Feeding cells induced by phytoparasitic nematodes require γ-tubulin ring complex for microtubule reorganization

An ex vitro hairy root system from petioles of detached soybean leaves for in planta screening of target genes and CRISPR strategies associated with nematode bioassays

MAIN CONCLUSION

The ex vitro hairy root system from petioles of detached soybean leaves allows the functional validation of genes using classical transgenesis and CRISPR strategies (e.g., sgRNA validation, gene activation) associated with nematode bioassays. Agrobacterium rhizogenes-mediated root transformation has been widely used in soybean for the functional validation of target genes in classical transgenesis and single-guide RNA (sgRNA) in CRISPR-based technologies. Initial data showed that in vitro hairy root induction from soybean cotyledons and hypocotyls were not the most suitable strategies for simultaneous performing genetic studies and nematode bioassays. Therefore, an ex vitro hairy root system was developed for in planta screening of target molecules during soybean parasitism by root-knot nematodes (RKNs). Applying this method, hairy roots were successfully induced by A. rhizogenes from petioles of detached soybean leaves. The soybean GmPR10 and GmGST genes were then constitutively overexpressed in both soybean hairy roots and tobacco plants, showing a reduction in the number of Meloidogyne incognita-induced galls of up to 41% and 39%, respectively. In addition, this system was evaluated for upregulation of the endogenous GmExpA and GmExpLB genes by CRISPR/dCas9, showing high levels of gene activation and reductions in gall number of up to 58.7% and 67.4%, respectively. Furthermore, morphological and histological analyses of the galls were successfully performed. These collective data validate the ex vitro hairy root system for screening target genes, using classical overexpression and CRISPR approaches, directly in soybean in a simple manner and associated with nematode bioassays. This system can also be used in other root pathosystems for analyses of gene function and studies of parasite interactions with plants, as well as for other purposes such as studies of root biology and promoter characterization.

Morphological characterization reveals new insights into giant cell development of Meloidogyne graminicola on rice

Three types of nematode-feeding sites (NFSs) caused by M. graminicola on rice were suggested, and the NFS polarized expansion stops before the full NFS maturation that occurs at adult female stage. Root-knot nematodes, Meloidogyne spp., secrete effectors and recruit host genes to establish their feeding sites giant cells, ensuring their nutrient acquisition. There is still a limited understanding of the mechanism underlying giant cell development. Here, the three-dimensional structures of M. graminicola-caused nematode-feeding sites (NFSs) on rice as well as changes in morphological features and cytoplasm density of the giant cells (GCs) during nematode parasitism were reconstructed and characterized by confocal microscopy and the Fiji software. Characterization of morphological features showed that three types of M. graminicola-caused NFSs, type I-III, were detected during parasitism at the second juvenile (J2), the third juvenile (J3), the fourth juvenile (J4) and adult female stages. Type I is the majority at all stages and type II develops into type I at J3 stage marked by its longitudinal growth. Meanwhile, NFSs underwent polarized expansion, where the lateral and longitudinal expansion ceased at later parasitic J2 stage and the non-feeding J4 stage, respectively. The investigation of giant cell cytoplasm density indicates that it reaches a peak at the midpoint of early parasitic J2 and adult female stages. Our data suggest the formation of three types of NFSs caused by M. graminicola on rice and the NFS polarized expansion stopping before full NFS maturation, which provides unprecedented spatio-temporal characterization of development of giant cells caused by a root-knot nematode.

Pyramiding dsRNAs increases phytonematode tolerance in cotton plants

Host-derived suppression of nematode essential genes decreases reproduction of Meloidogyne incognita in cotton. Root-knot nematodes (RKN) represent one of the most damaging plant-parasitic nematode genera worldwide. RNAi-mediated suppression of essential nematode genes provides a novel biotechnological strategy for the development of sustainable pest-control methods. Here, we used a Host Induced Gene Silencing (HIGS) approach by stacking dsRNA sequences into a T-DNA construct to target three essential RKN genes: cysteine protease (Mi-cpl), isocitrate lyase (Mi-icl), and splicing factor (Mi-sf), called dsMinc1, driven by the pUceS8.3 constitutive soybean promoter. Transgenic dsMinc1-T₄ plants infected with Meloidogyne incognita showed a significant reduction in gall formation (57-64%) and egg masses production (58-67%), as well as in the estimated reproduction factor (60-78%), compared with the susceptible non-transgenic cultivar. Galls of the RNAi lines are smaller than the wild-type (WT) plants, whose root systems exhibited multiple well-developed root swellings. Transcript levels of the three RKN-targeted genes decreased 13- to 40-fold in nematodes from transgenic cotton galls, compared with those from control WT galls. Finally, the development of non-feeding males in transgenic plants was 2-6 times higher than in WT plants, indicating a stressful environment for nematode development after RKN gene silencing. Data strongly support that HIGS of essential RKN genes is an effective strategy to improve cotton plant tolerance. This study presents the first application of dsRNA sequences to target multiple genes to promote M. incognita tolerance in cotton without phenotypic penalty in transgenic plants.

Plasmodesmata play pivotal role in sucrose supply to Meloidogyne graminicola-caused giant cells in rice

On infection, plant-parasitic nematodes establish feeding sites in roots from which they take up carbohydrates among other nutrients. Knowledge on how carbohydrates are supplied to the nematodes' feeding sites is limited. Here, gene expression analyses showed that RNA levels of OsSWEET11 to OsSWEET15 were extremely low in both Meloidogyne graminicola (Mg)-caused galls and noninoculated roots. All the rice sucrose transporter genes, OsSUT1 to OsSUT5, were either down-regulated in Mg-caused galls compared with noninoculated rice roots or had very low transcript abundance. OsSUT1 was the only gene up-regulated in galls, at 14 days postinoculation (dpi), after being highly down-regulated at 3 and 7 dpi. OsSUT4 was down-regulated at 3 dpi. No noticeable OsSUTs promoter activities were detected in Mg-caused galls of pOsSUT1 to -5::GUS rice lines. Loading experiments with carboxyfluorescein diacetate (CFDA) demonstrated that symplastic connections exist between phloem and Mg-caused giant cells (GCs). According to data from OsGNS5- and OsGSL2-overexpressing rice plants that had decreased and increased callose deposition, respectively, callose negatively affected Mg parasitism and sucrose supply to Mg-caused GCs. Our results suggest that plasmodesmata-mediated sucrose transport plays a pivotal role in sucrose supply from rice root phloem to Mg-caused GCs, and OsSWEET11 to -15 and OsSUTs are not major players in it, although further functional analysis is needed for OsSUT1 and OsSUT4.

Imaging Mass Spectrometry of Endogenous Polypeptides and Secondary Metabolites from Galls Induced by Root-Knot Nematodes in Tomato Roots

Nematodes are devastating pests that infect most cultivated plant species and cause considerable agricultural losses worldwide. The understanding of metabolic adjustments induced during plant-nematode interaction is crucial to generate resistant plants or to select more efficient molecules to fight against this pest. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) has been used herein for in situ detection and mapping endogenous polypeptides and secondary metabolites from nematode-induced gall tissue. One of the major critical features of this technique is sample preparation; mainly, the generation of intact sections of plant cells with their rigid cell walls and vacuolated cytoplasm. Our experimental settings allowed us to obtain sections without contamination of exogenous ions or diffusion of molecules and to map the differential presence of low and high molecular weight ions in uninfected roots compared with nematode-induced galls. We predict the presence of lipids in both uninfected roots and galls, which was validated by MALDI time-of-flight tandem mass spectrometry and high-resolution mass spectrometry analysis of lipid extracts. Based on the isotopic ion distribution profile, both esters and glycerophospholipids were predicted compounds and may be playing an important role in gall development. Our results indicate that the MALDI-MSI technology is a promising tool to identify secondary metabolites as well as peptides and proteins in complex plant tissues like galls to decipher molecular processes responsible for infection and maintenance of these feeding sites during nematode parasitism.

Expression of both Arabidopsis γ-tubulin genes is essential for development of a functional syncytium induced by Heterodera schachtii

After initial up-regulation, expression of TUBG1 and TUBG2 is significantly down-regulated in mature syncytia, but lack of expression of either of γ-tubulin genes reduces numbers of nematode infections and developing females. Infective second stage juveniles of sedentary plant parasitic nematode Heterodera schachtii invade the root vascular tissue and induce a feeding site, named syncytium, formed as a result of cell hypertrophy and partial cell wall dissolution leading to a multinucleate state. Syncytium formation and maintenance involves a molecular interplay between the plant host and the developing juveniles leading to rearrangements and fragmentation of the plant cytoskeleton. In this study, we investigated the role of two Arabidopsis γ-tubulin genes (TUBG1 and TUBG2), involved in MTs nucleation during syncytium development. Expression analysis revealed that both γ-tubulin's transcript levels changed during syncytium development and after initial up-regulation (1-3 dpi) they were significantly down-regulated in 7, 10 and 15 dpi syncytia. Moreover, TUBG1 and TUBG2 showed distinct immunolocalization patterns in uninfected roots and syncytia. Although no severe changes in syncytium anatomy and ultrastructure in tubg1-1 and tubg2-1 mutants were observed compared to syncytia induced in wild-type plants, nematode infection assays revealed reduced numbers of infecting juveniles and developed female nematodes in mutant lines. Our results indicate that the expression of both TUBG1 and TUBG2 genes, although generally down-regulated in mature syncytia, is essential for successful root infection, development of functional syncytium and nematode maturation.

The root-knot nematode effector MiPFN3 disrupts plant actin filaments and promotes parasitism

Root-knot nematodes secrete effectors that manipulate their host plant cells so that the nematode can successfully establish feeding sites and complete its lifecycle. The root-knot nematode feeding structures, their “giant cells,” undergo extensive cytoskeletal remodeling. Previous cytological studies have shown the cytoplasmic actin within the feeding sites looks diffuse. In an effort to study root-knot nematode effectors that are involved in giant cell organogenesis, we have identified a nematode effector called MiPFN3 (Meloidogyne incognita Profilin 3). MiPFN3 is transcriptionally up-regulated in the juvenile stage of the nematode. In situ hybridization experiments showed that MiPFN3 transcribed in the nematode subventral glands, where it can be secreted by the nematode stylet into the plant. Moreover, Arabidopsis plants that heterologously expressed MiPFN3 were more susceptible to root-knot nematodes, indicating that MiPFN3 promotes nematode parasitism. Since profilin proteins can bind and sequester actin monomers, we investigated the function of MiPFN3 in relation to actin. Our results show that MiPFN3 suppressed the aberrant plant growth phenotype caused by the misexpression of reproductive actin (AtACT1) in transgenic plants. In addition, it disrupted actin polymerization in an in vitro assay, and it reduced the filamentous actin network when expressed in Arabidopsis protoplasts. Over a decade ago, cytological studies showed that the cytoplasmic actin within nematode giant cells looked fragmented. Here we provide the first evidence that the nematode is secreting an effector that has significant, direct effects on the plant’s actin cytoskeleton.

Root-knot nematodes are microscopic plant pests that infect plant roots and significantly reduce yields of many crop plants. The nematodes enter the plant roots and modify plant cells into complex, multinuclear feeding sites called giant cells. The formation and maintenance of giant cells is critical to nematode survival. During giant cell organogenesis, the progenitor plant cells undergo many morphological changes, including a re-organization of the cytoplasmic actin cytoskeleton. As a result, the giant cell cytoplasmic actin appears fragmented and disorganized. Plant cells can regulate their actin filament assembly, in part, through the expression of actin binding proteins such as profilins. Here we show that infectious nematode juveniles express a profilin called MiPFN3. Expression of MiPFN3 in Arabidopsis plants made the plants more susceptible to root-knot nematodes, indicating that MiPFN3 acts as an effector that aids parasitism. We show evidence that the expression MiPFN3 in plant cells causes the fragmentation of plant actin filaments. The work here demonstrates that nematode effector MiPFN3 can directly affect plant actin filaments, whose reorganization is necessary for giant cell formation.

Smart Parasitic Nematodes Use Multifaceted Strategies to Parasitize Plants

Nematodes are omnipresent in nature including many species which are parasitic to plants and cause enormous economic losses in various crops. During the process of parasitism, sedentary phytonematodes use their stylet to secrete effector proteins into the plant cells to induce the development of specialized feeding structures. These effectors are used by the nematodes to develop compatible interactions with plants, partly by mimicking the expression of host genes. Intensive research is going on to investigate the molecular function of these effector proteins in the plants. In this review, we have summarized which physiological and molecular changes occur when endoparasitic nematodes invade the plant roots and how they develop a successful interaction with plants using the effector proteins. We have also mentioned the host genes which are induced by the nematodes for a compatible interaction. Additionally, we discuss how nematodes modulate the reactive oxygen species (ROS) and RNA silencing pathways in addition to post-translational modifications in their own favor for successful parasitism in plants.

Application of Nuclear Volume Measurements to Comprehend the Cell Cycle in Root-Knot Nematode-Induced Giant Cells

Root-knot nematodes induce galls that contain giant-feeding cells harboring multiple enlarged nuclei within the roots of host plants. It is recognized that the cell cycle plays an essential role in the set-up of a peculiar nuclear organization that seemingly steers nematode feeding site induction and development. Functional studies of a large set of cell cycle genes in transgenic lines of the model host Arabidopsis thaliana have contributed to better understand the role of the cell cycle components and their implication in the establishment of functional galls. Mitotic activity mainly occurs during the initial stages of gall development and is followed by an intense endoreduplication phase imperative to produce giant-feeding cells, essential to form vigorous galls. Transgenic lines overexpressing particular cell cycle genes can provoke severe nuclei phenotype changes mainly at later stages of feeding site development. This can result in chaotic nuclear phenotypes affecting their volume. These aberrant nuclear organizations are hampering gall development and nematode maturation. Herein we report on two nuclear volume assessment methods which provide information on the complex changes occurring in nuclei during giant cell development. Although we observed that the data obtained with AMIRA tend to be more detailed than Volumest (Image J), both approaches proved to be highly versatile, allowing to access 3D morphological changes in nuclei of complex tissues and organs. The protocol presented here is based on standard confocal optical sectioning and 3-D image analysis and can be applied to study any volume and shape of cellular organelles in various complex biological specimens. Our results suggest that an increase in giant cell nuclear volume is not solely linked to increasing ploidy levels, but might result from the accumulation of mitotic defects.

Poplar-Root Knot Nematode Interaction: A Model for Perennial Woody Species

Plant root-knot nematode (RKN) interaction studies are performed on several host plant models. Though RKN interact with trees, no perennial woody model has been explored so far. Here, we show that poplar (Populus tremula × P. alba) grown in vitro is susceptible to Meloidogyne incognita, allowing this nematode to penetrate, to induce feeding sites, and to successfully complete its life cycle. Quantitative reverse transcription-polymerase chain reaction analysis was performed to study changes in poplar gene expression in galls compared with noninfected roots. Three genes (expansin A, histone 3.1, and asparagine synthase), selected as gall development marker genes, followed, during poplar-nematode interaction, a similar expression pattern to what was described for other plant hosts. Downregulation of four genes implicated in the monolignol biosynthesis pathway was evidenced in galls, suggesting a shift in the phenolic profile within galls developed on poplar roots. Raman microspectroscopy demonstrated that cell walls of giant cells were not lignified but mainly composed of pectin and cellulose. The data presented here suggest that RKN exercise conserved strategies to reproduce and to invade perennial plant species and that poplar is a suitable model host to study specific traits of tree-nematode interactions.

In Vivo Imaging of Microtubule Organization in Dividing Giant Cell

Mitosis which is a major step during plant development can also be observed in physiopathological conditions. During the compatible interaction between the root-knot nematode Meloidogyne incognita and its host Arabidopsis, the pathogen induce through repeated divisions without complete cytokinesis the formation of hypertrophied and multinucleate feeding cells, named giant cells. Due to the presence of hypertrophied plant cell material surrounding the giant cells, classical live cell imaging gave therefore very poor resolution. Here, we describe a protocol which allows the in vivo observation of the mitotic apparatus in developing giant cells using confocal imaging of vibrosliced tissues. This approach can also be used to visualize in vivo other cellular processes occurring in different steps of giant cells.

Gall-forming root-knot nematodes hijack key plant cellular functions to induce multinucleate and hypertrophied feeding cells

Among plant-parasitic nematodes, the root-knot nematodes (RKNs) of the Meloidogyne spp. are the most economically important genus. RKN are root parasitic worms able to infect nearly all crop species and have a wide geographic distribution. During infection, RKNs establish and maintain an intimate relationship with the host plant. This includes the creation of a specialized nutritional structure composed of multinucleate and hypertrophied giant cells, which result from the redifferentiation of vascular root cells. Giant cells constitute the sole source of nutrients for the nematode and are essential for growth and reproduction. Hyperplasia of surrounding root cells leads to the formation of the gall or root-knot, an easily recognized symptom of plant infection by RKNs. Secreted effectors produced in nematode salivary glands and injected into plant cells through a specialized feeding structure called the stylet play a critical role in the formation of giant cells. Here, we describe the complex interactions between RKNs and their host plants. We highlight progress in understanding host plant responses, focusing on how RKNs manipulate key plant processes and functions, including cell cycle, defence, hormones, cellular scaffold, metabolism and transport.

Phenotyping nematode feeding sites: three-dimensional reconstruction and volumetric measurements of giant cells induced by root-knot nematodes in Arabidopsis

The control of plant parasitic nematodes is an increasing problem. A key process during the infection is the induction of specialized nourishing cells, called giant cells (GCs), in roots. Understanding the function of genes required for GC development is crucial to identify targets for new control strategies. We propose a standardized method for GC phenotyping in different plant genotypes, like those with modified genes essential for GC development. The method combines images obtained by bright-field microscopy from the complete serial sectioning of galls with TrakEM2, specialized three-dimensional (3D) reconstruction software for biological structures. The volumes and shapes from 162 3D models of individual GCs induced by Meloidogyne javanica in Arabidopsis were analyzed for the first time along their life cycle. A high correlation between the combined volume of all GCs within a gall and the total area occupied by all the GCs in the section/s where they show maximum expansion, and a proof of concept from two Arabidopsis transgenic lines (J0121 ≫ DTA and J0121 ≫ GFP) demonstrate the reliability of the method. We phenotyped GCs and developed a reliable simplified method based on a two-dimensional (2D) parameter for comparison of GCs from different Arabidopsis genotypes, which is also applicable to galls from different plant species and in different growing conditions, as thickness/transparency is not a restriction.

Maturation of nematode-induced galls in Medicago truncatula is related to water status and primary metabolism modifications

Root-knot nematodes are obligatory plant parasitic worms that establish and maintain an intimate relationship with their host plants. During a compatible interaction, these nematodes induce the redifferentiation of root cells into multinucleate and hypertrophied giant cells (GCs). These metabolically active feeding cells constitute the exclusive source of nutrients for the nematode. We analyzed the modifications of water status, ionic content and accumulation of metabolites in development and mature galls induced by Meloidogyne incognita and in uninfected roots of Medicago truncatula plants. Water potential and osmotic pressure are significantly modified in mature galls compared to developing galls and control roots. Ionic content is significantly modified in galls compared to roots. Principal component analyses of metabolite content showed that mature gall metabolism is significantly modified compared to developing gall metabolism. The most striking differences were the three-fold increase of trehalose content associated to the five-fold diminution in glucose concentration in mature galls. Gene expression analysis showed that trehalose accumulation was, at least, partially linked to a significantly lower expression of the trehalase gene in mature galls. Our results point to significant modifications of gall physiology during maturation.

Comparative studies on the proteomic expression patterns in the third- and fifth-stage larvae of Angiostrongylus cantonensis

Angiostrongylus cantonensis is an important zoonotic parasite causing eosinophilic meningitis and eosinophilic meningoencephalitis in humans. In this study, the protein expression profiles of the infective third- and pathogenic fifth-stage larvae (L3 and L5) of this parasite were compared by proteomic techniques. Isolated protein samples were separated by two-dimensional gel electrophoresis (2-DE), stained with silver nitrate, and analyzed by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS). Proteins from L5 were mainly at pH 5-7 and with molecular weight (MW) 40-100 kDa, whereas those from L3 were at pH 5-6 and with 5-35 kDa. Of 100 protein spots identified, 33 were from L3 whereas 67 from L5 and 63 had known identities, whereas 37 were hypothetical proteins. There were 15 spots of stress proteins, and HSP60 was the most frequently found heat stress proteins in L5. More binding and protein transport-related proteins were found in L5 including peptidylprolyl isomerase (cyclophilin)-like 2, serum albumin, preproalbumin precursor, and dilute class unconventional myosin. L3 had a higher expression of cytoskeleton and membrane proteins than L5. In addition, four protein spots were identified in the sera of the rat host by Western blot analysis. The present proteomic study revealed different protein expression profiles in L3 and L5 of A. cantonensis. These changes may reflect the development of L3 from the poikilothermic snails to L5 in the homoeothemic rats. This information may be useful for the finding of stage-specific proteins and biomarker for diagnosis of angiostrongyliasis.

Nondestructive imaging of plant-parasitic nematode development and host response to nematode pathogenesis

The secluded lifestyle of endoparasitic plant nematodes hampers progress toward a comprehensive understanding of plant-nematode interactions. A novel technique that enables nondestructive, long-term observations of a wide range of live nematodes in planta is presented here. As proof of principle, Pratylenchus penetrans, Heterodera schachtii, and Meloidogyne chitwoodi were labeled fluorescently with PKH26 and used to infect Arabidopsis thaliana grown in microscopy rhizosphere chambers. Nematode behavior, development, and morphology were observed for the full duration of each parasite's life cycle by confocal microscopy for up to 27 days after inoculation. PKH26 accumulated in intestinal lipid droplets and had no negative effect on nematode infectivity. This technique enabled visualization of Meloidogyne gall formation, nematode oogenesis, and nematode morphological features, such as the metacorpus, vulva, spicules, and cuticle. Additionally, microscopy rhizosphere chambers were used to characterize plant organelle dynamics during M. chitwoodi infection. Peroxisome abundance strongly increased in early giant cells but showed a marked decrease at later stages of feeding site development, which suggests a modulation of plant peroxisomes by root-knot nematodes during the infection process. Taken together, this technique facilitates studies aimed at deciphering plant-nematode interactions at the cellular and subcellular level and enables unprecedented insights into nematode behavior in planta.

Nematode feeding sites: unique organs in plant roots

Although generally unnoticed, nearly all crop plants have one or more species of nematodes that feed on their roots, frequently causing tremendous yield losses. The group of sedentary nematodes, which are among the most damaging plant-parasitic nematodes, cause the formation of special organs called nematode feeding sites (NFS) in the root tissue. In this review we discuss key metabolic and cellular changes correlated with NFS development, and similarities and discrepancies between different types of NFS are highlighted.

Transcriptome profiling of the fifth-stage larvae of Angiostrongylus cantonensis by next-generation sequencing

Angiostrongylus cantonensis is an important zoonotic nematode. It is the causative agent of eosinophilic meningitis and eosinophilic meningoencephalitis in humans. However, information of this parasite at the genomic level is very limited. In the present study, the transcriptomic profiles of the fifth-stage larvae (L5) of A. cantonensis were investigated by next-generation sequencing (NGS). In the NGS database established from the larvae isolated from the brain of Sprague–Dawley rats, 31,487 unique genes with a mean length of 617 nucleotides were assembled. These genes were found to have a 46.08 % significant similarity to Caenorhabditis elegans by BLASTx. They were then compared with the expressed sequence tags of 18 other nematodes, and significant matches of 36.09–59.12 % were found. Among these genes, 3,338 were found to participate in 124 Kyoto Encyclopedia of Genes and Genomes pathways. These pathways included 1,514 metabolisms, 846 genetic information processing, 358 environmental information processing, 264 cellular processes, and 91 organismal systems. Analysis of 30,816 sequences with the gene ontology database indicated that their annotations included 5,656 biological processes (3,364 cellular processes, 3,061 developmental processes, and 3,191 multicellular organismal processes), 7,218 molecular functions (4,597 binding and 3,084 catalytic activities), and 4,719 cellular components (4,459 cell parts and 4,466 cells). Moreover, stress-related genes (112 heat stress and 33 oxidation stress) and genes for proteases (159) were not uncommon. This study is the first NGS-based study to set up a transcriptomic database of A. cantonensis L5. The results provide new insights into the survival, development, and host–parasite interactions of this blood-feeding nematode.

An immunocytochemical procedure for protein localization in various nematode life stages combined with plant tissues using methylacrylate-embedded specimens

Plant-parasitic nematodes possess a large number of proteins that are secreted in planta, allowing them to be successful parasites of plants. The majority of these proteins are synthesized mainly in the nematode subventral and dorsal glands as well as in other organs. To improve the immunovisualization of these proteins, we adapted a methacrylate embedding method for the localization of proteins inside nematode tissues, and extracellularly when secreted in planta or within plant cells. An important advantage is that the method is applicable for all nematode stages: preparasitic as well as parasitic stages, including large mature females. Herein, the method has been successfully applied for the localization of four nematode secreted proteins, such as Mi-MAP-1, Mi-CBM2-bearing proteins, Mi-PEL3, and Mi-6D4. In addition, we could also localize 14-3-3 proteins, as well as two cytoskeletal proteins, by double-immunolabeling on preparasitic juveniles. Superior preservation of nematode and plant morphology, allowed more accurate protein localization as compared with other methods. Besides excellent epitope preservation, dissolution of methacrylate from tissue sections unmasks target proteins and thereby drastically increases antibody access.

Whole-mount confocal imaging of nuclei in giant feeding cells induced by root-knot nematodes in Arabidopsis

• Excellent visualization of nuclei was obtained here using a whole-mount procedure adapted to provide high-resolution images of large, irregularly shaped nuclei. The procedure is based on tissue clearing, and fluorescent staining of nuclear DNA with the dye propidium iodide. • The method developed for standard confocal imaging was applied to large multicellular root swellings, named galls, induced in plant hosts by the root-knot nematode Meloidogyne incognita. • Here, we performed a functional analysis, and examined the nuclear structure in giant feeding cells overexpressing the cell cycle inhibitor Kip-related protein 4 (KRP4). Ectopic KRP4 expression in galls led to aberrant nuclear structure, disturbing giant cell expansion and nematode reproduction. In vivo live-cell imaging of GFP-KRP4 demonstrated that this protein co-localizes to chromosomes from prophase to late anaphase during cell cycle progression. • The data presented here suggest the involvement of KRP4 during mitotic progression in plant cells. The detailed results obtained using confocal analysis also demonstrate the potential utility of a rapid, easy-to-use clearing method for the analysis of the nuclei of certain Arabidopsis mutants and other complex plant nuclei.