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

Allium cepa tests: Exploring bleomycin induced cyto-genotoxicity and altered cell cycle kinetics in root tips meristematic cells

Bleomycin, commonly employed in treating Hodgkin's lymphoma and testicular cancer, is associated with significant pulmonary toxicity. While various studies have assessed the toxic impact of chemotherapeutic agents on aquatic and terrestrial environments, limited data exist on bleomycin's effects, especially concerning higher plants. To address this gap, we utilized the Allium cepa assays, renowned for evaluating chemical and biochemical agents' toxic effects, to investigate bleomycin's impact on the terrestrial ecosystem. Our study aimed to assess bleomycin's cyto-genotoxic effects on A. cepa root tip cells at minimal concentrations (10-40 μg mL-1) and varied exposure durations (2, 4, 6, and 24 h). Analysis of nuclear and mitotic abnormalities in bleomycin-treated A. cepa root tip cells, alongside an acridine orange-ethidium bromide double staining assay, illuminated its influence on cell viability. Additionally, agarose gel electrophoresis determined the drug's potential for DNA degradation, unveiling the underlying mechanisms of cyto-genotoxicity. Results also demonstrated a decline in the mitotic index with increased bleomycin concentrations and exposure time, elevated frequencies of various cyto-genotoxic abnormalities, including sticky chromosomes, chromatid breaks, laggards, bridges, polar deviations, nuclear lesions, and hyperchromasia. The study indicated the potential risks of bleomycin even at low concentrations and brief exposures, highlighting its severe adverse effects on genetic material of plant, potentially contributing to cell death. Consequently, this investigation unveils bleomycin's cyto-genotoxic effects on higher plant system, underscoring its threat to terrestrial ecosystems, particularly upon chronic and unmonitored exposure.

Giant cells: multiple cells unite to survive

Multinucleated Giant Cells (MGCs) are specialized cells that develop from the fusion of multiple cells, and their presence is commonly observed in human cells during various infections. However, MGC formation is not restricted to infections alone but can also occur through different mechanisms, such as endoreplication and abortive cell cycle. These processes lead to the formation of polyploid cells, eventually resulting in the formation of MGCs. In Entamoeba, a protozoan parasite that causes amoebic dysentery and liver abscesses in humans, the formation of MGCs is a unique phenomenon and not been reported in any other protozoa. This organism is exposed to various hostile environmental conditions, including changes in temperature, pH, and nutrient availability, which can lead to stress and damage to its cells. The formation of MGCs in Entamoeba is thought to be a survival strategy to cope with these adverse conditions. This organism forms MGCs through cell aggregation and fusion in response to osmotic and heat stress. The MGCs in Entamoeba are thought to have increased resistance to various stresses and can survive longer than normal cells under adverse conditions. This increased survival could be due to the presence of multiple nuclei, which could provide redundancy in case of DNA damage or mutations. Additionally, MGCs may play a role in the virulence of Entamoeba as they are found in the inflammatory foci of amoebic liver abscesses and other infections caused by Entamoeba. The presence of MGCs in these infections suggests that they may contribute to the pathogenesis of the disease. Overall, this article offers valuable insights into the intriguing phenomenon of MGC formation in Entamoeba. By unraveling the mechanisms behind this process and examining its implications, researchers can gain a deeper understanding of the complex biology of Entamoeba and potentially identify new targets for therapeutic interventions. The study of MGCs in Entamoeba serves as a gateway to exploring the broader field of cell fusion in various organisms, providing a foundation for future investigations into related cellular processes and their significance in health and disease.

The DNA methylation landscape of the root-knot nematode-induced pseudo-organ, the gall, in Arabidopsis, is dynamic, contrasting over time, and critically important for successful parasitism

Root-knot nematodes (RKNs) induce giant cells (GCs) within galls which are characterized by large-scale gene repression at early stages. However, the epigenetic mechanism(s) underlying gene silencing is (are) still poorly characterized. DNA methylation in Arabidopsis galls induced by Meloidogyne javanica was studied at crucial infection stages (3 d post-infection (dpi) and 14 dpi) using enzymatic, cytological, and sequencing approaches. DNA methyltransferase mutants (met1, cmt2, cmt3, cmt2/3, drm1/2, ddc) and a DNA demethylase mutant (ros1), were analyzed for RKN resistance/tolerance, and galls were characterized by confocal microscopy and RNA-seq. Early galls were hypermethylated, and the GCs were found to be the major contributors to this hypermethylation, consistent with the very high degree of gene repression they exhibit. By contrast, medium/late galls showed no global increase in DNA methylation compared to uninfected roots, but exhibited large-scale redistribution of differentially methylated regions (DMRs). In line with these findings, it was also shown that DNA methylation and demethylation mutants showed impaired nematode reproduction and gall/GC-development. Moreover, siRNAs that were exclusively present in early galls accumulated at hypermethylated DMRs, overlapping mostly with retrotransposons in the CHG/CG contexts that might be involved in their repression, contributing to their stability/genome integrity. Promoter/gene methylation correlated with differentially expressed genes encoding proteins with basic cell functions. Both mechanisms are consistent with reprogramming host tissues for gall/GC formation. In conclusion, RNA-directed DNA methylation (RdDM; DRM2/1) pathways, maintenance methyltransferases (MET1/CMT3) and demethylation (ROS1) appear to be prominent mechanisms driving a dynamic regulation of the epigenetic landscape during RKN infection.

Overexpression of a soybean Globin (GmGlb1-1) gene reduces plant susceptibility to Meloidogyne incognita

The overexpression of the GmGlb1-1 gene reduces plant susceptibility to Meloidogyne incognita. Non-symbiotic globin class #1 (Glb1) genes are expressed in different plant organs, have a high affinity for oxygen, and are related to nitric oxide (NO) turnover. Previous studies showed that soybean Glb1 genes are upregulated in soybean plants under flooding conditions. Herein, the GmGlb1-1 gene was identified in soybean as being upregulated in the nematode-resistant genotype PI595099 compared to the nematode-susceptible cultivar BRS133 during plant parasitism by Meloidogyne incognita. The Arabidopsis thaliana and Nicotiana tabacum transgenic lines overexpressing the GmGlb1-1 gene showed reduced susceptibility to M. incognita. Consistently, gall morphology data indicated that pJ2 nematodes that infected the transgenic lines showed developmental alterations and delayed parasitism progress. Although no significant changes in biomass and seed yield were detected, the transgenic lines showed an elongated, etiolation-like growth under well-irrigation, and also developed more axillary roots under flooding conditions. In addition, transgenic lines showed upregulation of some important genes involved in plant defense response to oxidative stress. In agreement, higher hydrogen peroxide accumulation and reduced activity of reactive oxygen species (ROS) detoxification enzymes were also observed in these transgenic lines. Thus, based on our data and previous studies, it was hypothesized that constitutive overexpression of the GmGlb1-1 gene can interfere in the dynamics of ROS production and NO scavenging, enhancing the acquired systemic acclimation to biotic and abiotic stresses, and improving the cellular homeostasis. Therefore, these collective data suggest that ectopic or nematode-induced overexpression, or enhanced expression of the GmGlb1-1 gene using CRISPR/dCas9 offers great potential for application in commercial soybean cultivars aiming to reduce plant susceptibility to M. incognita.

The Minichromosome Maintenance Complex Component 2 (MjMCM2) of Meloidogyne javanica is a potential effector regulating the cell cycle in nematode-induced galls

Root-knot nematodes Meloidogyne spp. induce enlarged multinucleate feeding cells—galls—in host plant roots. Although core cell-cycle components in galls follow a conserved track, they can also be usurped and manipulated by nematodes. We identified a candidate effector in Meloidogyne javanica that is directly involved in cell-cycle manipulation—Minichromosome Maintenance Complex Component 2 (MCM2), part of MCM complex licensing factor involved in DNA replication. MjMCM2, which is induced by plant oxilipin 9-HOT, was expressed in nematode esophageal glands, upregulated during parasitic stages, and was localized to plant cell nucleus and plasma membrane. Infected tomato hairy roots overexpressing MjMCM2 showed significantly more galls and egg-mass-producing females than wild-type roots, and feeding cells showed more nuclei. Phylogenetic analysis suggested seven homologues of MjMCM2 with unknown association to parasitism. Sequence mining revealed two RxLR-like motifs followed by SEED domains in all Meloidogyne spp. MCM2 protein sequences. The unique second RxLR-like motif was absent in other Tylenchida species. Molecular homology modeling of MjMCM2 suggested that second RxLR2-like domain is positioned on a surface loop structure, supporting its function in polar interactions. Our findings reveal a first candidate cell-cycle gene effector in M. javanica—MjMCM2—that is likely secreted into plant host to mimic function of endogenous MCM2.

Rhizobial infection of 4C cells triggers their endoreduplication during symbiotic nodule development in soybean

Symbiosis between legumes and rhizobia results in the formation of nitrogen-fixing root nodules. Endoreduplication is essential for nodule development and efficient nitrogen fixation; however, the cellular mechanism by which rhizobial infection causes endoreduplication in symbiotic nodules and the roles of the resulting polyploid cells in nitrogen fixation remain largely unknown. Here, we developed a series of different approaches to separate infected cells (ICs) and uninfected cells (UCs) and determined their ploidy levels in soybean (Glycine max) developing nodules. We demonstrated that 4C nuclei exist in both UCs and ICs of developing nodules and that these 4C cells are primarily invaded by rhizobia and subsequently undergo endoreduplication. Furthermore, RNA-sequencing analysis of nuclei with different ploidy levels from soybean nodules at 12 d post-infection (dpi) and 20 dpi showed that 4C cells are predominantly ICs in 12-dpi nodules but UCs in 20-dpi nodules. We conclude that the infection of 4C cells by rhizobia is critical for initiating endoreduplication. These findings provide significant insight into rhizobial infection, nodule endoreduplication and nitrogen fixation in symbiotic nodules.

Development of Microscopic Techniques for the Visualization of Plant–Root-Knot Nematode Interaction

Plant-parasitic nematodes are a significant cause of yield losses and food security issues. Specifically, nematodes of the genus Meloidogyne can cause significant production losses in horticultural crops around the world. Understanding the mechanisms of the ever-changing physiology of plant roots by imaging the galls induced by nematodes could provide a great insight into their control. However, infected roots are unsuitable for light microscopy investigation due to the opacity of plant tissues. Thus, samples must be cleared to visualize the interior of whole plants in order to make them transparent using clearing agents. This work aims to identify which clearing protocol and microscopy system is the most appropriate to obtain 3D images of tomato cv. Durinta and eggplant cv. Cristal samples infected with Meloidogyne incognita to visualize and study the root–nematode interaction. To that extent, two clearing solutions (BABB and ECi), combined with three different dehydration solvents (ethanol, methanol and 1-propanol), are tested. In addition, the advantages and disadvantages of alternative imaging techniques to confocal microscopy are analyzed by employing an experimental custom-made setup that combines two microscopic techniques, light sheet fluorescence microscopy and optical projection tomography, on a single instrument.

Pulsatility Index in the Basal Ganglia Arteries Increases with Age in Elderly with and without Cerebral Small Vessel Disease

BACKGROUND AND PURPOSE

Cerebral small vessel disease contributes to stroke and cognitive impairment and interacts with Alzheimer disease pathology. Because of the small dimensions of the affected vessels, in vivo characterization of blood flow properties is challenging but important to unravel the underlying mechanisms of the disease.

MATERIALS AND METHODS

A 2D phase-contrast sequence at 7T MR imaging was used to assess blood flow velocity and the pulsatility index of the perforating basal ganglia arteries. We included patients with cerebral amyloid angiopathy (n = 8; identified through the modified Boston criteria), hypertensive arteriopathy (n = 12; identified through the presence of strictly deep or mixed cerebral microbleeds), and age- and sex-matched controls (n = 28; no cerebral microbleeds).

RESULTS

Older age was related to a greater pulsatility index, irrespective of cerebral small vessel disease. In hypertensive arteriopathy, there was an association between lower blood flow velocity of the basal ganglia and the presence of peri-basal ganglia WM hyperintensities.

CONCLUSIONS

Our results suggest that age might be the driving factor for altered cerebral small vessel hemodynamics. Furthermore, this study puts cerebral small vessel disease downstream pathologies in the basal ganglia region in relation to blood flow characteristics of the basal ganglia microvasculature.

Minc00344 and Mj-NULG1a effectors interact with GmHub10 protein to promote the soybean parasitism by Meloidogyne incognita and M. javanica

Several economically important crops are susceptible to root-knot nematode (RKNs). Meloidogyne incognita and M. javanica are the two most reported species from the RKN complex, causing damage to several crops worldwide. The successful outcome of the Meloidogyne-plant interaction is associated with molecular factors secreted by the nematode to suppress the plant's immune response and promote nematode parasitism. In contrast, several plant factors are associated with defense against nematode infection. In this study, we identified and characterized the specific interaction of Minc00344 and Mj-NULG1a effectors with soybean GmHub10 (Glyma.19G008200) protein in vitro and in vivo. An Arabidopsis thaliana T-DNA mutant of AtHub10 (AT3G27960, an orthologous gene of GmHub10) showed higher susceptibility to M. incognita. Thus, since soybean and A. thaliana Hub10 proteins are involved in pollen tube growth and indirect activation of the defense response, our data suggest that effector-Hub10 interactions could be associated with an increase in plant susceptibility. These findings indicate the potential of these effector proteins to develop new biotechnological tools based on RNA interference and the overexpression of engineered Hub10 proteins for the efficient management of RKN in crops.

Giant cells: Linking McClintock's heredity to early embryogenesis and tumor origin throughout millennia of evolution on Earth

The "life code" theory postulates that egg cells, which are giant, are the first cells in reproduction and that damaged or aged giant somatic cells are the first cells in tumorigenesis. However, the hereditary basis for giant cells remains undefined. Here I propose that stress-induced genomic reorganization proposed by Nobel Laureate Barbara McClintock may represent the underlying heredity for giant cells, referred to as McClintock's heredity. Increase in cell size may serve as a response to environmental stress via switching proliferative mitosis to intranuclear replication for reproduction. Intranuclear replication activates McClintock's heredity to reset the genome following fertilization for reproduction or restructures the somatic genome for neoplastic transformation via formation of polyploid giant cancer cells (PGCCs). The genome-based McClintock heredity functions together with gene-based Mendel's heredity to regulate the genomic stability at two different stages of life cycle or tumorigenesis. Thus, giant cells link McClintock's heredity to both early embryogenesis and tumor origin. Cycling change in cell size together with ploidy number switch may represent the most fundamental mechanism on how both germ and soma for coping with environmental stresses for the survival across the tree of life which evolved over millions of years on Earth.

The Armadillo BTB Protein ABAP1 Is a Crucial Player in DNA Replication and Transcription of Nematode-Induced Galls

The biogenesis of root-knot nematode (Meloidogyne spp.)-induced galls requires the hyperactivation of the cell cycle with controlled balance of mitotic and endocycle programs to keep its homeostasis. To better understand gall functioning and to develop new control strategies for this pest, it is essential to find out how the plant host cell cycle programs are responding and integrated during the nematode-induced gall formation. This work investigated the spatial localization of a number of gene transcripts involved in the pre-replication complex during DNA replication in galls and report their akin colocation with the cell cycle S-phase regulator Armadillo BTB Arabidopsis Protein 1 (ABAP1). ABAP1 is a negative regulator of pre-replication complex controlling DNA replication of genes involved in control of cell division and proliferation; therefore, its function has been investigated during gall ontogenesis. Functional analysis was performed upon ABAP1 knockdown and overexpression in Arabidopsis thaliana. We detected ABAP1 promoter activity and localized ABAP1 protein in galls during development, and its overexpression displayed significantly reduced gall sizes containing atypical giant cells. Profuse ABAP1 expression also impaired gall induction and hindered nematode reproduction. Remarkably, ABAP1 knockdown likewise negatively affected gall and nematode development, suggesting its involvement in the feeding site homeostasis. Microscopy analysis of cleared and nuclei-stained whole galls revealed that ABAP1 accumulation resulted in aberrant giant cells displaying interconnected nuclei filled with enlarged heterochromatic regions. Also, imbalanced ABAP1 expression caused changes in expression patterns of genes involved in the cell division control as demonstrated by qRT-PCR. CDT1a, CDT1b, CDKA;1, and CYCB1;1 mRNA levels were significantly increased in galls upon ABAP1 overexpression, possibly contributing to the structural changes in galls during nematode infection. Overall, data obtained in galls reinforced the role of ABAP1 controlling DNA replication and mitosis and, consequently, cell proliferation. ABAP1 expression might likely take part of a highly ordered mechanism balancing of cell cycle control to prevent gall expansion. ABAP1 expression might prevent galls to further expand, limiting excessive mitotic activity. Our data strongly suggest that ABAP1 as a unique plant gene is an essential component for cell cycle regulation throughout gall development during nematode infection and is required for feeding site homeostasis.

Infection by cyst nematodes induces rapid remodelling of developing xylem vessels in wheat roots

Cyst nematodes induce host-plant root cells to form syncytia from which the nematodes feed. Comprehensive histological investigation of these feeding sites is complicated by their variable shape and their positions deep within root tissue. Using tissue clearing and confocal microscopy, we examined thick (up to 150 μm) sections of wheat roots infected by cereal cyst nematodes (Heterodera avenae). This approach provided clear views of feeding sites and surrounding tissues, with resolution sufficient to reveal spatial relationships among nematodes, syncytia and host vascular tissues at the cellular level. Regions of metaxylem vessels near syncytia were found to have deviated from classical developmental patterns. Xylem vessel elements in these regions had failed to elongate but had undergone radial expansion, becoming short and plump rather than long and cylindrical. Further investigation revealed that vessel elements cease to elongate shortly after infection and that they later experience delays in secondary thickening (lignification) of their outer cell walls. Some of these elements were eventually incorporated into syncytial feeding sites. By interfering with a developmental program that normally leads to programmed cell death, H. avenae may permit xylem vessel elements to remain alive for later exploitation by the parasite.

MiDaf16-like and MiSkn1-like gene families are reliable targets to develop biotechnological tools for the control and management of Meloidogyne incognita

Meloidogyne incognita is a plant-parasitic root-knot nematode (RKN, PPN) responsible for causing damage to several crops worldwide. In Caenorhabditis elegans, the DAF-16 and SKN-1 transcription factors (TFs) orchestrate aging, longevity, and defense responses to several stresses. Here, we report that MiDaf16-like1 and MiSkn1-like1, which are orthologous to DAF-16 and SKN-1 in C. elegans, and some of their targets, are modulated in M. incognita J2 during oxidative stress or plant parasitism. We used RNAi technology for the stable production of siRNAs in planta to downregulate the MiDaf16-like1 and MiSkn1-like1 genes of M. incognita during host plant parasitism. Arabidopsis thaliana and Nicotiana tabacum overexpressing a hairpin-derived dsRNA targeting these genes individually (single-gene silencing) or simultaneously (double-gene silencing) were generated. T2 plants were challenged with M. incognita and the number of eggs, galls, and J2, and the nematode reproduction factor (NRF) were evaluated. Our data indicate that MiDaf16-like1, MiSkn1-like1 and some genes from their networks are modulated in M. incognita J2 during oxidative stress or plant parasitism. Transgenic A. thaliana and N. tabacum plants with single- or double-gene silencing showed significant reductions in the numbers of eggs, J2, and galls, and in NRF. Additionally, the double-gene silencing plants had the highest resistance level. Gene expression assays confirmed the downregulation of the MiDaf16-like1 and MiSkn1-like1 TFs and defense genes in their networks during nematode parasitism in the transgenic plants. All these findings demonstrate that these two TFs are potential targets for the development of biotechnological tools for nematode control and management in economically important crops.

The plant WEE1 kinase is involved in checkpoint control activation in nematode-induced galls

Galls induced by plant-parasitic nematodes involve a hyperactivation of the plant mitotic and endocycle machinery for their profit. Dedifferentiation of host root cells includes drastic cellular and molecular readjustments. In such a background, potential DNA damage in the genome of gall cells is evident. We investigated whether DNA damage checkpoint activation followed by DNA repair occurred, or was eventually circumvented, in nematode-induced galls. Galls display transcriptional activation of the DNA damage checkpoint kinase WEE1, correlated with its protein localization in the nuclei. The promoter of the stress marker gene SMR7 was evaluated under the WEE1-knockout background. Drugs inducing DNA damage and a marker for DNA repair, PARP1, were used to understand the mechanisms for coping with DNA damage in galls. Our functional study revealed that gall cells lacking WEE1 conceivably entered mitosis prematurely, disturbing the cell cycle despite the loss of genome integrity. The disrupted nuclei phenotype in giant cells hinted at the accumulation of mitotic defects. In addition, WEE1-knockout in Arabidopsis and downregulation in tomato repressed infection and reproduction of root-knot nematodes. Together with data on DNA-damaging drugs, we suggest a conserved function for WEE1 in controlling G1/S cell cycle arrest in response to a replication defect in galls.

Size matters: three methods for estimating nuclear size in mycorrhizal roots of Medicago truncatula by image analysis

BACKGROUND

The intracellular accommodation of arbuscular mycorrhizal (AM) fungi involves a profound molecular reprogramming of the host cell architecture and metabolism, based on the activation of a symbiotic signaling pathway. In analogy with other plant biotrophs, AM fungi are reported to trigger cell cycle reactivation in their host tissues, possibly in support of the enhanced metabolic demand required for the symbiosis.

RESULTS

We here compare the efficiency of three Fiji/ImageJ image analysis plugins in localizing and quantifying the increase in nuclear size - a hallmark of recursive events of endoreduplication - in M. truncatula roots colonized by the AM fungus Gigaspora margarita. All three approaches proved to be versatile and upgradeable, allowing the investigation of nuclear changes in a complex tissue; 3D Object Counter provided more detailed information than both TrackMate and Round Surface Detector plugins. On this base we challenged 3D Object Counter with two case studies: verifying the lack of endoreduplication-triggering responses in Medicago truncatula mutants with a known non-symbiotic phenotype; and analysing the correlation in space and time between the induction of cortical cell division and endoreduplication upon AM colonization. Both case studies revealed important biological aspects. Mutant phenotype analyses have demonstrated that the knock-out mutation of different key genes in the symbiotic signaling pathway block AM-associated endoreduplication. Furthermore, our data show that cell divisions occur during initial stages of root colonization and are followed by recursive activation of the endocycle in preparation for arbuscule accommodation.

CONCLUSIONS

In conclusion, our results indicate 3D Object Counter as the best performing Fiji/ImageJ image analysis script in plant root thick sections and its application highlighted endoreduplication as a major feature of the AM pre-penetration response in root cortical cells.

Size matters: three methods for estimating nuclear size in mycorrhizal roots of Medicago truncatula by image analysis

BACKGROUND

The intracellular accommodation of arbuscular mycorrhizal (AM) fungi involves a profound molecular reprogramming of the host cell architecture and metabolism, based on the activation of a symbiotic signaling pathway. In analogy with other plant biotrophs, AM fungi are reported to trigger cell cycle reactivation in their host tissues, possibly in support of the enhanced metabolic demand required for the symbiosis.

RESULTS

We here compare the efficiency of three Fiji/ImageJ image analysis plugins in localizing and quantifying the increase in nuclear size - a hallmark of recursive events of endoreduplication - in M. truncatula roots colonized by the AM fungus Gigaspora margarita. All three approaches proved to be versatile and upgradeable, allowing the investigation of nuclear changes in a complex tissue; 3D Object Counter provided more detailed information than both TrackMate and Round Surface Detector plugins. On this base we challenged 3D Object Counter with two case studies: verifying the lack of endoreduplication-triggering responses in Medicago truncatula mutants with a known non-symbiotic phenotype; and analysing the correlation in space and time between the induction of cortical cell division and endoreduplication upon AM colonization. Both case studies revealed important biological aspects. Mutant phenotype analyses have demonstrated that the knock-out mutation of different key genes in the symbiotic signaling pathway block AM-associated endoreduplication. Furthermore, our data show that cell divisions occur during initial stages of root colonization and are followed by recursive activation of the endocycle in preparation for arbuscule accommodation.

CONCLUSIONS

In conclusion, our results indicate 3D Object Counter as the best performing Fiji/ImageJ image analysis script in plant root thick sections and its application highlighted endoreduplication as a major feature of the AM pre-penetration response in root cortical cells.

A Phenotyping Method of Giant Cells from Root-Knot Nematode Feeding Sites by Confocal Microscopy Highlights a Role for CHITINASE-LIKE 1 in Arabidopsis

Most effective nematicides for the control of root-knot nematodes are banned, which demands a better understanding of the plant-nematode interaction. Understanding how gene expression in the nematode-feeding sites relates to morphological features may assist a better characterization of the interaction. However, nematode-induced galls resulting from cell-proliferation and hypertrophy hinders such observation, which would require tissue sectioning or clearing. We demonstrate that a method based on the green auto-fluorescence produced by glutaraldehyde and the tissue-clearing properties of benzyl-alcohol/benzyl-benzoate preserves the structure of the nematode-feeding sites and the plant-nematode interface with unprecedented resolution quality. This allowed us to obtain detailed measurements of the giant cells’ area in an Arabidopsis line overexpressing CHITINASE-LIKE-1 (CTL1) from optical sections by confocal microscopy, assigning a role for CTL1 and adding essential data to the scarce information of the role of gene repression in giant cells. Furthermore, subcellular structures and features of the nematodes body and tissues from thick organs formed after different biotic interactions, i.e., galls, syncytia, and nodules, were clearly distinguished without embedding or sectioning in different plant species (Arabidopsis, cucumber or Medicago). The combination of this method with molecular studies will be valuable for a better understanding of the plant-biotic interactions.

Plant Cyclin-Dependent Kinase Inhibitors of the KRP Family: Potent Inhibitors of Root-Knot Nematode Feeding Sites in Plant Roots

Root-knot nematodes (RKN), Meloidogyne spp., are distributed worldwide and impose severe economic damage to many agronomically important crops. The plant cell cycle machinery is considered one of the pivotal components for the formation of nematode feeding sites (NFSs) or galls. These feeding sites contain five to nine hypertrophied giant cells (GC) resulting from developmental reprogramming of host root cells by this pathogen. GC undergo synchronous waves of mitotic activity uncoupled from cytokinesis giving rise to large multinucleate cells. As development of the NFS progresses, multiple rounds of DNA synthesis occur in the nuclei of GC, coupled with nuclear and cellular expansion. These cells are highly metabolically active and provide the nematode with nutrients necessary for its development and completion of its life cycle. In Arabidopsis seven cyclin dependent kinase inhibitors (CKIs) belonging to the interactors/inhibitors of the cyclin dependent kinases (ICK) family, also referred as Kip-Related Proteins (KRPs) have been identified. Interactions of KRPs with CDK/Cyclin complexes decrease CDK activity, affecting both cell cycle progression and DNA content in a concentration-dependent manner. We performed the functional analysis of all Arabidopsis KRP gene members during RKN interaction in Arabidopsis to obtain more insight into their role during gall development. We demonstrated that three members of this family (KRP2, KRP5, and KRP6) were highly expressed in galls and were important for cell cycle regulation during NFS development as shown by their different modes of action. We also pointed out that cell cycle inhibition through overexpression of all members of the KRP family can affect NFS development and consequently compromise the nematode's life cycle. In this review we summarized our recent understanding of the KRP family of genes, and their role in controlling cell cycle progression at the RKN feeding site.