Impacts of parasitic plants on natural communities

Chromosome-level genome assembly of Pedicularis kansuensis illuminates genome evolution of facultative parasitic plant

Parasitic plants have a heterotrophic lifestyle, in which they withdraw all or part of their nutrients from their host through the haustorium. Despite the release of many draft genomes of parasitic plants, the genome evolution related to the parasitism feature of facultative parasites remains largely unknown. In this study, we present a high-quality chromosomal-level genome assembly for the facultative parasite Pedicularis kansuensis (Orobanchaceae), which invades both legume and grass host species in degraded grasslands on the Qinghai-Tibet Plateau. This species has the largest genome size compared with other parasitic species, and expansions of long terminal repeat retrotransposons accounting for 62.37% of the assembly greatly contributed to the genome size expansion of this species. A total of 42,782 genes were annotated, and the patterns of gene loss in P. kansuensis differed from other parasitic species. We also found many mobile mRNAs between P. kansuensis and one of its host species, but these mobile mRNAs could not compensate for the functional losses of missing genes in P. kansuensis. In addition, we identified nine horizontal gene transfer (HGT) events from rosids and monocots, as well as one single-gene duplication events from HGT genes, which differ distinctly from that of other parasitic species. Furthermore, we found evidence for HGT through transferring genomic fragments from phylogenetically remote host species. Taken together, these findings provide genomic insights into the evolution of facultative parasites and broaden our understanding of the diversified genome evolution in parasitic plants and the molecular mechanisms of plant parasitism.

Hemiparasite Phtheirospermum japonicum growth benefits from a second host and inflicts greater host damage with exogenous N supply

While parasites are likely to connect to multiple host plants in nature, parasitism dynamics under multiple association conditions remain unclear and are difficult to separate from competitive effects. In this study, a five-compartment split root-box was constructed to allow a single facultative root hemiparasite, Phtheirospermum japonicum, to connect to zero, one or two Medicago sativa hosts while maintaining constant plant number and independently controlling nutrient supply. In the first experiment, we found that P. japonicum derived equal, additive benefits from attachment to a second host irrespective of parasite N status. In the second experiment, parasites were grown at four N levels in either parasitic or control conditions. Attachment caused a constant, absolute increase in parasite mass at all N levels, while host damage increased at higher parasite N levels despite an apparent decrease in host to parasite N transfer. Our findings suggest that host damage caused by P. japonicum may be strengthened by exogenous nitrogen supply to the parasite.

Effects of litter amount and seed sowing position on seedling emergence and growth of hemiparasitic Rhinanthus species under drought stress

Roadside vegetation in Central Europe is mostly species-poor and dominated by a few grass species. Hemiparasitic plant species, including Rhinanthus spp., might effectively restrict grass growth, thereby making space for light-dependent herb species. Despite the significance of abiotic site conditions for plant establishment in general, their effects on Rhinanthus establishment are less well known. We investigated combined effects of water availability, litter amount and seed position within litter on Rhinanthus seedling emergence and growth. Two parallel greenhouse experiments were conducted with R. angustifolius and R. minor. In these, we tested the impact of 200 or 400 g litter·m-2 with seeds sown beneath or on top of a litter layer under constantly humid or intermittently dry conditions on seedling emergence and biomass production of Rhinanthus. Presence of litter positively affected Rhinanthus seedling emergence when sown beneath the litter layer and reduced negative effects of water deficiency. Sowing beneath a litter layer increased seedling emergence by 157%, with similar effects at 200 and 400 g litter·m-2. Water level did not affect biomass production. Compared to R. minor, R. angustifolius had higher mean biomass, and its seedlings emerged earlier and in higher numbers. Our results indicate that Rhinanthus spp. react similarly to litter as non-hemiparasitic plant species from temperate grasslands. Litter presence positively influenced Rhinanthus seedling emergence and growth under intermittently dry conditions. Its hemiparasitic characteristics might reduce drought impacts on biomass production. To ensure seed contact with the soil surface, seeds should be sown when no litter is present, or mulching should occur post-sowing.

Rising from the shadows: Selective foraging in model shoot parasitic plants

Despite being sessile, plants nonetheless forage for resources by modulating their growth. Adaptative foraging in response to changes in resource availability and presence of neighbours has strong implications for performance and fitness. It is an even more pressing issue for parasitic plants, which draw resources directly from other plants. Indeed, parasitic plants were demonstrated over the years to direct their growth towards preferred hosts and invest resources in parasitism relative to host quality. In contrast to root parasites that rely mostly on chemical cues, some shoot parasites seem to profit from the ability to integrate different types of abiotic and biotic cues. While significant progress in this field has been made recently, there are still many open questions regarding the molecular perception and the integration of diverse signalling pathways under different ecological contexts. Addressing how different cues are integrated in parasitic plants will be important when unravelling variations in plant interaction pathways, and essential to predict the spread of parasites in natural and agricultural environments. In this review, we discuss this with a focus on Cuscuta species as an emerging parasitic model, and provide research perspectives based on the recent advances in the topic and plant-plant interactions in general.

Photosynthesis, ionomics and metabolomics of the host-hemiparasite association Acacia gerrardii-Viscum schimperi

Viscum schimperi is an evergreen hemiparasitic plant that can grow on stems and branches of several tree species. It penetrates the host tissues and forms a vascular bridge (haustorium) to withdraw the nutritive resources. Its relationships with hosts remain unknown. This study aimed to investigate the physiological and biochemical attributes of the host-hemiparasite association Acacia gerrardii -Viscum schimperi . The hemiparasite exhibited 2.4- and 3.0-fold lower photosynthetic activity and water use efficiency, and 1.2- and 4.1-fold higher transpiration rate and stomatal conductance. Equally, it displayed 4.9- and 2.6-fold greater water potential and osmotic potential, and in least 3.0times more accumulated 39 K, 85 Rb and 51 V, compared to the host. Nevertheless, it had no detrimental effect on photosynthetic activity, water status and multi-element accumulations in the host. Based on metabolome profiling, V. schimperi could use xanthurenic acid and propylparaben to acquire potassium from the host, and N -1-naphthylacetamide and N -Boc-hydroxylamine to weaken or kill the distal part of the infected branch and to receive the total xylem contents. In contrast, A. gerrardii could used N -acetylserotonin, arecoline, acetophenone and 6-methoxymellein to defend against V. schimperi infection.

What explains the high island endemicity of Philippine Rafflesia? A species distribution modeling analysis of three threatened parasitic plant species and their hosts

PREMISE

Rafflesia are rare holoparasitic plants. In the Philippines, all but one species are found only on single islands. This study aimed to better understand the factors contributing to this distributional pattern. Specifically, we sought to determine whether narrow environmental tolerances of host and/or parasite species might explain their island endemicity.

METHODS

We used Maxent species distribution modeling to identify areas with suitable habitat for R. lagascae, R. lobata, and R. speciosa and their Tetrastigma host species. These analyses were carried out for current climate conditions and two future climate change scenarios.

RESULTS

Although species distribution models indicated suitable environmental conditions for the Tetrastigma host species in many parts of the Philippines, considerably fewer areas were inferred to have suitable conditions for the three Rafflesia species. Some of these areas are on islands from which they have not been reported. All three species will face significant threats as a result of climate change.

CONCLUSIONS

Our results suggest that limited inter-island dispersibility and/or specific environmental requirements are likely responsible for the current pattern of island endemicity of the three Rafflesia species, rather than environmental requirements of their Tetrastigma host species.

Effect of Parasitic Native Plant Cuscuta australis on Growth and Competitive Ability of Two Invasive Xanthium Plants

The competitive ability of invasive plants is a key factor in their successful invasion, and research on this ability of invasive plants can provide a theoretical basis for the prevention and control of invasive plants. This study used Cuscuta australis, Xanthium spinosum, and Xanthium italicum as research materials and conducted outdoor controlled pot experiments to compare and study the changes in the biomass, competitiveness, and growth cycle of X. spinosum and X. italicum parasitized by C. australis at different growth stages. The results showed that (1) parasitism by C. australis increased the biomass of X. spinosum and decreased that of X. italicum, but under parasitism, the root cap ratio of X. spinosum and X. italicum increased, and the fruit biomass ratio decreased, indicating that X. spinosum and X. italicum reduced the energy input for reproduction and increased the energy input for nutrient growth to resist the impact of C. australis parasitism; (2) the relative competitive intensity calculated based on the total biomass of a single plant showed a negative value for X. spinosum during parasitism at the flowering and fruit stages, indicating an increase in competitive ability, and X. italicum showed a positive value during parasitism at the seedling and flowering stages, indicating a decrease in competitive ability; and (3) the parasitism of C. australis significantly shortened the fruit stage of X. spinosum and X. italicum, leading to a significant advance in their flowering, fruiting, and fruit ripening times. Simultaneously, it significantly reduced the morphological indicators of biomass, plant height, and crown width. Thus, C. australis parasitism has a certain inhibitory effect on the competitive ability of some invasive plants and can shorten their growth cycle, the latter of which has an important impact on their reproduction and diffusion.

Invited Review Beyond parasitic convergence: unravelling the evolution of the organellar genomes in holoparasites

BACKGROUND

The molecular evolution of organellar genomes in angiosperms has been studied extensively, with some lineages, such as parasitic ones, displaying unique characteristics. Parasitism has emerged 12 times independently in angiosperm evolution. Holoparasitism is the most severe form of parasitism, and is found in ~10 % of parasitic angiosperms. Although a few holoparasitic species have been examined at the molecular level, most reports involve plastomes instead of mitogenomes. Parasitic plants establish vascular connections with their hosts through haustoria to obtain water and nutrients, which facilitates the exchange of genetic information, making them more susceptible to horizontal gene transfer (HGT). HGT is more prevalent in the mitochondria than in the chloroplast or nuclear compartments.

SCOPE

This review summarizes current knowledge on the plastid and mitochondrial genomes of holoparasitic angiosperms, compares the genomic features across the different lineages, and discusses their convergent evolutionary trajectories and distinctive features. We focused on Balanophoraceae (Santalales), which exhibits extraordinary traits in both their organelles.

CONCLUSIONS

Apart from morphological similarities, plastid genomes of holoparasitic plants also display other convergent features, such as rampant gene loss, biased nucleotide composition and accelerated evolutionary rates. In addition, the plastomes of Balanophoraceae have extremely low GC and gene content, and two unexpected changes in the genetic code. Limited data on the mitochondrial genomes of holoparasitic plants preclude thorough comparisons. Nonetheless, no obvious genomic features distinguish them from the mitochondria of free-living angiosperms, except for a higher incidence of HGT. HGT appears to be predominant in holoparasitic angiosperms with a long-lasting endophytic stage. Among the Balanophoraceae, mitochondrial genomes exhibit disparate evolutionary paths with notable levels of heteroplasmy in Rhopalocnemis and unprecedented levels of HGT in Lophophytum. Despite their differences, these Balanophoraceae share a multichromosomal mitogenome, a feature also found in a few free-living angiosperms.

Parasitic plant-host interaction between the holoparasite Cytinus hypocistis and the shrub Cistus albidus in their natural Mediterranean habitat: local and systemic hormonal effects

Mediterranean-type ecosystems provide a unique opportunity to study parasitic plant-host interactions, such as the relationship between the dominant shrub Cistus albidus L. and the root holoparasitic plant Cytinus hypocistis L. We examined this interaction (i) locally, by measuring the hormonal profiling of the interaction zone between the holoparasitic plant and the host, and (ii) systemically, by examining the hormonal profiling and physiological status of leaves from infested and uninfested plants. Furthermore, we explored how temporal variation (seasonal effects) and geographical location influenced the systemic hormonal and physiological response of leaves. Results shed light on tissue-related variations in hormones, suggesting the parasite exerted a sink effect, mainly influenced by cytokinins. Jasmonates triggered a defense response in leaves, far from the infestation point, and both jasmonates and abscisic acid (ABA) appeared to be involved in the tolerance to holoparasitism when plants were simultaneously challenged with summer drought. Parasitism did not have any major negative impact on the host, as indicated by physiological stress markers in leaves, thus indicating a high tolerance of the shrub C. albidus to the root holoparasitic plant C. hypocistis. Rather, parasitism seemed to exert a priming-like effect and some compensatory effects were observed (increased chlorophyll contents) in the host under mild climatic conditions. We conclude that (i) cytokinins, jasmonates and ABA play a role at the local and systemic levels in the response of C. albidus to the biotic stress caused by C. hypocistis, and that (ii) seasonal changes in environmental conditions and geographical location may impact holoparasitic plant-host interactions in the field, modulating the physiological response.

Parasite-host network analysis provides insights into the evolution of two mistletoe lineages (Loranthaceae and Santalaceae)

Mistletoes are ecologically important parasitic plants, with > 1600 species from five lineages worldwide. Mistletoe lineages exhibit distinct patterns of species diversification and host specificity, however, the mechanisms underlying these differences are poorly understood. In this study, we analysed a comprehensive parasite-host network, including 280 host species from 60 families and 22 mistletoe species from two lineages (Santalaceae and Loranthaceae) in Xishuangbanna, located in a biodiversity hotspot of tropical Asia. We identified the factors that predict the infection strength of mistletoes. We also detected host specificity and the phylogenetic signal of mistletoes and their hosts. We found that this interaction network could be largely explained by a model based on the relative abundance of species. Host infection was positively correlated with diameter at breast height and tree coverage, but negatively correlated with wood density. Overall, closely related mistletoe species tend to interact more often with similar hosts. However, the two lineages showed a significantly different network pattern. Rates of host generality were higher in Loranthaceae than in Santalaceae, although neither lineage showed phylogenetic signal for host generality. This study demonstrates that the neutral interaction hypothesis provides suitable predictions of the mistletoe-host interaction network, and mistletoe species show significant phylogenetic signals for their hosts. Our findings also indicate that high species diversification in Loranthaceae may be explained by high rates of host generality and the evolutionary history shared by Loranthaceae species with diverse host plants in the tropics.

Stigmas of holoparasitic Phelipanche arenaria (Orobanchaceae) - a suitable ephemeric flower habitat for development unique microbiome

BACKGROUND

Microbial communities have occasionally been observed in part of the ephemeric reproductive structure of floral stigmas, but their prevalence, phylogenetic diversity and ecological roles are understudied. This report describes the first study of bacterial and fungal communities in immature and mature stigma tissue of the endangered holoparasitic plant Phelipanche arenaria. Culture-dependent methods coupled with next-generation sequencing indicated that a small surface of the flower stigma was an unexpectedly rich and diverse microhabitat for colonization of microbial. We also compared the enzymatic activity of the bacterial communities between immature and mature stigmas samples.

RESULTS

Using high-throughput sequencing methods, we identified and classified 39 to over 51 OTUs per sample for bacterial OTUs represented by Pantoea agglomerans and P. ananatis, comprising 50.6%, followed by Pseudomonas, Luteibacter spp., Sphingomonas spp. with 17% of total frequency. The bacterial profile of immature stigmas of P. arenaria contained unique microorganisms (21 of the most numerous OTUs) that were not confirmed in mature stigmas. However, the enzymatic activity of bacteria in mature stigmas of P. arenaria showed more activity than observed in immature stigmas. In the fungal profile, we recorded even 80 OTUs in mature stigmas, consisting of Capnodiales 45.03% of the total abundance with 28.27% of frequency was created by Alternaria eichhorniae (10.55%), Mycosphaerella tassiana (9.69%), and Aureobasidium pullulans (8.03%). Additionally, numerous putative plant growth-promoting bacteria, fungal pathogens and pathogen-antagonistic yeasts were also detected.

CONCLUSIONS

Our study uncovered that P. arenaria stigmas host diverse bacterial and fungal communities. These microorganisms are well known and have been described as beneficial for biotechnological and environmental applications (e.g., production of different enzymes and antimicrobial compounds). This research provided valuable insight into the parasitic plant-microbe interactions.

Effect of global warming on the potential distribution of a holoparasitic plant (Phelypaea tournefortii): both climate and host distribution matter

Phelypaea tournefortii (Orobanchaceae) primarily occurs in the Caucasus (Armenia, Azerbaijan, Georgia, and N Iran) and Turkey. This perennial, holoparasitic herb is achlorophyllous and possesses one of the most intense red flowers among all plants worldwide. It occurs as a parasite on the roots of several Tanacetum (Asteraceae) species and prefers steppe and semi-arid habitats. Climate change may affect holoparasites both directly through effects on their physiology and indirectly as a consequence of its effects on their host plants and habitats. In this study, we used the ecological niche modeling approach to estimate the possible effects of climate change on P. tournefortii and to evaluate the effect of its parasitic relationships with two preferred host species on the chances of survival of this species under global warming. We used four climate change scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5) and three different simulations (CNRM, GISS-E2, INM). We modeled the species' current and future distribution using the maximum entropy method implemented in MaxEnt using seven bioclimatic variables and species occurrence records (Phelypaea tournefortii - 63 records, Tanacetum argyrophyllum - 40, Tanacetum chiliophyllum - 21). According to our analyses, P. tournefortii will likely contract its geographical range remarkably. In response to global warming, the coverage of the species' suitable niches will decrease by at least 34%, especially in central and southern Armenia, Nakhchivan in Azerbaijan, northern Iran, and NE Turkey. In the worst-case scenario, the species will go completely extinct. Additionally, the studied plant's hosts will lose at least 36% of currently suitable niches boosting the range contraction of P. tournefortii. The GISS-E2 scenario will be least damaging, while the CNRM will be most damaging to climate change for studied species. Our study shows the importance of including ecological data in niche models to obtain more reliable predictions of the future distribution of parasitic plants.

Mealybugs (Hemiptera, Coccomorpha, Pseudococcidae) on parasitic plants (Loranthaceae) in Indonesia with description of a new species and a new country record

Parasitic plants have been known to be attacked by insect pests since ancient times. However, little is known about the mealybug (Hemiptera, Coccomorpha, Pseudococcidae) fauna associated with them. A series of surveys of mealybugs found on Loranthaceae, a semi-parasitic plant family, was conducted in several places in Bengkulu Province, southern Sumatra, Indonesia. In the study, 55 mealybug specimens were collected, consisting of eight species belonging to five genera, namely Chorizococcus McKenzie (1 species), Dysmicoccus Ferris (2 species), Ferrisia Fullaway (1 species), Planococcus Ferris (3 species) and Pseudococcus Westwood (1 species). Chorizococcusozeri Zarkani & Kaydan, sp. nov. is new to science, whilst Planococcusbagmaticus Williams represents the first record in Indonesia. In addition, the mealybugs Dysmicoccuslepelleyi (Betrem), Dysmicoccuszeynepae Zarkani & Kaydan, Ferrisiadasylirii (Cockerell), Planococcuslilacinus (Cockerell) and Pseudococcusjackbeardsleyi Gimpel & Miller are newly recorded from plants of the family Loranthaceae. Figures and illustrations of mealybug species with a taxonomic key to Asian Chorizococcus and a new country record based on morphological characters are also updated.

Resource availability and parasitism intensity influence the response of soybean to the parasitic plant Cuscuta australis

Introduction

Parasitic plants can damage crop plants and consequently cause yield losses and thus threaten food security. Resource availability (e.g., phosphorus, water) has an important role in the response of crop plants to biotic attacks. However, how the growth of crop plants under parasitism are affected by environmental resource fluctuation is poorly understood.

Methods

We conducted a pot experiment to test the effects of the intensity of Cuscuta australis parasitism and the availability of water and phosphorus (P) on soybean shoot and root biomass.

Results and discussion

We found that low-intensity parasitism caused ~6% biomass reduction, while high-intensity parasitism caused ~26% biomass reduction in soybean. Under 5-15% water holding capacity (WHC), the deleterious effect of parasitism on soybean hosts was ~60% and ~115% higher than that under 45-55% WHC and 85-95% WHC, respectively. When the P supply was 0 μM, the deleterious effect of parasitism on soybean was 67% lower than that when the P supply was 20 μM. Besides, the biomass of C. australis was highest when both the water and the P availability were lowest. Cuscuta australis caused the highest damage to soybean hosts under 5 μM P supply, 5-15% WHC, and high-intensity parasitism. Additionally, C. australis biomass was significantly and negatively related to the deleterious effect of parasitism on soybean hosts and to the total biomass of soybean hosts under high-intensity parasitism, but not under low-intensity parasitism. Although high resource availability can promote soybean growth, the two resources have different impacts on the response of hosts to parasitism. Higher P availability decreased host tolerance to parasites, while higher water availability increased host tolerance. These results indicate that crop management, specifically water and phosphorus supply, can efficiently control C. australis in soybean. To our best knowledge, this appears to be the first study to test the interactive effect of different resources on the growth and response of host plants under parasitism.

Diverse Host Spectrum and the Parasitic Process in the Pantropical Hemiparasite Cassytha filiformis L. (Lauraceae) in China

Many hemiparasites attach to a range of different host species, resulting in complex parasite–host interactions. Comprehensive molecular phylogenies allow the investigation of evolutionary relationships between these host plants. We surveyed the hosts of the laurel dodder (Cassytha filiformis, Lauraceae) in China, representing 184 species from 146 genera, 67 families, and spanning flowering plants, conifers, and ferns, using host phylogenetic relationships to investigate the susceptibility to attack by this hemiparasitic plant among the vascular plants. The process of produced well-formed haustoria by C. filiformis was also observed in detail for six different hosts. Our results show that C. filiformis grows mainly on trees and shrubs from phylogenetically divergent members of the rosid and asterid eudicot clades, often attacking multiple adjacent hosts simultaneously, and forming extensive colonies. However, whether and to what extent transitions between C. filiformis and host plants occur remain unclear. Physiological evidence for the complex parasite–host species interactions need to be studied in the future.

Host Resistance to Parasitic Plants-Current Knowledge and Future Perspectives

Parasitic flowering plants represent a diverse group of angiosperms, ranging from exotic species with limited distribution to prominent weeds, causing significant yield losses in agricultural crops. The major damage caused by them is related to the extraction of water and nutrients from the host, thus decreasing vegetative growth, flowering, and seed production. Members of the root parasites of the Orobanchaceae family and stem parasites of the genus Cuscuta are among the most aggressive and damaging weeds, affecting both monocotyledonous and dicotyledonous crops worldwide. Their control and eradication are hampered by the extreme seed longevity and persistence in soil, as well as their taxonomic position, which makes it difficult to apply selective herbicides not damaging to the hosts. The selection of resistant cultivars is among the most promising approaches to deal with this matter, although still not widely employed due to limited knowledge of the molecular mechanisms of host resistance and inheritance. The current review aims to summarize the available information on host resistance with a focus on agriculturally important parasitic plants and to outline the future perspectives of resistant crop cultivar selection to battle the global threat of parasitic plants.

Transcriptome analysis reveals defense-related genes and pathways during dodder (Cuscuta australis) parasitism on white clover (Trifolium repens)

Dodders (Cuscuta australis R. Br.) are holo-parasitic stem angiosperms with an extensive host range that have significant ecological and economic potential impact on the ecosystem and the agricultural system. However, how the host plant responds to this biotic stress remains mostly unexplored. To identify the defense-related genes and the pathways in white clover (Trifolium repens L.) induced by dodder parasitism, we performed a comparative transcriptome analysis of the leaf and root tissues from white clover with and without dodder infection by high throughput sequencing. We identified 1,329 and 3,271 differentially expressed genes (DEGs) in the leaf and root tissues, respectively. Functional enrichment analysis revealed that plant-pathogen interaction, plant hormone signal transduction, and phenylpropanoid biosynthesis pathways were significantly enriched. Eight WRKY, six AP2/ERF, four bHLH, three bZIP, three MYB, and three NAC transcription factors showed a close relationship with lignin synthesis-related genes, which defended white clover against dodder parasitism. Real-time quantitative PCR (RT-qPCR) for nine DEGs, further validated the data obtained from transcriptome sequencing. Our results provide new insights into understanding the complex regulatory network behind these parasite-host plant interactions.

A comparative study across the parasitic plants of Cuscuta subgenus Grammica (Convolvulaceae) reveals a possible loss of the plastid genome in its section Subulatae

Most species in Cuscuta subgenus Grammica retain many photosynthesis-related plastid genes, generally under purifying selection. A group of holoparasitic species in section Subulatae may have lost their plastid genomes entirely. The c. 153 species of plants belonging to Cuscuta subgenus Grammica are all obligate stem parasites. However, some have completely lost the ability to conduct photosynthesis while others retain photosynthetic machinery and genes. The plastid genome that primarily encodes key photosynthesis genes functions as a bellwether for how reliant plants are on primary production. This research assembles and analyses 17 plastomes across Cuscuta subgenus Grammica with the aim of characterizing the state of the plastome in each of its sections. By comparing the structure and content of plastid genomes across the subgenus, as well as by quantifying the selection acting upon each gene, we reconstructed the patterns of plastome change within the phylogenetic context for this group. We found that species in 13 of the 15 sections that comprise Grammica retain the bulk of plastid photosynthesis genes and are thus hemiparasitic. The complete loss of photosynthesis can be traced to two clades: the entire section Subulatae and a complex of three species within section Ceratophorae. We were unable to recover any significant plastome sequences from section Subulatae, suggesting that plastomes in these species are either drastically reduced or lost entirely.

Host root exudates initiate a foraging preference by the root parasite Santalum album

Haustoria of root-parasitic plants draw nutrients from the roots of host species. While recent studies have assessed host preferences of parasitic plants, how root-exuded chemicals can mediate host tropism and selection by root-parasitic plants is poorly understood. Under greenhouse conditions, we performed two pot experiments to determine whether the root parasite Santalum album selectively forages for superior hosts (N2-fixing Acacia confusa Merr. or Dalbergia odorifera T. Chen) rather than for inferior hosts (non-N2-fixing Bischofia polycarpa (levl.) Airy Shaw or Dracontomelon duperreranum Pierre), and whether S. album uses host root exudates and/or specific chemicals in these root exudates to locate and trigger haustorium formation. Lateral roots and haustoria of S. album seedlings exhibited greater growth in the direction of D. odorifera roots than toward roots from the other three hosts. Comparative metabolic analysis revealed that D. odorifera root exudates were enriched in isoflavonoid, flavonoid and flavone/flavonol biosynthesis pathways, and that the relative contents of flavonoids were significantly greater in the root exudates of D. odorifera than in those of the other three hosts. Root exudates from D. odorifera significantly promoted S. album root growth, haustorium formation and reactive oxygen species accumulation in haustoria. Our results demonstrate that the key step in plant parasitism by S. album is based on root exudation by a host plant; the exudates function as a metabolite signal that activate lateral root growth and haustorium formation. Our results also indicate that flavonoids in the root exudates could play an important role in S. album foraging activity. Information on the responses of root parasites to host root exudates and/or haustorium-inducing chemicals may be useful for selecting superior host species to plant with valuable species of root parasites.

Performance of a parasitic plant and its effects on hosts depends on the interactions between parasite seed family and host species

Root hemiparasitic plants act as keystone species influencing plant community composition through their differential suppression of host species. Their own performance also strongly depends on interactions with host species. However, little is known about the roles of parasite genetic variation vs. plasticity in these interactions. We grew plants from eight maternal families of the root hemiparasite Rhinanthus alectorolophus with six potential host species (two grasses, two legumes and two forbs) and without a host and measured fitness-related and morphological traits of the parasite, host biomass and overall productivity. Parasite biomass and other traits showed strong plastic variation in response to different host species, but were also affected by parasite maternal family. Parasite seed families responded differently to the hosts, indicating genetic variation that could serve as the basis for adaptation to different host plants. However, there were no negative correlations in the performance of families across different hosts, indicating that R. alectorolophus has plastic generalist genotypes and is not constrained in its use of different host species by trade-offs in performance. Parasite effects on host biomass (which may indicate virulence) and total productivity (host + parasite biomass) depended on the specific combination of parasite family and host species. Mean biomass of hosts with a parasite family and mean biomass of that family tended to be negatively correlated, suggesting selection for maximum resource extraction from the hosts. Specialization of generalist root hemiparasites may be restricted by a lack of trade-offs in performance across hosts, together with strong spatial and temporal variation in host species availability. The genetic variation in the effects on different hosts highlights the importance of genetic diversity of hemiparasites for their effects on plant community structure and productivity and for the success of using them to restore grassland diversity.

Parasitism Shifts the Effects of Native Soil Microbes on the Growth of the Invasive Plant Alternanthera philoxeroides

Soil microbes play an important role in plant invasion, and parasitic plants regulate the growth of invasive plants. However, the mechanisms by which parasitic plants regulate the effects of soil microbes on invasive plants have not been investigated. Here, we used the invasive plant Alternanthera philoxeroides and the holoparasitic plant Cuscuta grovonii to test whether and how C. grovonii parasitism shifts the effect of native soil microbes on the growth of A. philoxeroides. In a factorial setup, A. philoxeroides was grown in pots with the presence versus absence of parasitism and the presence versus absence of native soil microbes. The findings showed that native soil microbes increased the biomass and clonal growth of A. philoxeroides only in the absence of a parasite, whereas parasitism decreased the biomass and clonal growth of A. philoxeroides only in the presence of soil microbes. In addition, the presence of soil microbes increased the deleterious effects of the parasite on A. philoxeroides. These results indicate that parasitism can shift the effects of native soil microbes on the growth of the invasive plant A. philoxeroides. Our results enrich the understanding of the mechanisms underlying the success of plant invasion.

A new species of Struthanthus Mart. (Loranthaceae) from Oaxaca, Mexico

Struthanthusibe-dzisp. nov. is a new species described and illustrated from the cloud and pine-oak forests of the Sierra Madre del Sur in Oaxaca, Mexico. This species shares similarities of leaf shape and inflorescence type with S.deppeanus, S.quercicola, and S.ramiro-cruzii. However, S.ibe-dzi can be recognized by its glaucous branches, leaves and inflorescences; compressed nodes; convoluted distal half of styles in pistillate flowers; and staminate flowers with asymmetrical thecae and an extended connective forming an apiculate horn in both anther series. A distribution map and an identification key are provided to separate S.ibe-dzi from morphologically similar congeners present in the region.

Inflorescences of Cuscuta (Convolvulaceae): Diversity, evolution and relationships with breeding systems and fruit dehiscence modes

Cuscuta (dodder) includes ca. 200 species of plant obligate stem parasites with enormous ecological and economical significance. Inflorescences have been historically used in Cuscuta for species descriptions and identification keys, but no comprehensive study exists to date. The main objectives of this study were to survey the diversity and evolution of inflorescences and to uncover their possible form-function relationships. The inflorescence architecture of 132 Cuscuta taxa was analysed using herbarium specimens and eight species were grown to study their inflorescence development. Inflorescence traits were mapped into a genus phylogeny obtained from a combined analysis of nuclear ITS and plastid trnL-F sequences. To test the hypothesis that inflorescence architecture is connected to sexual reproduction, correlations between inflorescence traits (using Principal Components), sexual reproductive traits (pollen/ovule ratios, corolla length and diameter), fruit charaters (fruit length and width), and the modes of dehiscence were analyzed. Based on their development, three major types of inflorescences were observed: "Cuscuta type", a simple, monochasial scorpioid cyme; "Monogynella type", a compound monochasial scorpioid cymes with the longest primary axes having prolonged vegetative growth and giving the appearance of thyrses; and "Grammica type", a compound monochasial scorpiod cymes with up to five orders of axes. Maximum likelihood analyses suggested Monogynella as the ancestral type, while Cuscuta and Grammica were derived. Overall, the total length of axes exhibited a reduction trend throughout the genus evolution, but it was not correlated with the pedicels length. Inflorescences with similar architectures may exhibit contrasting pollen-ovule ratios. Positive significant correlations were noted between the size of the flower traits and pollen-ovule ratios. Several modes of dehiscence had statistically significant different total axes lengths, suggesting that the infructescence architecture is connected to the modes of dehiscence in Cuscuta and therefore seed dispersal.

Some characteristics of woody plants inhabited by Viscum album (Santalaceae) in the city of Kyiv

As a result of the study, a wide range of tree species parasitized by white mistletoe (Vіscum album) in the city of Kyiv, Ukraine, was identified. Some species, such as Quercus robur, Ulmus pumila, and Alnus glutinosa, remained uninfested even in the case of a high degree of infestation of surrounding trees. It has been found that among the infested plants only 4.34% of deciduous species and 5.05% of conifers demonstrated a severe damage caused by the hemiparasite (more than 20 plants of V. album in one crown). The largest number of trees and the highest level of damage were observed for Acer saccharinum, A. platanoides, Salix alba, Robinia pseudoacacia, Populus nigra, Tilia cordata, and Betula pendula aged in average 45–50 years. In the study of genetic characteristics of affected and unaffected by V. album trees of Pinus sylvestris at the molecular level by TBP markers, no differences have been revealed.

Metabolic changes induced by Cuscuta campestris Yunck in the host species Artemisia campestris subsp. variabilis (Ten.) Greuter as a strategy for successful parasitisation

C. campestris parasitisation increases internal host defences at the expense of environmentally directed ones in the host species A. campestris, thus limiting plant defence against progressive parasitisation. Cuscuta campestris Yunck is a holoparasitic species that parasitises wild species and crops. Among their hosts, Artemisia campestris subsp. variabilis (Ten.) Greuter is significantly affected in natural ecosystems. Limited information is available on the host recognition mechanism and there are no data on the interactions between these species and the effects on the primary and specialised metabolism in response to parasitisation. The research aims at evaluating the effect of host-parasite interactions, through a GC-MS untargeted metabolomic analysis, chlorophyll a fluorescence, ionomic and δ¹³C measurements, as well as volatile organic compound (VOC) fingerprint in A. campestris leaves collected in natural environment. C. campestris parasitisation altered plant water status, forcing stomatal opening, stimulating plant transpiration, and inducing physical damages to the host antenna complex, thus reducing the efficiency of its photosynthetic machinery. Untargeted-metabolomics analysis highlighted that the parasitisation significantly perturbed the amino acids and sugar metabolism, inducing an increase in the production of osmoprotectants, which generally accumulate in plants as a protective strategy against oxidative stress. Notably, VOCs analysis highlighted a reduction in sesquiterpenoids and an increase in monoterpenoids levels; involved in plant defence and host recognition, respectively. Moreover, C. campestris induced in the host a reduction in 3-hexenyl-acetate, a metabolite with known repellent activity against Cuscuta spp. We offer evidences that C. campestris parasitisation increases internal host defences via primary metabolites at the expense of more effective defensive compounds (secondary metabolites), thus limiting A. campestris defence against progressive parasitisation.

Mitigating the Mistletoe Menace: Biotechnological and Smart Management Approaches

Mistletoes have been considered a keystone resource for biodiversity, as well as a remarkable source of medicinal attributes that attract pharmacologists. Due to their hemiparasitic nature, mistletoes leach water and nutrients, including primary and secondary metabolites, through the vascular systems of their plant hosts, primarily trees. As a result of intense mistletoe infection, the hosts suffer various growth and physiological detriments, which often lead to tree mortality. Because of their easy dispersal and widespread tropism, mistletoes have become serious pests for commercial fruit and timber plantations. A variety of physical and chemical treatment methods, along with silvicultural practices, have shaped conventional mistletoe management. Others, however, have either failed to circumvent the growing range and tropism of these parasitic plants or present significant environmental and public health risks. A biocontrol approach that could sidestep these issues has never achieved full proof of concept in real-field applications. Our review discusses the downsides of conventional mistletoe control techniques and explores the possibilities of biotechnological approaches using biocontrol agents and transgenic technologies. It is possible that smart management options will pave the way for technologically advanced solutions to mitigate mistletoes that are yet to be exploited.

Why are some plant species missing from restorations? A diagnostic tool for temperate grassland ecosystems

The U.N. Decade on Ecosystem Restoration aims to accelerate actions to prevent, halt, and reverse the degradation of ecosystems, and re-establish ecosystem functioning and species diversity. The practice of ecological restoration has made great progress in recent decades, as has recognition of the importance of species diversity to maintaining the long-term stability and functioning of restored ecosystems. Restorations may also focus on specific species to fulfill needed functions, such as supporting dependent wildlife or mitigating extinction risk. Yet even in the most carefully planned and managed restoration, target species may fail to germinate, establish, or persist. To support the successful reintroduction of ecologically and culturally important plant species with an emphasis on temperate grasslands, we developed a tool to diagnose common causes of missing species, focusing on four major categories of filters, or factors: genetic, biotic, abiotic, and planning & land management. Through a review of the scientific literature, we propose a series of diagnostic tests to identify potential causes of failure to restore target species, and treatments that could improve future outcomes. This practical diagnostic tool is meant to strengthen collaboration between restoration practitioners and researchers on diagnosing and treating causes of missing species in order to effectively restore them.

Tapinanthus species: A review of botany and biology, secondary metabolites, ethnomedical uses, current pharmacology and toxicology

ETHNOPHARMACOLOGICAL RELEVANCE

Tapinanthus species are hemiparasites that grow on diverse hosts in African regions. Tapinanthus species are locally known as "all purpose herbs" as they are traditionally used to treat various diseases such as diabetes, hypertension, cancer, inflammation, malaria, anemia, anxiety, itching, and so on.

AIM OF THE STUDY

A comprehensive review on research outcomes and future perspectives of Tapinanthus species are presented to provide a reference for relevant researchers.

MATERIALS AND METHODS

The references regarding Tapinanthus species were retrieved from Google Scholar, Web of Science, Sci-finder, PubMed, Elsevier, Wiley, China National Knowledge Infrastructure, Open Access Library, and SpringerLink between 1963 and 2022. Scientific plant names were provided by "The Plant List" (www.theplantlist.org) and "The world Flora Online" (www.worldfloraonline.org).

RESULTS

Even though Tapinanthus species are regarded as notorious pests that can undermine various hosts, they are, as omnipotent herbs in folklore, meaningful for the development of potential phytomedicine sources. Phytochemistry screening has revealed the presence of glycosides, triterpenoids, flavonoids, alkaloids, tannins, steroids, anthraquinones. Among them, the chemical structures of 40 compounds have been elucidated by phytochemical methods without alkaloids and anthraquinones. These secondary metabolites might be responsible for ethnomedical uses and bioactivities of Tapinanthus species. Current research has provided scientific evidence for traditional uses of Tapinanthus species, especially unraveling hypoglycemic, hepatoprotective, antioxidant, antibacterial, anti-anxiety, anti-depression, anti-inflammatory, and other pharmacological properties. Given the fact that ethnomedical uses served as a valuable reference for pharmacology, however, some records to treat arthritis, fever, itching, dysentery, stomach pain, and anemia, have not been confirmed in current research. Furthermore, the toxic effects of Tapinanthus species were susceptible to the dosages, with relative safety across a wide range.

CONCLUSIONS

To reasonably yield Tapinanthus species, artificial culture might be a promising method to develop in the future. The discrepancies between phytochemistry screening and structure elucidation, as well as between ethnomedical uses and current pharmacology, need to be further clarified. The identification of bioactive compounds in crude extracts and fractions, the illustration of the underlying mechanisms of pharmacology, along with the addition of cytotoxicity, genotoxicity, and clinical trials of toxic tests, should be carried out in depth. This review highlights that Tapinanthus species can be considered promising phytomedicine sources as long as we adhere to digging more deeply into their potential role.

Root hemiparasitic plants are associated with more even communities across North America

Root hemiparasitic plants both compete with and extract resources from host plants. By reducing the abundance of dominant plants and releasing subordinates from competitive exclusion, they can have an outsized impact on plant communities. Most research on the ecological role of hemiparasites is manipulative and focuses on a small number of hemiparasitic taxa. Here, we ask whether patterns in natural plant communities match the expectation that hemiparasites affect the structure of plant communities. Our data were collected on 129 national park units spanning the continental United States. The most common hemiparasite genera were Pedicularis, Castilleja, Krameria, and Comandra. We used null models and linear mixed models to determine whether hemiparasites were associated with changes in community richness and evenness. Hemiparasite presence did not affect community metrics. Hemiparasite abundance was positively associated with increasing evenness of herbaceous species, but not with species richness. The associations that we observed on a continental scale are consistent with evidence that the impacts of root hemiparasitic plants on evenness can be substantial and abundance dependent but that effects on richness are less pronounced. Hemiparasites mediate competitive exclusion in communities to facilitate species coexistence and merit consideration of inclusion in ecological theories of coexistence.

The Angiosperm Stem Hemiparasitic Genus Cassytha (Lauraceae) and Its Host Interactions: A Review

Cassytha, also known as laurel dodder or love vine, is a stem hemiparasite of the Lauraceae family. It has long been used for medicinal purposes in many countries and has increasingly influenced agricultural and natural ecosystems by its effects on a wide range of host species. Previous studies have focused on the taxonomy and evolutionary position of different Cassytha, with the pan-tropical species Cassytha filiformis being the most widely studied. However, Cassytha-host interactions have never been reviewed, which is an essential issue related to the understanding of mechanisms underlying plant hemiparasitic and the assessment of benefits and damage caused by aerial parasitic plants. This review explores the parasitic habits, worldwide distribution, and host range of Cassytha, and examines its impacts on the biology of host plants and the overall influence of environmental changes on Cassytha-host associations. We also comment on areas of future research directions that require to better understanding Cassytha-host interactions. It appeared that some traits, such as flowering phenology, facilitated Cassytha's widespread distribution and successful parasitism and that Cassytha preferred woody species rather than herbaceous species as a host, and preferred species from certain families as hosts, such as Fabaceae and Myrtaceae. Cassytha often decreased biomass and impacted the physiology of host species and global environmental changes seemed to intensify the negative impacts of Cassytha on their hosts. Cassytha was not only a noxious weed, but can also function as a biocontrol agent to mitigate alien plant invasion.

Distinguishing carbon gains from photosynthesis and heterotrophy in C3-hemiparasite-C3-host pairs

BACKGROUND AND AIMS

Previous carbon stable isotope (13C) analyses have shown for very few C3-hemiparasites utilizing C4- or CAM-hosts the use of two carbon sources, autotrophy and heterotrophy. This 13C approach, however, failed for the frequently occurring C3-C3 parasite-host pairs. Thus, we used hydrogen stable isotope (2H) natural abundances as a substitute for 13C within a C3-Orobanchaceae sequence graded by haustoria complexity and C3-Santalaceae.

METHODS

Parasitic plants and their real or potential host plants as references were collected in Central European lowland and alpine mountain meadows and forests. Parasitic plants included the xylem-feeding holoparasite Lathraea squamaria parasitizing on the same carbon nutrient source (xylem-transported organic carbon compounds) as potentially Pedicularis, Rhinanthus, Bartsia, Melampyrum and Euphrasia hemiparasites. Reference plants were used for an autotrophy-only isotope baseline. A multi-element stable isotope natural abundance approach was applied.

KEY RESULTS

Species-specific heterotrophic carbon gain ranging from 0 to 51 % was estimated by a 2H mixing-model. The sequence in heterotrophic carbon gain mostly met the morphological grading by haustoria complexity: Melampyrum- < Rhinanthus- < Pedicularis-type.

CONCLUSION

Due to higher transpiration and lower water-use efficiency, depletion in 13C, 18O and 2H compared to C3-host plants should be expected for tissues of C3-hemiparasites. However, 2H is counterbalanced by transpiration (2H-depletion) and heterotrophy (2H-enrichment). Progressive 2H-enrichment can be used as a proxy to evaluate carbon gains from hosts.

A Legume Host Benefits More from Arbuscular Mycorrhizal Fungi Than a Grass Host in the Presence of a Root Hemiparasitic Plant

In nature, most plants parasitized by root hemiparasites are also colonized by mutualistic arbuscular mycorrhizal (AM) fungi, highlighting the prevalence of this tripartite interaction. AM colonization is generally found to improve the growth of parasitized legumes but has little impact on grass hosts parasitized by root hemiparasites, and the underlying mechanisms are still unclear. In this study, we conducted a pot experiment to test the influence of AM fungus (Glomus mosseae) on the growth and photosynthesis of leguminous Trifolium repens and gramineous Elymus nutans in the presence of a root hemiparasitic plant (Pedicularis kansuensis). The results showed that inoculation with AM fungi significantly improved the growth performance of parasitized legumes via enhancing their nutrient status and photosynthetic capacity, even though a larger P. kansuensis parasitized the legume host in the AM treatment. In contrast, AM colonization slightly improved the shoot DW of grass hosts by suppressing haustoria formation and the growth of P. kansuensis. Our results demonstrated that legume hosts benefit more from AM inoculation than grass hosts in the presence of hemiparasitic plants, and set out the various mechanisms. This study provides new clues for parsing the tritrophic interaction of AM fungi, parasitic plants, and host plants.

Flora of Ceará, Brazil: Loranthaceae

Abstract This study provides a taxonomic treatment for the species of Loranthaceae in the state of Ceará, Northeastern Brazil. The survey was made based on the previous consultation of virtual herbaria, in loco visits, material loans, and photographs of diagnostic traits sent by herbarium curators. Morphological traits and geographic coordinates of all specimens collected in the State were recorded to prepare the distribution maps, identification key, and taxonomic descriptions for each taxon. A total of 184 specimens (discounting duplicates) from 30 herbaria were studied. Eight species are recorded for Ceará: Passovia pedunculata, Passovia pyrifolia, Psittacanthus cordatus, Psittacanthus dichroos, Psittacanthus eucalyptifolius, Struthanthus marginatus, Struthanthus polyrrhizus, and Struthanthus syringifolius. None are included in the IUCN Red List. However, four of them were collected inside protected areas (i.e., Passovia pedunculata, Psittacanthus cordatus, S. polyrrhizus, and S. syringifolius).

Does phosphorus influence performance of a native hemiparasite and its impact on a native legume?

Phosphorus (P) is an essential plant nutrient and can become limiting in terrestrial ecosystems where parasitic plant:host associations occur. Yet little is known on how P availability influences parasite performance and its impact on hosts. We investigated the performance of the Australian native stem hemiparasite Cassytha pubescens and its impact on the native leguminous shrub Acacia paradoxa in high or low P conditions in a glasshouse experiment. Infected plants had significantly lower total, shoot, root and nodule biomass and shoot:root ratio than uninfected plants, regardless of P supply. The significant negative effect of infection on arbuscular mycorrhizal colonisation of host roots was more severe in the high P treatment. Infection significantly decreased predawn quantum yield of A. paradoxa in low P but not high P conditions. This finding may be due to the parasite-induced significant enrichment of aluminium in host foliage in low P but not high P treatments. A. paradoxa had significantly lower foliar phosphorus concentration [P] and nitrogen concentration in low P than high P conditions. Parasite biomass and photosynthetic performance were unaffected by P, whereas C. pubescens had significantly lower stem [P] in the low P than high P treatment. Parasite carbon isotope composition was significantly higher than that of the host, especially in low P conditions. Our results show that: (a) native parasite growth and its negative impact on growth of this native shrub was unaffected by P supply and (b) soil P conditions may have no influence on stem hemiparasite:host associations in nature.

Implications of mistletoe parasitism for the host metabolome: A new plant identity in the forest canopy

Mistletoe-host systems exemplify an intimate and chronic relationship where mistletoes represent protracted stress for hosts, causing long-lasting impact. Although host changes in morphological and reproductive traits due to parasitism are well known, shifts in their physiological system, altering metabolite concentrations, are less known due to the difficulty of quantification. Here, we use ecometabolomic techniques in the plant-plant interaction, comparing the complete metabolome of the leaves from mistletoe (Viscum album) and needles from their host (Pinus nigra), both parasitized and unparasitized, to elucidate host responses to plant parasitism. Our results show that mistletoe acquires metabolites basically from the primary metabolism of its host and synthesizes its own defence compounds. In response to mistletoe parasitism, pines modify a quarter of their metabolome over the year, making the pine canopy metabolome more homogeneous by reducing the seasonal shifts in top-down stratification. Overall, host pines increase antioxidant metabolites, suggesting oxidative stress, and also increase part of the metabolites required by mistletoe, which act as a permanent sink of host resources. In conclusion, by exerting biotic stress and thereby causing permanent systemic change, mistletoe parasitism generates a new host-plant metabolic identity available in forest canopy, which could have notable ecological consequences in the forest ecosystem.

Endoparasitic plants and fungi show evolutionary convergence across phylogenetic divisions

Endoparasitic plants are the most reduced flowering plants, spending most of their lives as a network of filaments within the tissues of their hosts. Despite their extraordinary life form, we know little about their biology. Research into a few species has revealed unexpected insights, such as the total loss of plastome, the reduction of the vegetative phase to a proembryonic stage, and elevated information exchange between host and parasite. To consolidate our understanding, we review life history, anatomy, and molecular genetics across the four independent lineages of endoparasitic plants. We highlight convergence across these clades and a striking trans-kingdom convergence in life history among endoparasitic plants and disparate lineages of fungi at the molecular and physiological levels. We hypothesize that parasitism of woody plants preselected for the endoparasitic life history, providing parasites a stable host environment and the necessary hydraulics to enable floral gigantism and/or high reproductive output. Finally, we propose a broader view of endoparasitic plants that connects research across disciplines, for example, pollen-pistil and graft incompatibility interactions and plant associations with various fungi. We shine a light on endoparasitic plants and their hosts as under-explored ecological microcosms ripe for identifying unexpected biological processes, interactions and evolutionary convergence.

Correlational nutritional relationships and interactions between expansive holoparasite Orobanche laxissima and woody hosts on metal-rich soils

Plant parasitism by other plants, combined with abiotic environmental stress, offers a unique opportunity to study correlational nutritional relationships in terms of parasite-host interactions and their functional roles in nutrient cycling in ecosystems. Our study analysed the transfer of selected mineral elements, including heavy metals, from soil to different organs in hosts (Punica granatum and Fraxinus angustifolia) and from hosts to the expansive holoparasite (Orobanche laxissima) in cinnamonic soil habitats in Georgia (Caucasus). We also identified other correlated trophic and bioactive effects in the parasite-host relationship. O. laxissima was characterized by a high accumulation tendency for micro- and macroelements, such as K and Ca, and heavy metals, such as Zn, Ni, and Cd. Parasites can reduce the concentration of heavy metals in host tissues owing to this high accumulation tendency. In total, 85 compounds were identified in the examined parasite and its hosts. Despite the distinct phytochemical content of species of the infected host, the parasite produced specific metabolites with dominant phenylethanoid glycosides (PhGs), with acteoside and crenatoside being the primary dominant compounds - ca. 98% of all polyphenols. Polyphenols in parasite specimens that are correlated with Cu and Zn are antagonistic to polyphenols correlated with Fe, Pb, Cr, and Ni. The profile of polyphenols in the host species was both qualitatively and quantitatively distinct from the profile of the compounds in the parasite and between hosts (only acteoside in group PhGs was common between the parasite and Fraxinus host), which indicates the existence of a unique compound biosynthesis pathway in the parasite. Our results demonstrated that the parasite, particularly in its flowers, exhibited higher polyphenol content, antioxidative effects (ABTS-+, DPPH, and FRAP), and inhibitory effects.

Avoiding rather than resisting herbivore attacks is often the first line of plant defence

A common idea is that resisting or blocking herbivore attacks by structural, chemical and molecular means after they have commenced is the first line of plant defence. However, these are all secondary defences, operating only when all the various methods of avoiding attack have failed. The real first line of plant defence from herbivory and herbivore-transmitted pathogens is avoiding such attacks altogether. Several visual, chemical and ‘statistical’ methods (and commonly their combined effects) have been proposed to allow avoidance of herbivore attacks. The visual types are camouflage, masquerade, aposematic coloration of toxic or physically defended plants (including Müllerian/Batesian mimicry), undermining herbivorous insect camouflage, delayed greening, dazzle and trickery coloration, heterophylly that undermines host identification, leaf movements, and signalling that colourful autumn leaves are soon to be shed. The mimicry types include: herbivore damage, insects and other animals, fungal infestation, dead/dry leaves or branches, animal droppings, and stones and soil. Olfactory-based tactics include odour aposematism by poisonous plants, various repelling volatiles, mimicry of faeces and carrion odours, and mimicry of aphid alarm pheromones. The ‘statistical’ methods are mast fruiting, flowering only once in many years and being rare. In addition to the theoretical aspects, understanding these mechanisms may have considerable potential for agricultural or forestry applications.

Plant Parasites under Pressure: Effects of Abiotic Stress on the Interactions between Parasitic Plants and Their Hosts

Parasitic angiosperms, comprising a diverse group of flowering plants, are partially or fully dependent on their hosts to acquire water, mineral nutrients and organic compounds. Some have detrimental effects on agriculturally important crop plants. They are also intriguing model systems to study adaptive mechanisms required for the transition from an autotrophic to a heterotrophic metabolism. No less than any other plant, parasitic plants are affected by abiotic stress factors such as drought and changes in temperature, saline soils or contamination with metals or herbicides. These effects may be attributed to the direct influence of the stress, but also to diminished host availability and suitability. Although several studies on abiotic stress response of parasitic plants are available, still little is known about how abiotic factors affect host preferences, defense mechanisms of both hosts and parasites and the effects of combinations of abiotic and biotic stress experienced by the host plants. The latter effects are of specific interest as parasitic plants pose additional pressure on contemporary agriculture in times of climate change. This review summarizes the existing literature on abiotic stress response of parasitic plants, highlighting knowledge gaps and discussing perspectives for future research and potential agricultural applications.

Genomic reconfiguration in parasitic plants involves considerable gene losses alongside global genome size inflation and gene births

Parasitic plant genomes and transcriptomes reveal numerous genetic innovations, the functional-evolutionary relevance and roles of which open unprecedented research avenues.

Association of putatively adaptive genetic variation with climatic variables differs between a parasite and its host

Parasitism is a pervasive phenomenon in nature with the relationship between species driving evolution in both parasite and host. Due to their host-dependent lifestyle, parasites may adapt to the abiotic environment in ways that differ from their hosts or from free-living relatives; yet rarely has this been assessed. Here, we test two competing hypotheses related to whether putatively adaptive genetic variation in a specialist mistletoe associates with the same, or different, climatic variables as its host species. We sampled 11 populations of the specialist mistletoe Amyema gibberula var. tatei (n = 154) and 10 populations of its associated host Hakea recurva subsp. recurva (n = 160). Reduced-representation sequencing was used to obtain genome-wide markers and putatively adaptive variation detected using genome scan methods. Climate associations were identified using generalized dissimilarity modelling, and these were mapped geographically to visualize the spatial patterns of genetic composition. Our results supported the hypothesis of parasites and host species responding differently to climatic variables. Temperature was relatively more important in predicting allelic turnover in the specialist mistletoe while precipitation was more important for the host. This suggests that parasitic plants and host species may respond differently to selective pressures, potentially as a result of differing nutrient acquisition strategies. Specifically, mistletoes acquire water from hosts (rather than the abiotic environment), which may provide a buffer to precipitation as a selective pressure. This work deepens and complements the physiological and other ecological studies of adaptation and provides a window into the evolutionary processes that underlie previously observed phenomena. Applying these methods to a comparative study in a host-parasite system has also highlighted factors that affect the study of selection pressure on nonmodel organisms, such as differing adaptation rates and lack of reference genomes.