Parasitic dodder expresses an arsenal of secreted cellulases with multi-substrate specificity during host invasion.

Cuscuta campestris is a common and problematic parasitic plant which relies on haustoria to connect to and siphon nutrients from host plants. Glycoside hydrolase family 9 (GH9) cellulases (EC 3.2.1.4) play critical roles in plant cell wall biosynthesis and disassembly, but their roles during Cuscuta host invasion remains underexplored. In this study, we identified 22 full-length GH9 cellulase genes in C. campestris genome, which encoded fifteen secreted and seven membrane-anchored cellulases that showed distinct phylogenetic relationships. Expression profiles suggested that some of the genes are involved in biosynthesis and remodeling of the parasite's cell wall during haustoriogenesis, while other genes encoding secreted B- and C-type cellulases are tentatively associated with degrading host cell walls during invasion. Transcriptomic data in a host-free system and in the presence of susceptible or partially resistant tomato hosts, showed for especially GH9B7, GH9B11 and GH9B12 a shift in expression profiles in the presence of hosts, being more highly expressed during host attachment, indicating that Cuscuta can tune cellulase expression in response to a host. Functional analyses of recombinant B- and C-type cellulases showed endoglucanase activities over wide pH and temperature conditions, and activities towards multiple cellulose and hemicellulose substrates. These findings improve our understanding of host cell wall disassembly by Cuscuta, and cellulase activity towards broad substrate range potentially explain its wide host range. This is the first study to provide a broad biochemical insight into Cuscuta GH9 cellulases, which based on our study may have potential applications in industrial bioprocessing.

The soil microbiome modulates the sorghum root metabolome and cellular traits with a concomitant reduction of Striga infection.

Sorghum bicolor is among the most important cereals globally and a staple crop for smallholder farmers in sub-Saharan Africa. Approximately 20% of sorghum yield is lost annually in Africa due to infestation with the root parasitic weed Striga hermonthica. Existing Striga management strategies are not singularly effective and integrated approaches are needed. Here, we demonstrate the functional potential of the soil microbiome to suppress Striga infection in sorghum. We associate this suppression with microbiome-mediated induction of root endodermal suberization and aerenchyma formation and with depletion of haustorium-inducing factors, compounds required for the initial stages of Striga infection. We further identify specific bacterial taxa that trigger the observed Striga-suppressive traits. Collectively, our study describes the importance of the soil microbiome in the early stages of root infection by Striga and pinpoints mechanisms of Striga suppression. These findings open avenues to broaden the effectiveness of integrated Striga management practices.

Border Control: Manipulation of the Host-Pathogen Interface by Perihaustorial Oomycete Effectors.

Filamentous plant pathogens, including fungi and oomycetes, cause some of the most devastating plant diseases. These organisms serve as ideal models for understanding the intricate molecular interplay between plants and the invading pathogens. Filamentous pathogens secrete effector proteins via haustoria, specialized structures for infection and nutrient uptake, to suppress the plant immune response and to reprogram plant metabolism. Recent advances in cell biology have provided crucial insights into the biogenesis of the extrahaustorial membrane and the redirection of host endomembrane trafficking toward this interface. Functional studies have shown that an increasing number of oomycete effectors accumulate at the perihaustorial interface to subvert plant focal immune responses, with a particular convergence on targets involved in host endomembrane trafficking. In this review, we summarize the diverse mechanisms of perihaustorial effectors from oomycetes and pinpoint pressing questions regarding their role in manipulating host defense and metabolism at the haustorial interface. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

CRISPR gene editing to improve crop resistance to parasitic plants.

Parasitic plants pose a significant threat to global agriculture, causing substantial crop losses and hampering food security. In recent years, CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) gene-editing technology has emerged as a promising tool for developing resistance against various plant pathogens. Its application in combating parasitic plants, however, remains largely unexplored. This review aims to summarise current knowledge and research gaps in utilising CRISPR to develop resistance against parasitic plants. First, we outline recent improvements in CRISPR gene editing tools, and what has been used to combat various plant pathogens. To realise the immense potential of CRISPR, a greater understanding of the genetic basis underlying parasitic plant-host interactions is critical to identify suitable target genes for modification. Therefore, we discuss the intricate interactions between parasitic plants and their hosts, highlighting essential genes and molecular mechanisms involved in defence response and multilayer resistance. These include host resistance responses directly repressing parasitic plant germination or growth and indirectly influencing parasitic plant development via manipulating environmental factors. Finally, we evaluate CRISPR-mediated effectiveness and long-term implications for host resistance and crop improvement, including inducible resistance response and tissue-specific activity. In conclusion, this review highlights the challenges and opportunities CRISPR technology provides to combat parasitic plants and provides insights for future research directions to safeguard global agricultural productivity.

Profiling of phenolic acids, flavonoids, terpenoids, and steroid derivatives in coconut (Cocos nucifera L.) haustorium.

Coconut haustorium (CH) is formed inside coconut shell during coconut germination. This study aimed to investigate the compositions and contents of CH phytochemicals. Phytochemical compositions and contents in CH were analyzed by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) and spectrophotometrical method. Five phenolic acids and four flavonoids were identified in CH. Ferulic acid and myricetin were the most abundant among phenolic acids and flavonoids identified in CH, respectively. Nepetariaside and 1-methylene-5α-androstan-3α-ol-17-one glucuronide were the most abundant terpenoids and steroid derivatives identified in CH, respectively. To our knowledge, this study screened several classes of phytochemicals in CH for the first. Terpenoids and steroid derivatives were likely to be more major phytochemicals than phenolic acids and flavonoids in CH. The functionality of CH itself and the compounds found in CH might be utilized in functional foods or cosmetics. Supplementary Information: The online version contains supplementary material available at 10.1007/s10068-023-01300-6.

Developing for nutrient uptake: Induced organogenesis in parasitic plants and root nodule symbiosis.

Plants have evolved diverse strategies to meet their nutritional needs. Parasitic plants employ haustoria, specialized structures that facilitate invasion of host plants and nutrient acquisition. Legumes have adapted to nitrogen-limited conditions by developing nodules that accommodate nitrogen-fixing rhizobia. The formation of both haustoria and nodules is induced by signals originating from the interacting organisms, namely host plants and rhizobial bacteria, respectively. Emerging studies showed that both organogenesis crucially involves plant hormones such as auxin, cytokinins, and ethylene and also integrate nutrient availability, particularly nitrogen. In this review, we discuss recent advances on hormonal and environmental control of haustoria and nodules development with side-by-side comparison. These underscore the remarkable plasticity of plant organogenesis.

Traffic Control: Subversion of Plant Membrane Trafficking by Pathogens.

Membrane trafficking pathways play a prominent role in plant immunity. The endomembrane transport system coordinates membrane-bound cellular organelles to ensure that immunological components are utilized effectively during pathogen resistance. Adapted pathogens and pests have evolved to interfere with aspects of membrane transport systems to subvert plant immunity. To do this, they secrete virulence factors known as effectors, many of which converge on host membrane trafficking routes. The emerging paradigm is that effectors redundantly target every step of membrane trafficking from vesicle budding to trafficking and membrane fusion. In this review, we focus on the mechanisms adopted by plant pathogens to reprogram host plant vesicle trafficking, providing examples of effector-targeted transport pathways and highlighting key questions for the field to answer moving forward.

The plant vampire diaries: a historic perspective on Cuscuta research.

The angiosperm genus Cuscuta lives as an almost achlorophyllous root- and leafless holoparasite and has therefore occupied scientists for more than a century. The 'evolution' of Cuscuta research started with early studies that established the phylogenetic framework for this unusual genus. It continued to produce groundbreaking cytological, morphological, and physiological insight throughout the second half of the 20th century and culminated in the last two decades in exciting discoveries regarding the molecular basis of Cuscuta parasitism that were facilitated by the modern 'omics' tools and traceable fluorescent marker technologies of the 21st century. This review will show how present activities are inspired by those past breakthroughs. It will describe significant milestones and recurring themes of Cuscuta research and connect these to the remaining as well as newly evolving questions and future directions in this research field that is expected to sustain its strong growth in the future.

Germinating seedlings and mature shoots of Cuscuta campestris respond differently to light stimuli during parasitism but not during circumnutation.

Seedlings of the parasitic plant genus Cuscuta (dodder) locate hosts by circumnutation, coil around the host near soil level and form a haustorium, establishing a primary parasitism beneath the canopy. Mature shoots elongating from the parasitic region parasitize other hosts on the upper surfaces of their canopy. Although parasitism by dodder is stimulated by blue and far-red light, and inhibited by red light, the responses to light signals during the developmental stages are not comprehensively understood. Therefore, we compared the effects of different types of light on both circumnutation and parasitism by germinating seedlings and mature shoots of Cuscuta campestris. Seedlings established parasitism under blue and far-red light, but not under red light, as has been reported repeatedly. By contrast, mature shoots exhibited coiling around the host and haustoria formation even under a red light as well as under blue and far-red light. These findings indicate that C. campestris modified its response to red light during the transition from young seedlings to mature shoots, facilitating parasitism. Light quality did not affect the circumnutation of either seedlings or mature shoots, indicating that circumnutation and the coiling movement that leads to parasitism were regulated by different environmental signals.

Protein Profiling of Psittacanthus calyculatus during Mesquite Infection.

Psittacanthus calyculatus is a hemiparasite mistletoe that represents an ecological problem due to the impacts caused to various tree species of ecological and commercial interest. Although the life cycle for the Psittacanthus genus is well established in the literature, the development stages and molecular mechanism implicated in P. calyculatus host infection are poorly understood. In this study, we used a manageable infestation of P. laevigata with P. calyculatus to clearly trace the infection, which allowed us to describe five phenological infective stages of mistletoe on host tree branches: mature seed (T1), holdfast formation (T2), haustorium activation (T3), haustorium penetration (T4), and haustorium connection (T5) with the host tree. Proteomic analyses revealed proteins with a different accumulation and cellular processes in infective stages. Activities of the cell wall-degrading enzymes cellulase and ß-1,4-glucosidase were primarily active in haustorium development (T3), while xylanase, endo-glucanase, and peptidase were highly active in the haustorium penetration (T4) and xylem connection (T5). Patterns of auxins and cytokinin showed spatial concentrations in infective stages and moreover were involved in haustorium development. These results are the first evidence of proteins, cell wall-degrading enzymes, and phytohormones that are involved in early infection for the Psittacanthus genus, and thus represent a general infection mechanism for other mistletoe species. These results could help to understand the molecular dialogue in the establishment of P. calyculatus parasitism.

Genomic and Epigenomic Mechanisms of the Interaction between Parasitic and Host Plants.

Parasitic plants extract nutrients from the other plants to finish their life cycle and reproduce. The control of parasitic weeds is notoriously difficult due to their tight physical association and their close biological relationship to their hosts. Parasitic plants differ in their susceptible host ranges, and the host species differ in their susceptibility to parasitic plants. Current data show that adaptations of parasitic plants to various hosts are largely genetically determined. However, multiple cases of rapid adaptation in genetically homogenous parasitic weed populations to new hosts strongly suggest the involvement of epigenetic mechanisms. Recent progress in genome-wide analyses of gene expression and epigenetic features revealed many new molecular details of the parasitic plants' interactions with their host plants. The experimental data obtained in the last several years show that multiple common features have independently evolved in different lines of the parasitic plants. In this review we discuss the most interesting new details in the interaction between parasitic and host plants.

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.

Emerging technologies for the chemical control of root parasitic weeds.

Parasitic plants in the Orobanchaceae family include devastating weed species, such as Striga, Orobanche, and Phelipanche, which parasitize major crops, drastically reduces crop yields and cause economic losses of over a billion US dollars worldwide. Advances in basic research on molecular and cellular processes responsible for parasitic relationships has now achieved steady progress through advances in genome analysis, biochemical analysis and structural biology. On the basis of these advances it is now possible to develop chemicals that control parasitism and reduce agricultural damage. In this review we summarized the recent development of chemicals that can control each step of parasitism from strigolactone biosynthesis in host plants to haustorium formation.

Cuscuta species: Model organisms for haustorium development in stem holoparasitic plants.

Parasitic plants are notorious for causing serious agricultural losses in many countries. Specialized intrusive organs, haustoria, confer on parasitic plants the ability to acquire water and nutrients from their host plants. Investigating the mechanism involved in haustorium development not only reveals the fascinating mystery of how autotrophic plants evolved parasitism but also provides the foundation for developing more effective methods to control the agricultural damage caused by parasitic plants. Cuscuta species, also known as dodders, are one of the most well-known and widely spread stem holoparasitic plants. Although progress has been made recently in understanding the evolution and development of haustoria in root parasitic plants, more and more studies indicate that the behaviors between root and stem haustorium formation are distinct, and the mechanisms involved in the formation of these organs remain largely unknown. Unlike most endoparasites and root holoparasitic plants, which have high host-specificity and self- or kin-recognition to avoid forming haustoria on themselves or closely related species, auto-parasitism and hyper-parasitism are commonly observed among Cuscuta species. In this review, we summarize the current understanding of haustorium development in dodders and the unique characteristics of their parasitizing behaviors. We also outline the advantages of using Cuscuta species as model organisms for haustorium development in stem holoparasitic plants, the current unknown mysteries and limitations in the Cuscuta system, and potential future research directions to overcome these challenges.

Analysis of Rac/Rop Small GTPase Family Expression in Santalum album L. and Their Potential Roles in Drought Stress and Hormone Treatments.

Plant-specific Rac/Rop small GTPases, also known as Rop, belong to the Rho subfamily. Rac proteins can be divided into two types according to their C-terminal motifs: Type I Rac proteins have a typical CaaL motif at the C-terminal, whereas type II Rac proteins lack this motif but retain a cysteine-containing element for membrane anchoring. The Rac gene family participates in diverse signal transduction events, cytoskeleton morphogenesis, reactive oxygen species (ROS) production and hormone responses in plants as molecular switches. S. album is a popular semiparasitic plant that absorbs nutrients from the host plant through the haustoria to meet its own growth and development needs. Because the whole plant has a high use value, due to the high production value of its perfume oils, it is known as the "tree of gold". Based on the full-length transcriptome data of S. album, nine Rac gene members were named SaRac1-9, and we analyzed their physicochemical properties. Evolutionary analysis showed that SaRac1-7, AtRac1-6, AtRac9 and AtRac11 and OsRac5, OsRacB and OsRacD belong to the typical plant type I Rac/Rop protein, while SaRac8-9, AtRac7, AtRac8, AtRac10 and OsRac1-4 belong to the type II Rac/ROP protein. Tissue-specific expression analysis showed that nine genes were expressed in roots, stems, leaves and haustoria, and SaRac7/8/9 expression in stems, haustoria and roots was significantly higher than that in leaves. The expression levels of SaRac1, SaRac4 and SaRac6 in stems were very low, and the expression levels of SaRac2 and SaRac5 in roots and SaRac2/3/7 in haustoria were very high, which indicated that these genes were closely related to the formation of S. album haustoria. To further analyze the function of SaRac, nine Rac genes in sandalwood were subjected to drought stress and hormone treatments. These results establish a preliminary foundation for the regulation of growth and development in S. album by SaRac.

The haustorium: The root of biotrophic fungal pathogens.

Biotrophic plant pathogenic fungi are among the dreadful pathogens that continuously threaten the production of economically important crops. The interaction of biotrophic fungal pathogens with their hosts necessitates the development of unique infection mechanisms and involvement of various virulence-associated components. Biotrophic plant pathogenic fungi have an exceptional lifestyle that supports nutrient acquisition from cells of a living host and are fully dependent on the host for successful completion of their life cycle. The haustorium, a specialized infection structure, is the key organ for biotrophic fungal pathogens. The haustorium is not only essential in the uptake of nutrients without killing the host, but also in the secretion and delivery of effectors into the host cells to manipulate host immune system and defense responses and reprogram the metabolic flow of the host. Although there is a number of unanswered questions in this area yet, results from various studies indicate that the haustorium is the root of biotrophic fungal pathogens. This review provides an overview of current knowledge of the haustorium, its structure, composition, and functions, which includes the most recent haustorial transcriptome studies.

Cytokinins Induce Prehaustoria Coordinately with Quinone Signals in the Parasitic Plant Striga hermonthica.

Orobanchaceae parasitic plants are major threats to global food security, causing severe agricultural damage worldwide. Parasitic plants derive water and nutrients from their host plants through multicellular organs called haustoria. The formation of a prehaustorium, a primitive haustorial structure, is provoked by host-derived haustorium-inducing factors (HIFs). Quinones, including 2,6-dimethoxy-p-benzoquinone (DMBQ), are of the most potent HIFs for various species in Orobanchaceae, but except non-photosynthetic holoparasites, Phelipanche and Orobanche spp. Instead, cytokinin (CK) phytohormones were reported to induce prehaustoria in Phelipanche ramosa. However, little is known about whether CKs act as HIFs in the other parasitic species to date. Moreover, the signaling pathways for quinones and CKs in prehaustorium induction are not well understood. This study shows that CKs act as HIFs in the obligate parasite Striga hermonthica but not in the facultative parasite Phtheirospermum japonicum. Using chemical inhibitors and marker gene expression analysis, we demonstrate that CKs activate prehaustorium formation through a CK-specific signaling pathway that overlaps with the quinone HIF pathway at downstream in S. hermonthica. Moreover, host root exudates activated S. hermonthica CK biosynthesis and signaling genes, and DMBQ and CK inhibitors perturbed the prehaustorium-inducing activity of exudates, indicating that host root exudates include CKs. Our study reveals the importance of CKs for prehaustorium formation in obligate parasitic plants.

Regulatory Modules Involved in the Degradation and Modification of Host Cell Walls During Cuscuta campestris Invasion.

Haustoria of parasitic plants have evolved sophisticated traits to successfully infect host plants. The degradation and modification of host cell walls enable the haustorium to effectively invade host tissues. This study focused on two APETALA2/ETHYLENE RESPONSE FACTOR (ERF) genes and a set of the cell wall enzyme genes principally expressed during the haustorial invasion of Cuscuta campestris Yuncker. The orthogroups of the TF and cell wall enzyme genes have been implicated in the cell wall degradation and modification activities in the abscission of tomatoes, which are currently the phylogenetically closest non-parasitic model species of Cuscuta species. Although haustoria are generally thought to originate from root tissues, our results suggest that haustoria have further optimized invasion potential by recruiting regulatory modules from other biological processes.

Molecular Processes of Dodder Haustorium Formation on Host Plant under Low Red/Far Red (R/FR) Irradiation.

Low R/FR irradiation can promote dodder haustorium formation on the host plant; however, the mechanisms underlying the process are still unknown. In this study, we compared the transcriptomic data during the formation of haustorium of Cuscuta chinensis on host plant Arabidopsisthaliana under low (R/FR = 0.1) versus high (R/FR = 0.2) R/FR irradiation at 12 h, 24 h and 72 h time points. The results show that low R/FR radiation significantly promoted the entanglement and haustorium formation. Transcriptome analysis showed that during the early stage of haustorium formation, low R/FR radiation significantly up-regulated ARR-A related genes and down-regulated peroxidase related genes compared with high R/FR radiation. Meanwhile, during the middle stage of haustorium formation, low R/FR treatment significantly increased the expression of genes related to pectinesterase (PE), polygalacturonase (PG) and pectin lyase (Pel) production, while, during the late stage of haustorium formation, peroxidase (Prx)-related genes were differentially expressed under different R/FR treatments. Overall, our findings show that a low R/FR ratio promotes the parasitism of C. chinensis through plant hormone signal transduction and cell wall degradation pathways. This study provides a basis for the control of parasitic plants.