<Emphasis Type="Italic">Agrobacterium rhizogenes</Emphasis> transformed calli of the holoparasitic plant <Emphasis Type="Italic">Phelipanche ramosa</Emphasis> maintain parasitic competence

Phelipanche and Orobanche spp. (broomrapes) are economically important parasitic weeds, causing severe damage to many agricultural crops. However, conventional methods to control these parasitic weeds are often not effective. Targeting molecular and biochemical processes involved in the establishment of the connection between the parasite and the host may offer a new perspective for control. However, progress in the understanding of these processes is hampered by the fact that genetic transformation and regeneration of these parasites is difficult if not impossible due to their specific lifecycle. Phelipanche and Orobanche spp. are holoparasites that need to attach to the roots of a host plant to get their assimilates, nutrients and water to develop and reproduce. The present study describes a highly efficient genetic transformation and regeneration protocol for the root holoparasitic Phelipanche ramosa. We present a new transformation system for P. ramosa using Agrobacterium rhizogenes MSU440 carrying a non-destructive selection marker gene coding for a red fluorescent protein (DsRed1). Using this protocol up to 90% transformation efficiency was obtained. We transformed 4 weeks old P. ramosa calli and transgenic calli expressing DsRed1 were then cultured on host plants. For the first time, we present shoot and flower development of the transgenic parasitic plant P. ramosa after successful connection of transgenic calli with the host plant roots. Moreover, we also present, for the first time, growth and development of P. ramosa shoots and flowers in vitro in the absence of a host plant.     

Notch1 binds and induces degradation of Snail in hepatocellular carcinoma

Background

Infection processes consist of a sequence of steps, each critical for the interaction between host and parasite. Studies of host-parasite interactions rarely take into account the fact that different steps might be influenced by different factors and might, therefore, make different contributions to shaping coevolution. We designed a new method using the Daphnia magna - Pasteuria ramosa system, one of the rare examples where coevolution has been documented, in order to resolve the steps of the infection and analyse the factors that influence each of them.

Results

Using the transparent Daphnia hosts and fluorescently-labelled spores of the bacterium P. ramosa, we identified a sequence of infection steps: encounter between parasite and host; activation of parasite dormant spores; attachment of spores to the host; and parasite proliferation inside the host. The chances of encounter had been shown to depend on host genotype and environment. We tested the role of genetic and environmental factors in the newly described activation and attachment steps. Hosts of different genotypes, gender and species were all able to activate endospores of all parasite clones tested in different environments; suggesting that the activation cue is phylogenetically conserved. We next established that parasite attachment occurs onto the host oesophagus independently of host species, gender and environmental conditions. In contrast to spore activation, attachment depended strongly on the combination of host and parasite genotypes.

Conclusions

Our results show that different steps are influenced by different factors. Host-type-independent spore activation suggests that this step can be ruled out as a major factor in Daphnia - Pasteuria coevolution. On the other hand, we show that the attachment step is crucial for the pronounced genetic specificities of this system. We suggest that this one step can explain host population structure and could be a key force behind coevolutionary cycles. We discuss how different steps can explain different aspects of the coevolutionary dynamics of the system: the properties of the attachment step, explaining the rapid evolution of infectivity and the properties of later parasite proliferation explaining the evolution of virulence. Our study underlines the importance of resolving the infection process in order to better understand host-parasite interactions.     

Specific developmental pathways underlie host specificity in the parasitic plant Orobanche

Parasitic angiosperms are an ecologically and economically important group of plants. However our understanding of the basis for host specificity in these plants is embryonic. Recently we investigated host specificity in the parasitic angiosperm Orobanche minor, and demonstrated that this host generalist parasite comprises genetically defined races that are physiologically adapted to specific hosts. Populations occurring naturally on red clover (Trifolium pratense) and sea carrot (Daucus carota subsp. gummifer) respectively, showed distinct patterns of host specificity at various developmental stages, and a higher fitness on their natural hosts, suggesting these races are locally adapted. Here we discuss the implications of our findings from a broader perspective. We suggest that differences in signal responsiveness and perception by the parasite, as well as qualitative differences in signal production by the host, may elicit host specificity in this parasitic plant. Together with our earlier demonstration that these O. minor races are genetically distinct based on molecular markers, our recent data provide a snapshot of speciation in action, driven by host specificity. Indeed, host specificity may be an underestimated catalyst for speciation in parasitic plants generally. We propose that identifying host specific races using physiological techniques will complement conventional molecular marker-based approaches to provide a framework for delineating evolutionary relationships among cryptic host-specific parasitic plants.Key words: host specificity, parasitic plant, broomrape, orobanche, speciation     

What are the traits of Phelipanche ramosa (L.) Pomel that contribute to the success of its biological cycle on its host Brassica napus L.?

In France, the fact that the holoparasitic plant Phelipanche ramosa has adapted to oilseed rape over the past two decades is deeply worrying, as it can cause over 80% yield losses. Its distribution area and the range of its host plants, whether they are cultivated plants or weeds, are expanding dramatically. As no natural regression of the infestation has been recorded so far, we undertook a detailed study of the different steps of the biological cycle of the P. ramosa/oilseed rape pathosystem to determine the adaptive traits that favour the parasite's success. We combined experimental approaches involving controlled conditions with in vitro and in pot co-cultivation on the one hand and a field trial on the other hand. These experiments allowed us to determine a 4-mm zone around host roots within which oilseed rape root exudates stimulate the germination of P. ramosa, the early action of host root exudates and the rapid fixation of the parasite on host roots. We also unveiled that P. ramosa was able to tune its biological cycle to that of oilseed rape. The important trophic relationships between the parasite and its host induced phenotypic (dwarfism, leaf chlorosis, silique abortion) as well as agronomical (90% yield losses) consequences on oilseed rape. Our results can constitute a relevant basis for further experimental studies. The research perspectives they open will focus on key-processes of the host–parasite relationship, and more particularly on the trophic relationships that are set up as far as carbon assimilates and minerals such as nitrogen are concerned.     

Dose effects and density-dependent regulation of two microparasites of<Emphasis Type="Italic"> Daphnia magna</Emphasis>

Individual hosts constitute a limited resource for parasites, suggesting that density-dependent effects may play a role in within-host growth and parasite regulation. This hypothesis has been tested for several helminth parasites, but not for microparasites. We therefore examined dose-response patterns for the microparasitic bacterium Pasteuria ramosa and the fungus Metschnikowiella biscuspidata infecting the planktonic crustacean Daphnia magna. With increasing numbers of transmission stages administered to the host we found that host fecundity and survival and parasite transmission-stage production declined. Using a k-value analysis, a method that quantifies the strength of density dependence, we found for both parasites that density dependence acted at all doses, indicating the absence of a minimum density below which parasite fitness is density- independent. At low doses density was exactly compensated, but it was overcompensated at high doses. Overcompensation at high doses was weak for P. ramosa, but high for M. biscuspidata. At the two highest doses M. biscuspidata killed its hosts before any transmission stages were produced. Our data indicate that density dependence is expressed through retarded spore development in P. ramosa, but through both host mortality and reduced parasite fecundity in M. biscuspidata. A further experiment (P. ramosa only) revealed that in well-fed hosts more parasite transmission stages are produced than in poorly fed hosts, suggesting that competition for host resources retards P. ramosa development. Our data for P. ramosa, but not for M. biscuspidata, are largely consistent with assumptions made in models on microparasite epidemiology. We draw attention to the relevance of dose effects and within-host competition for the evolution of virulence. Received: 15 July 1999 / Accepted: 14 September 1999     

Apoplastic Venom Allergen-like Proteins of Cyst Nematodes Modulate the Activation of Basal Plant Innate Immunity by Cell Surface Receptors

Despite causing considerable damage to host tissue during the onset of parasitism, nematodes establish remarkably persistent infections in both animals and plants. It is thought that an elaborate repertoire of effector proteins in nematode secretions suppresses damage-triggered immune responses of the host. However, the nature and mode of action of most immunomodulatory compounds in nematode secretions are not well understood. Here, we show that venom allergen-like proteins of plant-parasitic nematodes selectively suppress host immunity mediated by surface-localized immune receptors. Venom allergen-like proteins are uniquely conserved in secretions of all animal- and plant-parasitic nematodes studied to date, but their role during the onset of parasitism has thus far remained elusive. Knocking-down the expression of the venom allergen-like protein Gr-VAP1 severely hampered the infectivity of the potato cyst nematode Globodera rostochiensis. By contrast, heterologous expression of Gr-VAP1 and two other venom allergen-like proteins from the beet cyst nematode Heterodera schachtii in plants resulted in the loss of basal immunity to multiple unrelated pathogens. The modulation of basal immunity by ectopic venom allergen-like proteins in Arabidopsis thaliana involved extracellular protease-based host defenses and non-photochemical quenching in chloroplasts. Non-photochemical quenching regulates the initiation of the defense-related programmed cell death, the onset of which was commonly suppressed by venom allergen-like proteins from G. rostochiensis, H. schachtii, and the root-knot nematode Meloidogyne incognita. Surprisingly, these venom allergen-like proteins only affected the programmed cell death mediated by surface-localized immune receptors. Furthermore, the delivery of venom allergen-like proteins into host tissue coincides with the enzymatic breakdown of plant cell walls by migratory nematodes. We, therefore, conclude that parasitic nematodes most likely utilize venom allergen-like proteins to suppress the activation of defenses by immunogenic breakdown products in damaged host tissue.     

The polypeptide components of the parasporal fibres of Pasteuria penetrans

A variety of treatments were tested for their ability to solubilize the parasporal fibres from Pasteuria penetrans, a parasite of some plant–parasitic nematodes. Selective solubilization of the parasporal fibres resulted from some of the extraction procedures tested. Subsequent acrylamide gel electrophoresis and Western blotting of the resolved polypeptides, using polyclonal sera against the spores, disclosed up to 15 distinct bands, ranging in size from 12 to 195 kDa. An N-terminal amino acid sequence was obtained from a 50 kDa polypeptide and an oligonucleotide primer deduced from it. A whole cell, fluorescent, primed in situ labelling (PRINS) technique was adapted to be applicable to spores of P. penetrans and P. ramosa, a parasite of water fleas. Positive responses were obtained using the parasporal fibre primer on spores of the former but not of the latter organism, implying that this 50 kDa polypeptide is produced by P. penetrans but not by P. ramosa.     

CROSS‐SPECIES INFECTION TRIALS REVEAL CRYPTIC PARASITE VARIETIES AND A PUTATIVE POLYMORPHISM SHARED AMONG HOST SPECIES

A parasite's host range can have important consequences for ecological and evolutionary processes but can be difficult to infer. Successful infection depends on the outcome of multiple steps and only some steps of the infection process may be critical in determining a parasites host range. To test this hypothesis, we investigated the host range of the bacterium Pasteuria ramosa, a Daphnia parasite, and determined the parasites success in different stages of the infection process. Multiple genotypes of Daphnia pulex, Daphnia longispina and Daphnia magna were tested with four Pasteuria genotypes using infection trials and an assay that determines the ability of the parasite to attach to the hosts esophagus. We find that attachment is not specific to host species but is specific to host genotype. This may suggest that alleles on the locus controlling attachment are shared among different host species that diverged 100 million year. However, in our trials, Pasteuria was never able to reproduce in nonnative host species, suggesting that Pasteuria infecting different host species are different varieties, each with a narrow host range. Our approach highlights the explanatory power of dissecting the steps of the infection process and resolves potentially conflicting reports on parasite host ranges.     

The expression of virulence during double infections by different parasites with conflicting host exploitation and transmission strategies

In many natural populations, hosts are found to be infected by more than one parasite species. When these parasites have different host exploitation strategies and transmission modes, a conflict among them may arise. Such a conflict may reduce the success of both parasites, but could work to the benefit of the host. For example, the less‐virulent parasite may protect the host against the more‐virulent competitor. We examine this conflict using the waterflea Daphnia magna and two of its sympatric parasites: the blood‐infecting bacterium Pasteuria ramosa that transmits horizontally and the intracellular microsporidium Octosporea bayeri that can concurrently transmit horizontally and vertically after infecting ovaries and fat tissues of the host. We quantified host and parasite fitness after exposing Daphnia to one or both parasites, both simultaneously and sequentially. Under conditions of strict horizontal transmission, Pasteuria competitively excluded Octosporea in both simultaneous and sequential double infections, regardless of the order of exposure. Host lifespan, host reproduction and parasite spore production in double infections resembled those of single infection by Pasteuria. When hosts became first vertically (transovarilly) infected with O. bayeri, Octosporea was able to withstand competition with P. ramosa to some degree, but both parasites produced less transmission stages than they did in single infections. At the same time, the host suffered from reduced fecundity and longevity. Our study demonstrates that even when competing parasite species utilize different host tissues to proliferate, double infections lead to the expression of higher virulence and ultimately may select for higher virulence. Furthermore, we found no evidence that the less‐virulent and vertically transmitting O. bayeri protects its host against the highly virulent P. ramosa.     

A novel approach to parasite population genetics: Experimental infection reveals geographic differentiation,recombination and host‐mediated population structure in Pasteuria ramosa,a bacterial parasite of Daphnia

The population structure of parasites is central to the ecology and evolution of host‐parasite systems. Here, we investigate the population genetics of Pasteuria ramosa, a bacterial parasite of Daphnia. We used natural P. ramosa spore banks from the sediments of two geographically well‐separated ponds to experimentally infect a panel of Daphnia magna host clones whose resistance phenotypes were previously known. In this way, we were able to assess the population structure of P. ramosa based on geography, host resistance phenotype and host genotype. Overall, genetic diversity of P. ramosa was high, and nearly all infected D. magna hosted more than one parasite haplotype. On the basis of the observation of recombinant haplotypes and relatively low levels of linkage disequilibrium, we conclude that P. ramosa engages in substantial recombination. Isolates were strongly differentiated by pond, indicating that gene flow is spatially restricted. Pasteuria ramosa isolates within one pond were segregated completely based on the resistance phenotype of the host—a result that, to our knowledge, has not been previously reported for a nonhuman parasite. To assess the comparability of experimental infections with natural P. ramosa isolates, we examined the population structure of naturally infected D. magna native to one of the two source ponds. We found that experimental and natural infections of the same host resistance phenotype from the same source pond were indistinguishable, indicating that experimental infections provide a means to representatively sample the diversity of P. ramosa while reducing the sampling bias often associated with studies of parasite epidemics. These results expand our knowledge of this model parasite, provide important context for the large existing body of research on this system and will guide the design of future studies of this host‐parasite system.     

Within- and between-population variation for resistance of Daphnia magna to the bacterial endoparasite Pasteuria ramosa

Genetic variation among hosts for resistance to parasites is an important assumption underlying evolutionary theory of host and parasite evolution. Using the castrating bacterial parasite Pasteuria ramosa and its cladoceran host Daphnia magna, we examined both within- and between-population genetic variation for resistance. First, we tested hosts from four populations for genetic variation for resistance to three parasite isolates. Allozyme analysis revealed significant host population divergence and that genetic distance corresponds to geographic distance. Host and parasite fitness components showed strong genetic differences between parasite isolates for host population by parasite interactions and for clones within populations, whereas host population effects were significant for only a few traits. In a second experiment we tested explicitly for within-population differences in variation for resistance by challenging nine host clones from a single population with four different parasite spore doses. Strong clone and dose effects were evident. More susceptible clones also suffered higher costs once infected. The results indicate that within-population variation for resistance is high relative to between-population variation. We speculate that P. ramosa adapts to individual host clones rather than to its host population.     

Carotenoid inhibitors reduce strigolactone production and Striga hermonthica infection in rice

The strigolactones are internal and rhizosphere signalling molecules in plants that are biosynthesised through carotenoid cleavage. They are secreted by host roots into the rhizosphere where they signal host-presence to the symbiotic arbuscular mycrorrhizal (AM) fungi and the parasitic plants of the Orobanche, Phelipanche and Striga genera. The seeds of these parasitic plants germinate after perceiving these signalling molecules. After attachment to the host root, the parasite negatively affects the host plant by withdrawing water, nutrients and assimilates through a direct connection with the host xylem. In many areas of the world these parasites are a threat to agriculture but so far very limited success has been achieved to minimize losses due to these parasitic weeds. Considering the carotenoid origin of the strigolactones, in the present study we investigated the possibilities to reduce strigolactone production in the roots of plants by blocking carotenoid biosynthesis using carotenoid inhibitors. Hereto the carotenoid inhibitors fluridone, norflurazon, clomazone and amitrole were applied to rice either through irrigation or through foliar spray. Irrigation application of all carotenoid inhibitors and spray application of amitrole significantly decreased strigolactone production, Striga hermonthica germination and Striga infection, also in concentrations too low to affect growth and development of the host plant. Hence, we demonstrate that the application of carotenoid inhibitors to plants can affect S. hermonthica germination and attachment indirectly by reducing the strigolactone concentration in the rhizosphere. This finding is useful for further studies on the relevance of the strigolactones in rhizosphere signalling. Since these inhibitors are available and accessible, they may represent an efficient technology for farmers, including poor subsistence farmers in the African continent, to control these harmful parasitic weeds.     

Recognition of root exudates by seeds of broomrape (Orobanche and Phelipanche) species

Background and Aims

The long co-existence of broomrapes and their hosts within the same environment has culminated in a strong adaptation and effective parasitism. As a first step of specialization in the parasitic process, seed receptors of parasitic plant species vary in their ability to recognize compounds released by their hosts. This work aims to investigate potential patterns for the reception requirements needed to activate germination within Orobanche and Phelipanche species.

Methods

Induction of the germination of seeds of nine Orobanche and Pheliphanche species by root exudates of 41 plant species was studied and subjected to biplot multivariate analysis.

Key Results

A high level of specialization in root exudate recognition was found in Orobanche densiflora, O. gracilis and O. hederae, which germinated almost exclusively in contact with root exudates from the plants they infect in nature. At the opposite extreme, Phelipanche aegyptiaca, P. ramosa and O. minor were highly generalist, germinating when in contact with the root exudates of most plant species. Orobanche crenata, O. cumana and O. foetida showed intermediate behaviour.

Conclusions

A universal germination stimulant for all broomrape species has not being identified to date. The synthetic stimulant GR24 is active against most of the weedy broomrape species, but fails with the non-weedy species tested in this study and with the very recent weedy species O. foetida. In addition, germination behaviour of broomrape species depends on the crop plant tested. Weedy broomrapes with a broad host spectrum respond better to the different exudates released by a wide range of crops and wild species than do non-weedy broomrapes, which have a narrow host spectrum and are more restricted to their host range. Root exudates of many plant species were active in stimulating germination of seeds of Orobanche and Phelipanche species for which they are not described as hosts, representing interesting examples of potential trap crops.Key words: Xenognosis, broomrape, root exudate, germination, Orobanche, Phelipanche     

The role of peptidyl-prolyl cis/trans isomerase genes of Arabidopsis thaliana in plant defense during the course of Xanthomonas campestris infection

Experimental data obtained in this study had shown the involvement of A. thaliana immunophilin genes At2g16600, At4g33060, and At5g48570 in plant defense responses to the Xanthomonas campestris invasion. We had found not only that the expression levels of these genes changed upon bacterial infection, but also that the plant’s resistance to the pathogen was increased if the expression levels of the immunophilin genes were elevated in the host cells.     

Cytokinin treated microcalli of Phelipanche ramosa: an efficient model for studying haustorium formation in holoparasitic plants

The ability of Orobanchaceae to establish a parasitic relationship is based on the development of a specific organ called haustorium. Previous studies in Phelipanche aegyptiaca and P. ramosa have underlined the interest of producing calli from germinated seeds as an efficient genetic transformation system, but they also pointed the need to improve the attachment rate of infectious calli to the host plant as well as the seed yield of the regenerated plants following attachment. It was previously shown that haustorium formation in P. ramosa is triggered by cytokinins. The present work demonstrates that one month-old microcalli produced from germinated seeds displayed a response to c/tZ similar to germinated seeds, as shown by the temporal expression profile of markers genes of cytokinin-related haustorium initiation, including PrRR5, PrCKX2, PrCKX4, PrTRN2 and PrZFP6. In addition, a 48 h treatment of microcalli with c/tZ (10^?7 M) before infestation triggered a 4-fold increase in the attachment rate of microcalli to tomato roots after 18 days in minirhizotrons when compared to untreated microcalli. Finally, it also outlines that increasing the aggressiveness of microcalli with a c/tZ treatment followed by the transfer of parasitized tomato plants into pots significantly improved seed yield of regenerated P. ramosa plants. Indeed, high amounts of viable seeds which germinated at more than 90% in response to GR24 were harvested after a 10 weeks-co-cultivation period. According to these results, cytokinin treated P. ramosa microcalli thus appear to be a good tool for further functional studies in holoparasitic plants, especially on haustorium formation.

     

Genomic regions of pufferfishes responsible for host specificity of a monogenean parasite, Heterobothrium okamotoi

The genetic mechanisms underlying host specificity of parasitic infections are largely unknown. After hatching, the larvae of the monogenean parasite, Heterobothrium okamotoi, attach to the gill filaments of hosts and the post-larval worms develop there by consuming nutrients from the host. The susceptibility to H. okamotoi infection differs markedly among fish species. While this parasite can grow on tiger pufferfish (also called fugu), Takifugu rubripes, it appears to be rejected by a close congener, grass pufferfish, Takifugu niphobles, after initial attachment to the gills. To determine the genetic architecture of the pufferfish responsible for this host specificity, we performed genome-wide quantitative trait loci analysis. We raised second generation (F₂) hybrids of the two pufferfish species and experimentally infected them with the monogenean in vivo. To assess possible differences in host mechanisms between early and later periods of infection, we sampled fish three h and 21 days after exposure. Genome scanning of fish from the 3 h infection trial revealed suggestive quantitative trait loci on linkage groups 2 and 14, which affected the number of parasites on the gill. However, analysis of fish 21 days p.i. detected a significant quantitative trait locus on linkage group 9 and three other suggestive quantitative trait loci on linkage groups 7, 18 and 22. These results indicated the polygenic nature of the host mechanisms involved in the infection/rejection of H. okamotoi. Moreover the analyses suggested that host factors may play a more important role during the growth period of the parasite than during initial host recognition at the time of attachment. Within the 95% confidence interval of the linkage group 9 quantitative trait locus in the fugu genome, there were 214 annotated protein-coding genes, including immunity-related genes such as Irak4, Muc2 and Muc5ac.     

Production of Strigolactones by Arabidopsis thaliana responsible for Orobanche aegyptiaca seed germination

The germination stimulants produced by Arabidopsis thaliana, a host of root parasitic plants Orobanche spp. but not of arbuscular mycorrhizal (AM) fungi were examined. Root exudates from the hydroponically grown A. thaliana plants were subjected to reverse phase high performance liquid chromatography (HPLC) and retention times of germination stimulants inducing O. aegyptiaca seed germination were compared with those of strigolactone standards. In addition, the root exudates were analyzed by using HPLC linked with tandem mass spectrometry (LC/MS/MS). A. thaliana was found to exude at least three different germination stimulants of which one was identified as orobanchol. This is the first report of strigolactone production by a non-mycotrophic plant. These results together with recent knowledge imply that strigolactones have other unrevealed functions in plant growth and development.     

Vegetative/Parasitic transition: control and plasticity in striga development

Striga asiatica (Scrophulariaceae), an obligate parasite of grasses including many of the world's major grain crops, switches from vegetative to parasitic development by the differentiation of the root meristem into the host attachment organ, the haustorium. This change was induced in culture by the exposure to a single, low molecular weight signal molecule, 2,6-dimethoxy-p-benzo-quinone. A concentration of 10⁻⁶ molar quinone and an exposure time of ≥6 hours were required before the developmental process could be completed. With shorter exposure times, haustorial development was prematurely aborted and meristematic elongation was reestablished. The new meristem was capable of developing a second haustorium if reexposed to the signal molecule. These results are discussed in terms of the transition to the parasitic phase and the general control of plant cellular development.     

Arabidopsis thaliana model system reveals a continuum of responses to root endophyte colonization

We surveyed the non-mycorrhizal model plant Arabidopsis thaliana microscopically for its ability to form dark septate endophyte (DSE) symbioses in field, greenhouse, and laboratory studies. The laboratory studies were also used to estimate host growth responses to 34 Periconia macrospinosa and four Microdochium sp. isolates. Consistent with broad host range observed in previous experiments, field-, greenhouse-, and laboratory-grown A. thaliana were colonized by melanized inter- and intracellular hyphae and microsclerotia or chlamydospores indicative of DSE symbiosis. Host responses to colonization were variable and depended on the host ecotype. On average, two A. thaliana accessions (Col-0 and Cvi-0) responded negatively, whereas one (Kin-1) was unresponsive, a conclusion consistent with our previous analyses with forbs native to the field site where the fungi originate. Despite the average negative responses, examples of positive responses were also observed, a conclusion also congruent with earlier studies. Our results suggest that A. thaliana has potential as a model for more detailed dissection of the DSE symbiosis. Furthermore, our data suggest that host responses are controlled by variability in the host and endophyte genotypes.     

Endogenous gibberellins in clover broomrape,a parasitic plant,and its host,clover: Dependency of the parasite on the host for gibberellin production

Endogenous gibberellins were analyzed from a parasitic plant, clover broomrape (Orobanche minor Smith), and its host, clover (Trifolium repens L.). Members of both the early-13- and the early-non-hydroxylation pathways were identified from both the parasite and the host (GA₁₂, GA₂₄, GA₉ GA₄, GA₄₄, GA₁₉, GA₂₀, and GA₁ from clover broomrape; GA₉, GA₄, GA₄₄, GA₁₉, GA₂₀, and GA₁ from clover). Quantitative analyses showed that GA₄₄ was present at high levels in both host and parasite. The similarity in the gibberellins suggests the possibility that the major gibberellins in clover broomrape are transported from clover. However gibberellins such as GA₅₈, GA₃₈, and notably GA₄₇ which was identified from a plant for the first time were detected only from clover broomrape, suggesting that the parasite may have the ability to produce at least those gibberellins