Orobanchaceae
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
Mycoheterotrophs
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