Molecular dialogue between host and parasitic plants

02 August 2021 Dept. of Plant Biotechnology 1

Molecular Dialog Between
Parasitic Plants and
Their Hosts
Upasana Mohapatra
PALB-8092
II Ph. D. Plant Biotechnology
UAS, GKVK, Bengaluru

CONTENTS
Introduction
Parasite identification of hosts
Parasite–host exchange of RNAs
Host Reaction to Attack by Root Parasitic Plants
Casestudies
Summary
Future prospectiveses

INTRODUCTION
• Parasitism is a highly successful life strategy and a theme that bridges all
kingdoms of life
• Parasitic plant: plant that receives all or part of its nutrients through a
haustorial connection to another plant.
Hemiparasite:
Parasitic plant that can
photosynthesize and thus is not
completely dependent on the host
plant for sugars
Holoparasite:
Parasitic plant that lacks the capacity for
photosynthesis and thus relies entirely
on uptake of sugars from host plants
Facultative parasite:
a parasitic plant that can complete its
lifecycle as an autotrophic plant but
retains the capacity to
opportunistically parasitize host
plants. Facultative parasitic plants
must be hemiparasitic
Obligate parasites
Must parasitize a host in order to
complete their life cycles. Seeds of some
obligate parasites require exposure to
host signal molecules in order to
germinate
Clarke et al., 2019

Clarke et al., 2019

• In angiosperms, parasitism has independently evolved
at least 12 or 13 times, and by recent estimates
approximately 1% of angiosperm species are
parasitic.
Clarke et al., 2019

PARASITE IDENTIFICATION OF HOSTS
Germination
• Strigolactones (SLs) are the best-characterized class of germination stimulants
• At least 20 different SL molecules have been identified in plants and plant families
produce varying forms such that parasite seeds are able to differentiate among
hosts on the basis of the identity of exuded SLs.
Clarke et al., 2019

Parasitic plants use a protein related to D14
termed KARRIKIN INSENSITIVE 2 (KAI2;
also known as HYPOSENSITIVE TO
LIGHT)
The KAI2 genes in parasitic
Orobanchaceae
diverged KAI2
(provides parasites with a
mechanism)
to
1. Recognize specific host SLs,
2. Adapt to changes in host SL
profiles,
3. Shift to recognize new hosts
expansion and
specialization

Clarke et al., 2019

Locating the Host
• Chemotropic growth of the parasite radicle in Orobanchaceae
has been postulated for years

Yoshida & Shirasu, 2009

.

Runyon et al., 2016

THE HAUSTORIUM AND ITS
DEVELOPMENT
• Haustoria are parasite-encoded multifunctional organs that attach the
parasite to the host, penetrate into host tissues, and ultimately establish the
physiological conduit through which resources flow between parasite and
host
Lateral haustoria
• Develop on the sides of roots or stems,
and terminal haustoria
• More common cuscuta and most
orobanchaceae
• Develop on functioning roots without
• Altering the tip meristem so multiple
haustoria can develop on a single root
Terminal haustoria
• Develop on the tips of newly emerging
radicles
• More specialized
• Obligate parasites
• Alter the tip meristem so no additional
root growth occurs until the haustorium
has
• Successfully invaded the host.

Haustoria-inducing factors
(HIFs):
chemical cues released by host
plants stimulating production of
haustorial connections in parasitic
plants
Five general classes
Flavonoids,
Phenolic Acids,
Quinones,
Cytokinins
Cyclohexene Oxides
First HIF identified
Clarke et al., 2019

• Phenolic acids become active HIFs only after oxidization to
their sister quinones, haustorium induction may depend on the
redox state of the inducer.
• Subsequent experiments indicated that semiquinone
intermediates formed during redox cycling between quinone
and hydroquinone states of the HIF initiate a redox-sensitive
signaling pathway leading to haustorium development
Clarke et al., 2019

Not all Orobanchaceae respond to the same
HIFs
T. versicolor forms haustoria
in response to DMBQ, but
Triphysaria eriantha does not
• Orobanche and Phelipanche do not form obvious haustorial structures in
response to DMBQ
• They form haustoria when treated with root exudates of Brassica napus
Clarke et al., 2019

Attachment via Haustorial Hairs
The first contact between certain Orobanchaceae parasites and hosts is made by haustorial
hairs, which cement the parasite to the host
When host and parasite roots were forced to grow closely together, haustorial hair mutants
produced similar numbers of haustoria as do wild-type P. japonicum.
Thus, haustorial hairs may play a role in host–parasite associations but not in haustorium
initiation
Clarke et al., 2019

Hormone action
• As growth regulators of plant organogenesis, hormones play
multiple roles in the development of haustoria. Major
hormones are
• Auxin
• Ethylene
• Cytokinin
Clarke et al., 2019

Hormone action in haustoria development
• Major hormones are
• Auxin,
• Ethylene
• Cytokinin
2005

CONTROL
pHG8 YUC3-1

Viscum album on crabapple tree Malus toringoides

PARASITE–HOST EXCHANGE OF RNAs
• Parasites exchange with their hosts’ proteins and RNAs that
could contribute to shaping interactions between species.
• A large number of C. campestris microRNAs are strongly
expressed specifically at haustorial junctions.
• Functional RNA-interference signals also move across parasitic plant haustoria.
• Hairpin transgenes in host plants trigger effective RNA interference in both T.
versicolor and C. pentagona
• This host-induced gene silencing can be used to target parasite genes critical for
parasite growth and is therefore a potential strategy for crop improvement.
Clarke et al., 2019

Pre-attachment resistance includes all
(a) no or reduced production of
germination stimulant(s);
(b) production of germination
inhibitors;
(c) delay, reduction, or complete
inhibition of haustorium formation
leading to attachment incompetence;
and
(d) development of
preformed mechanical or structural
barriers on the host surface to impede
attachment.
(a) abiosis, the synthesis and release of
cytotoxic compounds (e.g., phenolic acids,
phytoalexins), by the challenged host root
cells;
(b) rapid formation of physical barriers to
prevent possible pathogen ingress and growth
(e.g., lignification and other forms of cell wall
modification at the host–parasite interface;
(c) Release of reactive oxygen species and
activation of programmed cell death in the
form of a hypersensitive response at the point
of parasite attachment to limit parasite
development and retard its penetration;
(d) prevention of the parasite establishing the
essential functional vascular continuity
(i.e., xylem-to-xylem and/or phloem-to-phloem
connections) with the host, delaying parasite
growth followed by parasite developmental
arrest and eventual death
Host Reaction to Attack by Root
Parasitic Plants
Gressel et al., 2013

the haustorium is well developed with xylem
continuity between parasite and host;
in the resistant interaction, the haustorium
invades the host root cortex but is not able to
penetrate the endodermis to establish host–
parasite xylem connectivity
lignification of
host tissue around the invading parasite
the haustorium penetrates into the
cortex but does not form connections with the
host xylem
An unsuccessful O. crenata penetration in
root of a resistant vetch cultivar 20 days after
inoculation, showing lignification of host
cells, accumulation of a brown secreted
material
root showing a xylem vessel filled with
mucilage 30 days after inoculation with O.
crenata
Gressel et al., 2013

Parasitic plant and host interaction
Clarke et al., 2019

Variable parasite growth form and mortality when grown with different hosts, suggest a
dynamic and host-dependent molecular dialogue between the parasite and host

Host specificity and how it may restrict the distribution of hemi-parasitic plants in different
plant communities along a steep ecological gradient.

1. Phytohormone quantification, transcriptomic analysis and bioassays were
performed to determine the responses of Cuscuta australis and its soybean
(Glycine max) hosts to the feeding of green peach aphid (GPA; Myzus persicae) on
C. australis.
2. Investigated whether GPA feeding on Cuscuta induces local defense responses in
the attacked Cuscuta plants,
3. Whethrer Cuscuta sends systemic signals to the hosts, and if the systemic signals
can elevate the resistance of hosts to subsequent insect attack.
Case study 1

Materials and Methods
Plants –grown in glass house
insects – collected from a
brassicaceous plant 10 cm
GPA-infested C. australis effects on the transcriptomic and phytohormonal responses of its
soybean host was studied
Extraction and quantification of phytohormones
RNA-seq and data analysis
RT-qPCR
GPA-infested C. australis effect on the insect resistance of its soybean host
Detection of volatile-induced systemic responses in soybean plants
Insect-infested soybean effect on GPA resistance of C. australis

Cuscuta + Aphids Cuscuta - Aphids
Soybean Soybean
Treated Control
Soybean
aphids
Soybean
aphids

Conclusion
• Decreased salicylic acid levels and 172 differentially expressed genes
(DEGs) were found in GPA-attacked C. australis, and the soybean hosts
exhibited increased jasmonic acid contents and 1015 DEGs, including >
100 transcription factor genes.
• Importantly, GPA feeding on C. australis increased the resistance of the
soybean host resulting in 21% decreased leafworm mass and 41%
reduced aphid survival rate.
• GPA herbivory-induced systemic signal from C. australis can elicit a strong
transcriptomic reconfiguration in the soybean host.

Cas9/single guide (sg) RNA constructs were targeted to the second exon of CCD8 in tomato
(Solanum lycopersicum L.) plants. Several CCD8Cas9 mutated tomato lines with variable
insertions or deletions in CCD8 were obtained with no identified off-targets
• Compared to control tomato plants, the CCD8Cas9 mutant had morphological changes
that included dwarfing, excessive shoot branching and adventitious root formation.
• In addition, SL-deficient CCD8Cas9 mutants showed a significant reduction in parasite
infestation compared to non-mutated tomato plants
Case study 2

Material and method
CCD8sgRNA design and plasmid construction.
Mutant verification and genotyping
Analysis of off-target mutations.
Evaluation of P. aegyptiaca resistance assay
SL extraction and analysis using LC-MS/MS
RNA isolation and quantitative real-time PCR.
Carotenoid extract analysis.

Conclusion
• Mutations in CCD8 can negatively affect tomato plant morphology;
in a rootstock grafted to a wild-type scion, and might be combined
with tomato rootstocks that are already resistant to fungal pathogens, viruses,
and nematodes.
• This method is expected to be effective against other Phelipanche and
Orobanche species, if the parasite species share sufficient homology in
their target sequences.
• In addition, the mutated plants are devoid of foreign DNA sequences and
are not considered genetically modified organisms

Summary
• Development of the haustorium and its interactions with the
host plant are becoming exciting areas of research, and new
insights have emerged into its role in the exchange of
hormones, nutrients, and macromolecules, including RNAs.
• Transfer of mRNA and microRNA between host and parasite
appears to be an important virulence and host adaptation
strategy in Cuscuta.
• Parallels are emerging between the molecular mechanisms
mediating parasitic plant–host interactions and other plant–
pathogen interactions, including the elicitation of host innate
immunity.

Future prospectives
1. The processes by which germination factors and haustoria-inducing factors (HIFs) are
secreted from host roots as well as their fate in the microbial-rich rhizosphere need to be
better understood.
2. To clarify the importance of this novel virulence and adaptation strategy, researchers need to
determine whether the transfer of microRNA and mRNA enhances parasite.
3. It is important to determine which damage- and parasite-associated molecular patterns as well
as other elicitors of host plant immunity are present during host–parasite interactions and
during which stages of parasitism the elicitors are present.
4. The presence and function of putative parasitic plant effector proteins should be studied
across a wide range of parasitic plants to elucidate their host targets and the pathways they
disrupt.
5. A critical issue—as yet unrealized—is to translate our gains in fundamental knowledge of
parasitism toward deployment of effective parasitic weed control strategies

References
• BARI, V.K., NASSAR, J.A., KHEREDIN, S.M., GAL-ON, A., RON, M., BRITT, A., STEELE, D., YODER, J. AND ALY,
R., 2019. CRISPR/Cas9-mediated mutagenesis of CAROTENOID CLEAVAGE DIOXYGENASE 8 in tomato provides
resistance against the parasitic weed Phelipanche aegyptiaca. Scientific reports, 9(1):1-12.
• CLARKE, C.R., TIMKO, M.P., YODER, J.I., AXTELL, M.J. AND WESTWOOD, J.H., 2019. Molecular Dialog Between
Parasitic Plants and Their Hosts. Annual review of phytopathology, 57:279-299.
• GRESSEL, J., MUSSELMAN, L.J. AND JOEL, D.M. eds., 2013. Parasitic Orobanchaceae: Parasitic Mechanisms and
Control Strategies. Springer Berlin Heidelberg.
• HETTENHAUSEN, C., LI, J., ZHUANG, H., SUN, H., XU, Y., QI, J., ZHANG, J., LEI, Y., QIN, Y., SUN, G. AND WANG,
L., 2017. Stem parasitic plant Cuscuta australis (dodder) transfers herbivory-induced signals among plants. Proceedings of
the National Academy of Sciences, 114(32):6703-6709.
• HONAAS, L.A., JONES, S., FARRELL, N., KAMEROW, W., ZHANG, H., VESCIO, K., ALTMAN, N.S., YODER, J.I.
AND DEPAMPHILIS, C.W., 2019. Risk versus reward: host dependent parasite mortality rates and phenotypes in the
facultative generalist Triphysaria versicolor. BMC plant biology, 19(1):334.
• RUNYON, J.B., MESCHER, M.C. AND DEMORAES, C.M., 2006. Volatile chemical cues guide host location and host
selection by parasitic plants. Science, 313 (5795): 1964-1967.
• SPALLEK, T., MELNYK, C.W., WAKATAKE, T., ZHANG, J., SAKAMOTO, Y., KIBA, T., YOSHIDA, S., MATSUNAGA,
S., SAKAKIBARA, H. AND SHIRASU, K., 2017. Interspecies hormonal control of host root morphology by parasitic
plants. Proceedings of the National Academy of Sciences, 114(20):5283-5288.
• TOMILOV, A.A., TOMILOVA, N.B., ABDALLAH, I. AND YODER, J.I., 2005. Localized hormone fluxes and early
haustorium development in the hemiparasitic plant Triphysaria versicolor. Plant Physiology, 138(3):1469-1480.
• ZHUANG, H., LI, J., SONG, J., HETTENHAUSEN, C., SCHUMAN, M.C., SUN, G., ZHANG, C., LI, J., SONG, D. AND
WU, J., 2018. Aphid (Myzus persicae) feeding on the parasitic plant dodder (Cuscuta australis) activates defense responses in
both the parasite and soybean host. New Phytologist, 218(4):1586-1596.

Molecular dialogue between host and parasitic plants

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Molecular dialogue between host and parasitic plants

Similar to Molecular dialogue between host and parasitic plants (20)

More from Upasana Mohapatra

More from Upasana Mohapatra (8)

Recently uploaded

Recently uploaded (20)

Molecular dialogue between host and parasitic plants