The Mi-EFF1/Minc17998 effector interacts with the soybean GmHub6 protein to promote host plant parasitism by Meloidogyne incognita

Background: Meloidogyne incognita is the most frequently reported species from the root-knot nematode (RKN) complex responsible for causing damage in several different crops worldwide. The interaction between M. incognita and host plants involves the secretions of molecular factors from the nematode, which mainly suppress the defense response and promote plant parasitism. On the other hand, several plant elements are associated with the immune defense system that opposes nematode infection. Results: In this study, the interaction of the Mi-EFF1/Minc17998 effector with the soybean GmHub6 (Glyma.17G099100; TCP14) protein was identified and characterized in vivo and in planta. Data showed that the GmHub6 gene is upregulated by M. incognita infection in a nematode-resistant soybean cultivar (PI595099) compared to a susceptible cultivar (BRS133). Accordingly, the Arabidopsis thaliana AtHub6 mutant line (AT3G47620, orthologous gene of GmHub6 displayed normal vegetative development of the plant but was more susceptible to M. incognita. Thus, since the soybean and A. thaliana Hub6 proteins are TEOSINTE BRANCHED/CYCLOIDEA/PCF (TCP) transcription factors involved in plant development and morphogenesis modulation, flowering time regulation, and the activation of the plant immune system, our data suggest that the interaction of Mi-EFF1/Minc17998 and Hub6 proteins is associated with an increase in plant susceptibility to nematode infection during parasitism. It is suggested that this interaction may prevent the nuclear localization or disturb the activity of GmHub6 as a typical transcription factor modulating the cell cycle of the plant, avoid the activation of the host’s defense response, and successfully promote parasitism. Conclusion: Our findings indicate the potential of the Mi-EFF1/Minc17998 effector for the development of biotechnological tools based on the approaches of RNA interference and GmHub6 gene overexpression for RKN control.

Host-parasite tissue adhesion by a secreted type of β-1,4-glucanase in the parasitic plant Phtheirospermum japonicum

Tissue adhesion between plant species occurs both naturally and artificially. Parasitic plants establish intimate relationship with host plants by adhering tissues at roots or stems. Plant grafting, on the other hand, is a widely used technique in agriculture to adhere tissues of two stems. Here we found that the model Orobanchaceae parasitic plant Phtheirospermum japonicum can be grafted on to interfamily species. To understand molecular basis of tissue adhesion between distant plant species, we conducted comparative transcriptome analyses on both infection and grafting by P. japonicum on Arabidopsis. Despite different organs, we identified the shared gene expression profile, where cell proliferation- and cell wall modification-related genes are up-regulated. Among genes commonly induced in tissue adhesion between distant species, we showed a gene encoding a secreted type of β-1,4-glucanase plays an important role for plant parasitism. Our data provide insights into the molecular commonality between parasitism and grafting in plants.

The Mi-EFF1/Minc17998 effector interacts with the soybean GmHub6 protein to promote host plant parasitism by Meloidogyne incognita

Background: Meloidogyne incognita is the most frequently reported species from the root-knot nematode (RKN) complex responsible for causing damage in several different crops worldwide. The interaction between M. incognita and host plants involves the secretions of molecular factors from the nematode, which mainly suppress the defense response and promote plant parasitism. On the other hand, several plant elements are associated with the immune defense system that opposes nematode infection.Results: In this study, the interaction of the Mi-EFF1/Minc17998 effector with the soybean GmHub6 (Glyma.17G099100; TCP14) protein was identified and characterized in vitro and in vivo. Data showed that the GmHub6 gene is upregulated by M. incognita infection in a nematode-resistant soybean cultivar (PI595099) compared to a susceptible cultivar (BRS133). Accordingly, the Arabidopsis thaliana AtHub6 mutant line (AT3G47620, orthologous gene of GmHub6 displayed normal vegetative development of the plant but was more susceptible to M. incognita. Thus, since the soybean and A. thaliana Hub6 proteins are TEOSINTE BRANCHED/CYCLOIDEA/PCF (TCP) transcription factors involved in plant development and morphogenesis modulation, flowering time regulation, and the activation of the plant immune system, our data suggest that the interaction of Mi-EFF1/Minc17998 and Hub6 proteins is associated with an increase in plant susceptibility to nematode infection during parasitism. It is suggested that this interaction may prevent the nuclear localization or disturb the activity of GmHub6 as a typical transcription factor modulating the cell cycle of the plant, avoid the activation of the host’s defense response, and successfully promote parasitism.Conclusion: Our findings indicate the potential of the Mi-EFF1/Minc17998 effector for the development of biotechnological tools based on the approaches of RNA interference and GmHub6 gene overexpression for RKN control.

Comparative Ergot Alkaloid Elaboration by Selected Plectenchymatic Mycelia of Claviceps purpurea through Sequential Cycles of Axenic Culture and Plant Parasitism

Ergot alkaloids have an established place in plant pathology and toxicology. As pharmaceuticals, their sourcing is via natural or managed agricultural occurrence of sclerotia of Claviceps purpurea (Fr.) Tul. or through industrial fermentation processes with other Claviceps. The key factor for biosynthesis is differentiation of a particular mycelial anatomy. Previous study of these fungi from two disparate English grass genera, Spartina and Phragmites, has shown that only mycelia expressing a plectenchymatic sclerotium-like anatomy in specific axenic culture conditions elaborated ergot alkaloids, and then only as far as lysergic acid. The present report describes sequential cycles of axenic and parasitic cultivation for wild isolates from Dactylis and Alopecurus with intervention of a single ascospore step. This confirms the homozygous character of C. purpurea and defines several potential experimental axenic and parasitic conditions within the species for comparing genomic aspects of partial or full biosynthesis of cyclic tri-peptide alkaloids. Whereas Alopecurus ergot isolates readily parasitized rye, use of Dactylis isolates as inoculum for rye ovaries failed to cause the usual sphacelial fructification but supported growth of exceptionally thin sclerotia, sometimes two in a floret, with low alkaloid content attributed to reduced medullary component. However, after two cycles of axenic and rye-parasitic cultivation, and consistent re-selection of the plectenchymatic character in axenic mycelia, typical growth of ergot sclerotia occurred on rye. Caution thus seems necessary in tests for putative host specificity in any taxonomic realignments within the classical concept of C. purpurea. A Dactylis ergot isolate was also uniquely shown to parasitise the plumule of germinating rye seeds confirming the susceptibility of apical tissues. A key biosynthetic feature of a mycelial glyceride oil, rich in ricinoleic acid, as a prelude to axenic and parasitic formation of ergot alkaloids by C. purpurea is emphasised.

Molecular Dialog Between Parasitic Plants and Their Hosts

Parasitic plants steal sugars, water, and other nutrients from host plants through a haustorial connection. Several species of parasitic plants such as witchweeds ( Striga spp.) and broomrapes ( Orobanche and Phelipanche spp.) are major biotic constraints to agricultural production. Parasitic plants are understudied compared with other major classes of plant pathogens, but the recent availability of genomic and transcriptomic data has accelerated the rate of discovery of the molecular mechanisms underpinning plant parasitism. Here, we review the current body of knowledge of how parasitic plants sense host plants, germinate, form parasitic haustorial connections, and suppress host plant immune responses. Additionally, we assess whether parasitic plants fit within the current paradigms used to understand the molecular mechanisms of microbial plant–pathogen interactions. Finally, we discuss challenges facing parasitic plant research and propose the most urgent questions that need to be answered to advance our understanding of plant parasitism.

Differential feeding site development and reproductive fitness of Meloidogyne incognita and M. javanica on zucchini, a source of resistance to M. incognita

The development of Meloidogyne incognita and M. javanica on zucchini ‘Amalthee’ was compared to characterise critical events in plant parasitism. Meloidogyne incognita was much less successful parasitising zucchini than M. javanica despite similarities in penetration rates and juvenile development. The increased frequency of undersized individuals, immature females and empty galls evidenced a failure in M. incognita development. Meloidogyne incognita induced larger feeding sites that contained more and larger giant cells than did M. javanica. Malformation of the M. incognita giant cells and abnormal growth of the surrounding tissues was observed at both 11 and 25 days post-inoculation. Critical events in parasitism differentiating the nematode isolates were the transition from fourth-stage juveniles to females, and the reduced fertility of the egg-laying females. Zucchini can be considered a source of resistance to M. incognita because it restricted nematode proliferation by supporting less fertile egg-laying females and producing fewer egg masses and total eggs.

Terrestrial invertebrates in the Rhynie chert ecosystem

The Early Devonian Rhynie and Windyfield cherts remain a key locality for understanding early life and ecology on land. They host the oldest unequivocal nematode worm (Nematoda), which may also offer the earliest evidence for herbivory via plant parasitism. The trigonotarbids (Arachnida: Trigonotarbida) preserve the oldest book lungs and were probably predators that practiced liquid feeding. The oldest mites (Arachnida: Acariformes) are represented by taxa which include mycophages and predators on nematodes today. The earliest harvestman (Arachnida: Opiliones) includes the first preserved tracheae, and male and female genitalia. Myriapods are represented by a scutigeromorph centipede (Chilopoda: Scutigeromorpha), probably a cursorial predator on the substrate, and a putative millipede (Diplopoda). The oldest springtails (Hexapoda: Collembola) were probably mycophages, and another hexapod of uncertain affinities preserves a gut infill of phytodebris. The first true insects (Hexapoda: Insecta) are represented by a species known from chewing (non-carnivorous?) mandibles. Coprolites also provide insights into diet, and we challenge previous assumptions that several taxa were spore-feeders. Rhynie appears to preserve a largely intact community of terrestrial animals, although some expected groups are absent. The known fossils are (ecologically) consistent with at least part of the fauna found around modern Icelandic hot springs. This article is part of a discussion meeting issue ‘The Rhynie cherts: our earliest terrestrial ecosystem revisited’.