseriate glandular hairs. In the derived subgenera Grammica and Cuscuta, laticifers are enclosed and protected by an epidermis but leaving the distal ends of the laticifers exposed. Ultrastructurally, epidermal cells are connected among themselves and with the laticifer cells through plasmodesmata. The slightest mechanical contact with the exposed part of the laticifer cells (for example by an insect) causes them to burst open and release the latex. However, their putative role in attracting pollinators is not confirmed because the IFS and pollen/ovule ratios are not correlated. From a developmental point of view, IFS are the last structures to form in the flower and they persist after the fertilization, which strongly suggests that they play a role in the protection of the developing ovary/capsule against herbivorous insects. In three of the fifteen clades of subgenus Grammica, IFS have undergone a reduction trend, and in some species they are completely absent. In Clade O from the same subgenus, we observed papillae on the fimbriae, a feature that appears to be an apomorphy. Our study further details the morphological diversity of the IFS in Cuscuta, confirming their significance for the species-level systematics.
1 - Wilfrid Laurier University, Biology, 75 University Avenue West, Waterloo, ON, N2L3C5, CA
2 - Wilfrid Laurier University, 75 University Avenue West, Waterloo, ON, N2L3C5, CA
3 - University of Toronto, Ecology & Evolutionary Biology/UTM Biology, 3359 Mississauga Road N, Mississauga, ON, L5L1C6, Canada
4 - Wilfrid Laurier University, Biology, 75 University Ave W, Waterloo, ON, N2L3C5, Canada


Peterson, Larry [1].

Mycoheterotrophy - unique development between achlorophyllous plants, fungi, and autotrophic hosts.

Although most plants use chlorophyll to convert the sun's energy into metabolites for growth and reproduction, approximately 400 plant species within 87 genera and 10 families lack chlorophyll. Most of these species receive all of their carbon in the form of sugars from autotrophic plants via fungal connections and are therefore referred to as mycoheterotrophs. Since the fungus and the autotrophic host do not receive obvious benefits from the mycoheterotroph these plants are cheaters or exploitive mycorrhizas. The majority of achlorophyllous monocotyledonous species are associated with arbuscular mycorrhizal fungi forming the Paris-type colonization pattern. One monocot species, Arachnitis uniflora, has several unique features in the colonization process. As well, this species forms root-borne propagules that become colonized with fungi from the parent root before they detach. The monocot family, Orchidaceae, has the largest number of mycoheterotrophic species; these are associated with ectomycorrhizal fungi. In nature, all orchid species require a fungal symbiont for germination of their 'dust seeds' and for early seedling development. Ten genera in the Monotropoideae (Ericaceae) rely on ectomycorrhizal fungi connected to photosynthetic tree species for their source of carbon. These fungi form typical ectomycorrhizas with tree partners but unusual nutrient exchange interfaces with the mycoheterotroph. All mycohetertroph species demonstrate examples of close co-ordinated development between eukaryotic symbionts.
1 - University of Guelph, Molecular and Cellular Biology, 50 Stone Rd East, Guelph, ON, N1G 2W1, Canada

Jolles, Diana [1], Wallace, Gary [2].

Character evolution and phylogenetic relationships among species of Monotropeae and Pterosporeae (Monotropoideae: Ericaceae).

Phylogenetic relationships among species of subfamily Monotropoideae have been proposed based on nucleotide sequence data, but the position of Cheilotheca, a rarely collected southeast Asian genus containing two species, remains unknown. Generally, adequate material of all taxa within Monotropoideae has been difficult to assemble for comparison. Consequently, character evolution in Monotropoideae is also poorly understood. We used nucleotide sequencing of nuclear ITS and the plastid trnL-rpl32F region to test relationships among taxa within Monotropoideae, including Cheilotheca khasiana. In light of phylogenic patterns, we considered the evolution of several characters that differentiate species and genera within tribes Monotropeae and Pterosporeae. Finally, we propose some nomenclatural changes based on a combination of both molecular and morphological synapomorphy.
1 - Rancho Santa Ana Botanic Garden, Claremont Graduate University, 1500 North College Avenue, Claremont, CA, 91711, USA
2 - Rancho Santa Ana Botanic Garden, 1500 North College Avenue, Claremont, CA, 91711-3101, USA

Jolles, Diana [1].

How is reproductive isolation maintained in the Pyrola picta species complex, a group of species with remarkably similar flowers?

The Pyrola picta species complex (Monotropoideae: Ericaceae) is composed of at least four species that are restricted to western North America. These species have remarkably similar floral morphology and phenology given the fact that genetic lineages have largely achieved (and maintained) reproductive isolation across shared biogeographic ranges. In this study, maintenance of reproductive isolation was investigated in the context of lineage dispersal history by observing pollinators, recording aspects of flowering phenology, and conducting experimental crosses among species in multiple, sympatric populations in northern California. Findings suggest that, despite the fact that different species share the same pollinators (Bombus species), basic floral morphology, and buzz-pollination syndrome, low levels of hybridization in sympatric populations are associated with subtle differences in floral phenology and significantly different rates of fertilization in response to experimental crosses.
1 - Rancho Santa Ana Botanic Garden, Claremont Graduate University, 1500 North College Avenue, Claremont, CA, 91711, USA

Rothacker, Erik [1], Lehman, Jeffery  [1], Conard, Cameron  [2].

Utility of Large Inverted Repeat B primerson the amplification and the measurement of rates of evolution in chlorophyllous and achlorophyllous orchids.

Chloroplast loci are routinely used to determine the phylogenetic relationships of plants. Many loci in this genome function in photosynthesis and are evolutionarily conserved therefore mutations in the chloroplast genome can result in a loss of function. Orchids are parasitic on fungi for at least some portion of their life histories. The tribes of the basal Epidendroideae are mixotriophic with many becoming achlorophyllous and holoparasitic. Previous studies have pointed out that achlorophyllous plants in general exhibit higher TI/TV mutations and are therefore evolving at higher rates then photosynthetic sister taxa. When plants loose chlorophyll, functional constraints on the chloroplast genome are relaxed and should therefore exhibit increased mutation rates. The results can be that primer-binding sites for chloroplast loci may be lost. Numerous previous attempts to amplify chloroplast genes in these orchids using traditional primer sets have failed and there is a need for new primers. The objective of this research is to amplify, assess the phylogenetic utility of the Large Inverted Repeat B region and determine rates of chloroplast evolution in achlorophyllous orchid species and whether achlorophyllous taxa exhibit greater variability than chlorophyllous orchids. Taxa sampled from different genera, representing tribes ofthe basal Epidendroideae were amplified with primers designed for the IRB and sequenced. Analysis indicates that achlorophyllous orchids do possess these loci and that they contain phylogenetic signal and exhibit size variation when compared to green relatives.
1 - Otterbein University, Department of Biology and Earth Science, 1 South Grove St. , Westerville , OH, 43081, USA

2 - Otterbein University, Department of Biology and Earth Science, 1 South Grove St., Westerville , OH, 43081, USA

SIUC / College of Science / Parasitic Plant Connection
URL: http://www.parasiticplants.siu.edu/meetings/Bot2012ParAbstracts.html
Last updated: 29-Oct-12 / dln