Abstracts Dealing with Parasitic
Angiosperms
Botany 2006
Chico, CA USA, July 28 to August 2, 2006
Click HERE to search all abstracts at this meeting
Abstracts of Oral Presentations and Posters
Arranged Taxonomically
Parasitic Plants in General (1)
Shyu, Shin-Yi, Hu, Jer-Ming. Studies
of plastid 16S rDNA suggest that the evolutionary rates vary among
nonphotosynthetic plants. Nonphotosynthetic plants usually retain a
reduced plastid genome, although most of the photosynthesis-related
genes are lost or become pseudogenes. In order to elucidate the plastid
genome evolution in non-photosynthetic plants, we examined
plastid-derived 16S rDNAs of nine nonphotosynthetic plants, including
some with partial photosynthetic ability. The 16S rDNA sequences from
all examined taxa were included in a phylogenetic analysis with other
land plants and green algae to show their relationships. To evaluate
rate heterogeneity among various 16S rDNA sequences, a relative rate
tests was conducted. Compared with other angiosperms, the 16S rDNA
sequences show an increasing substitution rates in four
nonphotosynthetic species: Balanophora laxiflora, Mitrastemon
kanehirai, Cheilotheca humilis and Cheilotheca macrocarpa. However the
other five species, Aeginetia indica, Cassytha filiformi, Cuscuta
australis, Galeola lindleyana, and Orobanche coerulescens, exhibited
only slightly higher rates relative to most angiosperms. Some of the
high sequence divergences are accompanied by an increase in A+T content
of the sequences, especially in M. kanehirai, which has the highest
rate among the examined taxa. In species with higher evolutionary rates
of 16S rDNAs, B. laxiflora, M. kanehirai are holoparasites and C.
humilis, C. macrocarpa are mycoheterotrophs. Theses plants have
completely lost their photosynthetic ability. However, among the other
five species examined, C. filiformi is a hemiparasitic plant and can
photosynthesize itself; G. lindleyana and young stage of C. australis
are slight green and maybe retain some photosynthetic ability. Although
A. indica and O. coerulescens are holoparasitc plants, Orobanchaceae
parasites lost their photosynthetic ability recently, and may not have
enough time to accumulate variations.
Link to Abstract on BSA website
Hydnoraceae (2)
Bolin, Jay F., Tennakoon, Kushan U., Musselman, Lytton John, Maass, Erika.
Germination and seedling development of the highly modified root
holoparasite Hydnora triceps. Hydnora (Hydnoraceae) is a small
genus of root holoparasites native to Africa, the southern Arabian
Peninsula and Madagascar. The most unusual of the group, the furtive H.
triceps, resides and flowers completely underground and exclusively
parasitizes Euphorbia dregeana. We present the results of the first
successful seed germination for the genus. The permeable seeds of H.
triceps required host root exudates of E. dregeana to germinate and did
not respond to root exudates from other Euphorbia spp. or control
treatments. Anatomical studies (light microscopy and SEM) revealed that
seeds of H. triceps have spherical undeveloped embryos in the center of
a large endosperm. Germination occurred when a cylindrical mass of
tissues originated from the embryo and emerged through the testa to a
length of 2-3 mm. ‘Germ tube’ rather than radicle or
hypocotyl was used to describe the cylindrical protrusion due to the
lack of well defined vascular tissue. This study also addresses
inconsistent terminology/interpretations encountered in the literature
for seedlings of highly modified holoparasites.
Link to Abstract on BSA website
Bolin, Jay F., Musselman, Lytton John, Maass, Erika. The
generalist pollination syndrome of the root holoparasite Hydnora
africana and a test of a selective insect trapping mechanism.
Hydnora africana (Hydnoraceae) is a root holoparasite of southern
Africa that parasitizes a variety of shrubby Euphorbia spp. The
trimerous flowers of H. africana are comprised of an androecial and
gynoecial chamber. Flowers are putatively protogynous (carpellate for 3
days) and produce a fetid odor from osmophores recessed on their
interior tepal surfaces. Within the flowers of H. africana we observed
18 insect species and several other non-insect floral visitors at two
sites in southern Namibia. The hide beetle Dermestes maculatus
accounted for 65% of the floral visitors observed. Glabrous and waxy
inner surface of the androecial chamber was selective; it prevented the
escape of small beetles but was not a barrier to ants, grasshoppers,
roaches, or large beetles. A beetle addition experiment (n = 8) using
D. maculatus was used to evaluate the trapping mechanism of H.
africana. Beetles began to escape the day pollen was shed due to
changes in the androecial wall. Beetle escape was 31.1 (± 19.2),
42.2 (± 17.1), and 55.5 (± 16.7) % for 1-3 days after
pollen shed, respectively. Pollen was still viable 72 hours after
shedding. This suggests that the trapped beetles can be effective
pollinators after escape.
Link to Abstract on BSA website
Loranthaceae (2)
Amico, Guillermo C., Nickrent, Daniel. Phylogeography
of the mistletoe Tristerix corymbosus (Loranthaceae) inferred from
chloroplast DNA sequences. The mistletoe Tristerix corymbosus is
distributed from 30º S in Chile to 42º S in Chile and
Argentina. Throughout this range this species is present in two
habitats, the temperate forest and the more recent Chilean matorral
which formed ca. 5 mybp. We examined chloroplast sequence variation
among populations covering the entire range of the species. Given the
recency of the matorral habitat, we postulate that mistletoe
populations found here have derived from forest populations. To test
this hypothesis we conducted molecular analyses of two non-coding
chloroplast regions: the atpB–rbcL spacer and the trnT-L-F
region. A network was constructed with statistical parsimony and
phylogenetic relationships between haplotypes were assessed using
parsimony, likelihood and Bayesian analyses. The trnT-L-F region is
less informative than the atpB-rbcL spacer; hence only one individual
per populations was sequenced from it. Sequences for the atpB-rbcL
spacer were obtained from 108 individual in 26 populations. The network
structure for both chloroplast regions was congruent. For the
atpB–rbcL spacer, eight haplotypes were identified that did not
correspond simply to matorral and forest types, but were placed in
three clades (here designated A, B, C). Only three populations had more
than one haplotype. Several phenomena at different geological times may
have influenced the present spatial pattern and genetic differentiation
of T. corymbosus populations. The uplift of the Andes had a great
impact, first dividing a widespread ancestral haplotype (clade A).
After glaciations, one of the clade B haplotypes may have dispersed
south from refugia in central Chile. Although the original hypothesis
was confirmed, the northernmost matorral populations of clade C were
most similar to the forest populations (not the geographically closer
southern ones), thus indicating the presence of a northern refugium.
These localities have already been inferred to be refugia for other
plants and animals.
Link to Abstract on BSA website
Wilson, C., Calvin, C. Origin
of Aerial Parasitism in the Loranthaceae. The large mistletoe family,
Loranthaceae, contains 75 genera and approximately 1000 species. The
family originated in the Southern Hemisphere and dispersed, apparently
early, between fragments of Gondwana. It is now widely distributed on
land surfaces of the former supercontinent. The Loranthaceae has three
terrestrial, root-parasitic genera—a habit considered
ancestral—and 72 genera of aerial, branch parasites. For almost
two centuries, the origin of the mistletoe habit has been of interest
to biologists. Two main evolutionary pathways have been proposed to
explain the transition from terrestrial to aerial parasitism in the
family. One theorizes the presence of an intermediate climbing ancestor
in the path to the aerial habit. The other proposes a direct transfer
from terrestrial to epiphytic growth following the germination of seeds
on tree branches. We present molecular and morphological evidence that
aerial parasitism has originated multiple times in the family, and that
the origin of aerial parasitism in one Old World clade resulted from
the direct transfer from terrestrial to epiphytic growth following the
germination of seeds on tree branches. Our results argue against the
currently preferred hypothesis that aerial Santalales necessarily
evolved from climbing ancestors.
Link to Abstract on BSA website
Misodendraceae (2)
Vidal-Russell, Romina, Nickrent, Daniel.
A Molecular Phylogeny of the Feathery Mistletoe Misodendrum
(Misodendraceae). Misodendrum comprises eight species of aerial
hemiparasite shrubs endemic to temperate forests of Chile and Argentina
from 33º S to 55º S. All parasitize Nothofagus, however, host
ranges vary among the species. Misodendrum can be distinguished from
all other mistletoes by the presence of achenes with feathery
staminodes that are wind dispersed. Previous classifications (Orfila
1978, Rossow 1982) included two subgenera, Misodendrum (two sections)
and Angelopogon (three sections). Our project tested this
classification using molecular markers: nuclear ITS rDNA and two
chloroplast genes (trnL-F and matK). All species except the rare M.
macrolepis were sampled. Maximum parsimony, likelihood and Bayesian
analyses were performed for individual and combined partitions. Other
molecular work in our lab has shown that Misodendraceae is sister to
Loranthaceae, thus this taxon was used as an outgroup. Results from
analyses of the separate partitions were generally congruent, differing
only in the position of M. linearifolium and M. quadriflorum; however,
the 3-gene tree gave higher support for M. quadriflorum as sister to
all other species. Misodendrum brachystachyum and M. oblongifolium form
a well supported clade that is sister to one composed of M.
punctulatum, M. gayanum and M. angulatum. This clade is sister to M.
linearifolium. These phylogenetic relationships generally agree with
previous classifications. Subgenus Misodendrum, characterized by warty
stems and two stamens, here resolves as a polytomy: M. punctulatum, M.
gayanum and M. angulatum (and likely M. macrolepis). Subgenus
Angelopogon, characterized by the plesiomorphies three stamens and
foliacious bracts, is paraphyletic given our rooting. Misodendrum
brachystachyum and M. oblongifolium (section Archiphyllum) differ
morphologically only by the length of their fruiting staminodes. M.
oblongifolium is restricted to northern Patagonia where it parasitizes
trees at higher elevations than the widespread M. brachystachyum. Our
data suggest that M. oblongifolium could be considered a variety of M.
brachystachyum.
Link to Abstract on BSA website
Vidal-Russell, Romina, Nickrent, Daniel.
Misodendraceae: the first aerial parasites of Santalales. Molecular
phylogenetic investigations have provided information on the
relationships among the families of Santalales. The order contains five
monophyletic families (Loranthaceae, Misodendraceae, Schoepfiaceae,
Opiliaceae and Viscaceae) and two polyphyletic families
(“Olacaceae” and “Santalaceae”). Olacaceae s.
lat. is polyphyletic partly because Schoepfia is more closely related
to Misodendrum and Loranthaceae than to Olacaceae s. str. Although
Olacaceae s. str. is sister to the remaining members of the order,
relationships among the remaining families are not well resolved. Past
molecular studies suggest five independent origins of aerial
parasitism, however, which group first evolved this habit was not
clear. To resolve relationships among the non-Olacaceous families, we
generated sequences from five genes: nuclear SSU and LSU rDNA, and
chloroplast rbcL, matK, and trnL-F. Sequences from 25 taxa representing
all families in the order were used (including four Olacaceae as the
outgroups). Separate and combined data partitions were analyzed with
maximum parsimony and Bayesian inference. All partitions were generally
congruent, thus the total evidence tree will be described. Two major
clades were resolved: 1) Opiliaceae, Santalaceae and Viscaceae which
was sister to 2) Loranthaceae, Misodendraceae and Schoepfiaceae. The
latter family, sister to Misodendraceae, contained Quinchamalium and
Arjona, previously considered members of Santalaceae. The common
ancestor of Misodendrum and Schoepfiaceae was a root parasite, thus
aerial parasitism arose subsequent to the divergence of Misodendrum
which only parasitizes Nothofagus. From a time calibrated Santalales
tree, we estimate that this divergence occurred ca. 75 mybp which
preceeds the evolution of aerial parasitism in Loranthaceae (ca. 40
mybp) and is not incompatible with the fossil history of
Nothofagus. Misodendrum has no tendency towards root parasitism
and is highly adapted to the aerial parasitic habit. Its wind-dispersed
seeds likely represent the earliest adaptation to stem parasitism, i.e.
earlier than Loranthaceae with bird dispersed seeds.
Link to Abstract on BSA website
Lennoaceae (1)
Zhang, Yan, McNeal, Joel R., Smith, Alan R., Kuehl, Jennifer V., Boore, Jeffrey L., dePamphilis, Claude W. Striking
convergence of plastid genomes in independent nonphotosynthetic
lineages. Parasitic plants are valuable models for studying gene
and genome evolution in the absence of photosynthesis. Under relaxed
functional constraints, the plastid genomes of some parasitic plant
have experienced great reductions in gene content and accelerated rates
of evolution for the remaining genes. For example, the fully sequenced
plastid genome of Epifagus virginiana (Orobanchaceae) displays extreme
genome reduction; it lacks functional copies of all photosynthetic and
ndh genes, all four RNA polymerase genes, almost half of the tRNAs, and
one third of the ribosomal protein genes. Accelerated evolution is
observed in Epifagus, a result of both relaxed selection and an
increase in the neutral rate of base substitution. To understand
whether genome evolution is similar in independent lineages of
nonphotosynthetic plants, the plastid genome of the holoparasite
Pholisma arenarium (Lennoaceae/Boraginaceae) was cloned into fosmid
vectors, sequenced, and analyzed. The plastid genome of Pholisma shows
a pattern of gene loss that is strikingly similar to that observed in
Epifagus. All of the photosynthetic genes (with the notable exception
of rbcL) and ndh genes are lost, as are the RNA polymerase genes and
some components of the translation apparatus. The gene losses in
Pholisma are a perfect subset of those observed in Epifagus, and the
remaining genes are also evolving at an accelerated rate. The results
indicate parallel and convergent evolution of the two independent
lineages of nonphotosynthetic plants and also suggest that
photosynthesis has been lost more recently in the lineage including
Pholisma.
Link to Abstract on BSA website
Convolvulaceae (Cuscuta) (2)
McNeal, Joel R., Kuehl, Jennifer V., Boore, Jeffrey L., dePamphilis, Claude W.
Evolution of matK, a conserved plastid intron maturase, in the
parasitic plant genus Cuscuta. Plastid genome content and arrangement
are highly conserved across most land plants and their closest
relatives in the algal order Charales. Almost all plastid introns
appeared prior to the divergence of these two lineages; one such intron
within the transfer RNA trnK-UUU contains a large open reading frame
that encodes a presumed intron maturase, matK. Although this gene is
found in all published land plant and Charophyte plastid genomes,
including that of the nonphotosynthetic angiosperm Epifagus virginiana
(Orobanchaceae), its exact function is still not fully known. The
parasitic angiosperm genus Cuscuta (Convolvulaceae) is highly
heterogeneous in plastid intron content and serves as a good candidate
for studying the intron-splicing function and specificity of matK. We
examined intron evolution and distribution in Cuscuta along with
corresponding evolutionary changes in matK. Loss of many group II
introns from the plastid genome results in substantial change in
selective pressure within the hypothetical RNA-binding region (domain
X) of matK in both Cuscuta and Epifagus. The intron-splicing function
of matK is likely limited to group IIA introns in Cuscuta,
corroborating previous circumstantial evidence from cereal crops.
Link to Abstract on BSA website
Stefanovic, Sasa, Kuzmina, Maria, Costea, Mihai. Delimitation
and relationships of major lineages within Cuscuta subgenus Grammica
(dodders; Convolvulaceae). Subgenera Monogyna, Cuscuta, and
Grammica are recognized traditionally within the parasitic genus
Cuscuta based primarily on the morphology of styles and stigmas. The
largest and most diverse group, subgenus Grammica, comprises some
120-130 species (approximately _ of the species-richness within the
genus) and is distributed primarily throughout the New World, with
Mexico and South America as its centers of diversity. While this group
is well characterized morphologically by two styles with globular
stigmas, neither its monophyly nor the relationships within Grammica
were subjected to a broad and explicit phylogenetic study. In order to
circumscribe the subgenus and assess the relationships among its major
lineages, we conducted the first phylogenetic study of Grammica using
plastid and nuclear sequence data (trnLF and ITS) from a wide taxonomic
sampling covering its morphological, physiological, and geographical
diversity. The results indicate the presence of 15 well-supported
clades. Some of those clades correspond to a large degree to earlier
taxonomic treatments (e.g., subsections sensu Yuncker), but majority of
the groups are identified in this study for the first time. The
backbone relationship among these clades, however, remains unresolved
in many cases. Morphological, taxonomical, and biogeographical
implications of these results are discussed. Also, a minimum of three
potential cases of species of hybrid origin were confirmed or newly
documented from strongly conflicting nuclear and plastid gene trees.
Link to Abstract on BSA website
Orobanchaceae (4)
Morawetz, Jeffery J., Wolfe, Andrea D.
Phylogenetic analyses of the primarily hemiparasitic Alectra
(Orobanchaceae): a preliminary study. Alectra Benth. (Orobanchaceae) is
a genus of mostly hemiparasitic herbaceous plants, and is comprised of
approximately 30 species distributed primarily throughout southern and
eastern Africa as well as Madagascar. Three species are of particular
interest due to their geographical distributions, A. sessiliflora, A.
aspera, and A. stricta. Alectra sessiliflora is a widespread and
polymorphic species present throughout sub-Saharan Africa into India
and China. Additionally, A. aspera and A. stricta occur in tropical
South America, but the relationship of these species to each other and
the rest of the genus is currently unclear. Two types of parasitism
exist within flowering plants (hemi- and holo-parasitism) and within
Alectra both types are known. A preliminary phylogeny of Alectra is
presented here based on combined ITS, trnT-F and rpl16 sequence data.
This phylogeny provides an opportunity to begin answering several
questions about the evolutionary history of the genus; particularly,
the number of times that holoparasitism has arisen and the
biogeographic patterns of diversification of Alectra both within the
Old World and the events leading to its arrival in the New World. The
implications of the placement of the closely related holoparasitic
genus Aeginetia are also examined.
Link to Abstract on BSA website
Morawetz, Jeffery J., Wolfe, Andrea D. Phenetic
analyses of morphological traits in the Alectra sessiliflora complex
(Orobanchaceae). Alectra (Orobanchaceae) is a genus of primarily
hemiparasitic herbs. Alectra sessiliflora var. sessiliflora, var.
senegalensis, and var. monticola form a morphologically cohesive group
with overlapping distributions throughout sub-Saharan Africa, and are
characterized by sessile yellow flowers and a branching habit.
Traditional characters used to distinguish these varieties were stamen
filament pubescence and calyx pubescence. These characters are variable
and overlapping, thus preventing confident determination of specimens.
This difficulty suggested that the taxonomic delimitations are
problematic, and required further investigation. A phenetic study was
undertaken to determine if this complex is best treated as a single
large polymorphic taxon or as a series of similar yet discrete taxa.
Twenty-four morphological traits were examined on 134 operational
taxonomic units (OTUs) and the data were analyzed using UPGMA and PCoA.
Discrete clusters were not identified by the analyses. These results
suggest that A. sessiliflora should be recognized as a single species
without infraspecific divisions. The implications of this study will be
addressed in a monograph of Alectra currently in preparation.
Link to Abstract on BSA website
McNeal, Joel R., Bennett, Jonathan R., Wolfe, Andrea D., Mathews,
Sarah. Five-gene phylogeny of Orobanchaceae (Broomrape Family). The
family Orobanchaceae is nearly cosmopolitan in distribution and
contains the most agriculturally damaging parasitic weeds in the world.
We have gathered DNA sequence data from more than 50 genera and 170
species of Orobanchaceae using both nuclear (ribosomal internal
transcribed spacer, phytochrome A, and phytochrome B) and plastid
(ribosomal protein subunit 2 and maturase K) loci in order to ascertain
phylogenetic relationships within the family. We have greatly augmented
taxon sampling for genes previously used for Orobanchaceae
phylogenetics, and novel phyB data corroborates published phylogenies
from the other individual loci. The combined five-gene dataset
represents the highest degree of taxonomic sampling within this
economically important family to date and provides greater phylogenetic
resolution than the single-gene phylogenies.
Link to Abstract on BSA website
Tsai, Yi-Hsin Erica, Manos, Paul S.
Do hosts and their obligate parasites co-migrate? Inferences from
post-glacial phylogeographies of beech (Fagus grandifolia) and
beech-drop (Epifagus virginiana). Describing how the migration patterns
of parasites are constrained by their hosts is a first step in
understanding the cohesiveness of communities during migration. This
study compares the post-glacial migration of the parasitic plant,
Epifagus virginiana (beechdrop; Orobanchaceae), with the migration
history of its host tree, Fagus grandifolia (American beech; Fagaceae).
The host's post-glacial history is well known with past molecular work
describing its range expansion and paleo-pollen data reflecting
population density changes over time. This history is used to frame
questions regarding the migration of the obligate, host-specific
parasite, E. virginiana; for instance, was E. virginiana present at the
migration front of F. grandifolia with its range expansion mimicking
its host's, or was the parasite's spread limited by host density with
its migration matching the host's population density changes? To
discern among these scenarios we present the molecular phylogeography
of E. virginiana based on chloroplast DNA sequences. We identify the
parasite's glacial refugia, migration corridors, and overall population
structure and compare these with the host’s history. The results
show that the range expansion of E. virginiana is largely coincident
with the density changes of its host, though in some instances E.
virginiana was present in the low density host populations at the
migration front. The dependence of parasite establishment on host
density results in a lag time between expansion into an area by the
host and colonization by the parasite. How the host's distribution and
density dictates the parasite's movements has implications for the
migration capacity of E. virginiana and how quickly it can respond to
climate change. Also, this study provides significant data on
herbaceous plant migration that is currently missing and can answer
broader questions about the cohesiveness of communities during
migration.
Link to Abstract on BSA website
SIUC / College of Science / Parasitic Plant Connection
URL: http://www.parasiticplants.siu.edu/meetings/Bot2006ParAbstracts.html
Last updated: 25-Sept-06 / dln