Induces Gall Formation Research Articles

Comparative transcriptome reprogramming in oak galls containing asexual or sexual generations of gall wasps.

Oak gall wasps have evolved strategies to manipulate the developmental pathways of their host to induce gall formation. This provides shelter and nutrients for the developing larva. Galls are entirely host tissue; however, the initiation, development, and physical appearance are controlled by the inducer. The underlying molecular mechanisms of gall formation, by which one or a small number of cells are reprogrammed and commit to a novel developmental path, are poorly understood. In this study, we sought a deeper insight into the molecular underpinnings of this process. Oak gall wasps have two generations each year, one sexual, and one asexual. Galls formed by these two generations exhibit a markedly different appearance. We sequenced transcriptomes of both the asexual and sexual generations of Neuroterus quercusbaccarum and Neuroterus numismalis. We then deployed Nanopore sequencing to generate long-read sequences to test the hypothesis that gall wasps introduce DNA insertions to determine gall development. We detected potential genome rearrangements but did not uncover any non-host DNA insertions. Transcriptome analysis revealed that transcriptomes of the sexual generations of distinct species of wasp are more similar than inter-generational comparisons from the same species of wasp. Our results highlight the intricate interplay between the host leaves and gall development, suggesting that season and requirements of the gall structure play a larger role than species in controlling gall development and structure.

Identification of a novel viral factor inducing tumorous symptoms by disturbing vascular development in planta.

Plant viruses induce various disease symptoms that substantially impact agriculture, but the underlying mechanisms of viral disease in plants are poorly understood. Kobu-sho is a disease in gentian that shows gall formation with ectopic development of lignified cells and vascular tissues such as xylem. Here, we show that a gene fragment of gentian Kobu-sho-associated virus, which is designated as Kobu-sho-inducing factor (KOBU), induces gall formation accompanied by ectopic development of lignified cells and xylem-like tissue in Nicotiana benthamiana. Transgenic gentian expressing KOBU exhibited tumorous symptoms, confirming the gall-forming activity of KOBU. Surprisingly, KOBU expression can also induce differentiation of an additional leaf-like tissue on the abaxial side of veins in normal N. benthamiana and gentian leaves. Transcriptome analysis with Arabidopsis thaliana expressing KOBU revealed that KOBU activates signaling pathways that regulate xylem development. KOBU protein forms granules and plate-like structures and co-localizes with mRNA splicing factors within the nucleus. Our findings suggest that KOBU is a novel pleiotropic virulence factor that stimulates vascular and leaf development. IMPORTANCE While various mechanisms determine disease symptoms in plants depending on virus-host combinations, the details of how plant viruses induce symptoms remain largely unknown in most plant species. Kobu-sho is a disease in gentian that shows gall formation with ectopic development of lignified cells and vascular tissues such as xylem. Our findings demonstrate that a gene fragment of gentian Kobu-sho-associated virus (GKaV), which is designated as Kobu-sho-inducing factor, induces the gall formation accompanied by the ectopic development of lignified cells and xylem-like tissue in Nicotiana benthamiana. The molecular mechanism by which gentian Kobu-sho-associated virus induces the Kobu-sho symptoms will provide new insight into not only plant-virus interactions but also the regulatory mechanisms underlying vascular and leaf development.

Speciation in Nearctic oak gall wasps is frequently correlated with changes in host plant, host organ, or both.

Quantifying the frequency of shifts to new host plants within diverse clades of specialist herbivorous insects is critically important to understand whether and how host shifts contribute to the origin of species. Oak gall wasps (Hymenoptera: Cynipidae: Cynipini) comprise a tribe of ∼1000 species of phytophagous insects that induce gall formation on various organs of trees in the family Fagacae—primarily the oaks (genus Quercus; ∼435 sp.). The association of oak gall wasps with oaks is ancient (∼50 my), and most oak species are galled by one or more gall wasp species. Despite the diversity of both gall wasp species and their plant associations, previous phylogenetic work has not identified the strong signal of host plant shifting among oak gall wasps that has been found in other phytophagous insect systems. However, most emphasis has been on the Western Palearctic and not the Nearctic where both oaks and oak gall wasps are considerably more species rich. We collected 86 species of Nearctic oak gall wasps from most of the major clades of Nearctic oaks and sequenced >1000 Ultraconserved Elements (UCEs) and flanking sequences to infer wasp phylogenies. We assessed the relationships of Nearctic gall wasps to one another and, by leveraging previously published UCE data, to the Palearctic fauna. We then used phylogenies to infer historical patterns of shifts among host tree species and tree organs. Our results indicate that oak gall wasps have moved between the Palearctic and Nearctic at least four times, that some Palearctic wasp clades have their proximate origin in the Nearctic, and that gall wasps have shifted within and between oak tree sections, subsections, and organs considerably more often than previous data have suggested. Given that host shifts have been demonstrated to drive reproductive isolation between host‐associated populations in other phytophagous insects, our analyses of Nearctic gall wasps suggest that host shifts are key drivers of speciation in this clade, especially in hotspots of oak diversity. Although formal assessment of this hypothesis requires further study, two putatively oligophagous gall wasp species in our dataset show signals of host‐associated genetic differentiation unconfounded by geographic distance, suggestive of barriers to gene flow associated with the use of alternative host plants.

Identification of genes involved in Meloidogyne incognita-induced gall formation processes in Arabidopsis thaliana.

Root-knot nematodes (RKN; Meloidogyne incognita) are phytoparasitic nematodes that cause significant damage to crop plants worldwide. Recent studies have revealed that RKNs disrupt various physiological processes in host plant cells to induce gall formation. However, little is known about the molecular mechanisms of gall formation induced by nematodes. We have previously found that RNA expression levels of some of genes related to micro-RNA, cell division, membrane traffic, vascular formation, and meristem maintenance system were modified by nematode infection. Here we evaluated these genes importance during nematode infection by using Arabidopsis mutants and/or β-glucronidase (GUS) marker genes, particularly after inoculation with nematodes, to identify the genes involved in successful nematode infection. Our results provide new insights not only for the basic biology of plant-nematode interactions but also to improve nematode control in an agricultural setting.

De Novo Whole-Genome Assembly of the Swede Midge (Contarinia nasturtii), a Specialist of Brassicaceae, Using Linked-Read Sequencing.

The swede midge, Contarinia nasturtii, is a cecidomyiid fly that feeds specifically on plants within the Brassicaceae. Plants in this family employ a glucosinolate-myrosinase defense system, which can be highly toxic to nonspecialist feeders. Feeding by C. nasturtii larvae induces gall formation, which can cause substantial yield losses thus making it a significant agricultural pest. A lack of genomic resources, in particular a reference genome, has limited deciphering the mechanisms underlying glucosinolate tolerance in C. nasturtii, which is of particular importance for managing this species. Here, we present an annotated, scaffolded reference genome of C. nasturtii using linked-read sequencing from a single individual and explore systems involved in glucosinolate detoxification. The C. nasturtii genome is similar in size and annotation completeness to that of the Hessian fly, Mayetiola destructor, but has greater contiguity. Several genes encoding enzymes involved in glucosinolate detoxification in other insect pests, including myrosinases, sulfatases, and glutathione S-transferases, were found, suggesting that C. nasturtii has developed similar strategies for feeding on Brassicaceae. The C. nasturtii genome will, therefore, be integral to continued research on plant-insect interactions in this system and contribute to effective pest management strategies.

Range Expansion and Dispersal of the Asian Chestnut Gall Wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae) in the Mid-Atlantic States

The Asian chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu is an invasive species of global concern that was inadvertently introduced into North America where it induces gall formation on chestnut species including Castanea mollissima Blume, C. crenata Siebold & Zucc., and C. sativa Mill. as well as on the American chestnut, C. dentata (Marshall) Borkh. The gall former was introduced into the United States in the 1970's and since its initial introduction into Georgia, it has been reported to have spread to 13 other states. It has previously been documented as far to the northeast as Connecticut and Massachusetts and as far to the northwest as Michigan. Prior to this study it had been reported in 13 counties within the state of Pennsylvania. The introduction and spread of D. kuriphilus is of particular concern given the intensive efforts to restore American chestnuts into the North American landscape. The purpose of this study was to gain a better understanding of the distribution and spread of the Asian chestnut gall wasp in Eastern Pennsylvania and neighboring states. During the course of this study, specimens of Castanea spp. (Fagaceae) were assessed/monitored for the presence of galls caused by D. kuriphilus at over 100 sites in four states. Herein, galls caused by the Asian chestnut gall wasp are documented, for the first time, on Castanea spp. at several sites in the U.S. states of New Jersey, New York, and Delaware, new state records. Additionally, we report an expansion of the range of the Asian chestnut gall wasp to encompass twenty additional counties within Eastern Pennsylvania. Dispersal of the gall wasps in this study appears to have been influenced by topographical features and wind direction. For further confirmation of identity, we reared D. kuriphilus from galls collected at several sites. These findings establish the range expansion of this gall-forming invasive pest species in the United States to now encompass all of the Mid-Atlantic States.

Orange Leafhopper Cicadulina bipunctata Feeding Induces Gall Formation Nitrogen Dependently and Regulates Gibberellin Signaling.

Orange leafhopper Cicadulina bipunctata feeding induces wallaby ear symptoms, namely growth suppression and gall formation characterized by severe swelling of leaf veins, on various Poaceae, thereby leading to low crop yields. Here, we investigated the development of wallaby ear symptoms on rice seedlings due to C. bipunctata feeding. After confirming that C. bipunctata feeding induces growth suppression and gall formation on rice seedlings, we further demonstrated that gall formation score decreased with decreasing levels of nitrogen in the medium and that C. bipunctata feeding induces the expression levels of nitrogen transporter genes. These gene expression changes may participate in the nutrient accumulation observed in galled tissues and in gall formation. In addition, these expression changes should induce growth promotion but the inhibition of gibberellin signaling by C. bipunctata feeding might be the reason why growth is suppressed. Treatment with plant growth regulators did not affect gall formation, suggesting the existence of a complex gall formation mechanism by C. bipunctata feeding.

Root-knot nematodes induce gall formation by recruiting developmental pathways of post-embryonic organogenesis and regeneration to promote transient pluripotency.

Root-knot nematodes (RKNs; Meloidogyne spp.) induce new post-embryogenic organs within the roots (galls) where they stablish and differentiate nematode feeding cells, giant cells (GCs). The developmental programmes and functional genes involved remain poorly defined. Arabidopsis root apical meristem (RAM), lateral root (LR) and callus marker lines, SHORT-ROOT/SHR, SCARECROW/SCR, SCHIZORIZA/SCZ, WUSCHEL-RELATED-HOMEOBOX-5/WOX5, AUXIN-RESPONSIVE-FACTOR-5/ARF5, ARABIDOPSIS-HISTIDINE PHOSPHOTRANSFER-PROTEIN-6/AHP6, GATA-TRANSCRIPTION FACTOR-23/GATA23 and S-PHASE-KINASE-ASSOCIATED-PROTEIN2B/SKP2B, were analysed for nematode-dependent expression. Their corresponding loss-of-function lines, including those for LR upstream regulators, SOLITARY ROOT/SLR/IAA14, BONDELOS/BDL/IAA12 and INDOLE-3-ACETIC-ACID-INDUCIBLE-28/IAA28, were tested for RKN resistance/tolerance. LR genes, for example ARF5 (key factor for root stem-cell niche regeneration), GATA23 (which specifies pluripotent founder cells) and AHP6 (cytokinin-signalling-inhibitor regulating pericycle cell-divisions orientation), show a crucial function during gall formation. RKNs do not compromise the number of founder cells or LR primordia but locally induce gall formation possibly by tuning the auxin/cytokinin balance in which AHP6 might be necessary. Key RAM marker genes were induced and functional in galls. Therefore, the activation of plant developmental programmes promoting transient-pluripotency/stemness leads to the generation of quiescent-centre and meristematic-like cell identities within the vascular cylinder of galls. Nematodes enlist developmental pathways of new organogenesis and/or root regeneration in the vascular cells of galls. This should determine meristematic cell identities with sufficient transient pluripotency for gall organogenesis.

Shift of Feeding Mode in an Epizoic Stalked Barnacle Inducing Gall Formation of Host Sea Urchin.

SummaryAmong diverse stalked barnacles, Rugilepas pearsei (Thoracica: Cirripedia: Arthropoda) is a rare unique species that is associated with echinoids and has highly atrophied cirri. We rediscovered the barnacle for the first time from description and verified that the barnacles live obligately in half-open galls formed on the test of the sea urchin Echinothrix diadema (Diadematidae: Echinodermata). A molecular phylogenetic analysis demonstrated that the obligate association with echinoids derived from epizoic life on crustaceans. A stable isotope analysis suggests that the barnacle feeds on particulate organic matter (POM) without parasitizing the host echinoids. These findings suggest that the host shift caused losses of plates and feather-like cirri, changes in the attachment device from cementation to anchoring, and a shift in feeding mode from filter feeding to POM collection. The barnacle's epizoic, superficially sub-endozoic, communal life in stout but narrow galls causes repetitive reproduction at the cost of reduced growth.

Pest categorisation of Thecaphorasolani.

The Panel on Plant Health performed a pest categorisation of the fungus Thecaphora solani, the causal agent of smut of potato, for the EU. The identity of the pest is well established and reliable methods exist for its detection and identification. T. solani is present in Bolivia, Chile, Colombia, Ecuador, Mexico, Panama, Peru and Venezuela. The pathogen is not known to occur in the EU and is listed in Annex IAI of Directive 2000/29/EC, meaning its introduction into the EU is prohibited. The major host is Solanum tuberosum (potato), but various other tuber‐forming Solanum species are also affected. The pest has also been reported on Solanum lycopersicum (tomato), and wild solanaceous plants are also affected. All the major hosts and pathways of entry are currently regulated. Host availability and climate matching suggest that T. solani could establish in parts of the EU and further spread by human‐assisted means. The disease induces gall formation on potato tubers, stolons and underground stem parts, reducing yield and making tubers unmarketable. The pest introduction in the EU would potentially cause impacts to potato production. In the infested areas, the only available strategy to control the disease and prevent it from spreading is the application of quarantine and sanitation measures and the cultivation of resistant varieties. The main uncertainties concern the host range, the biology and epidemiology of the pest, and the potential of the pest to enter the EU through three unregulated minor pathways. T. solani meets all the criteria assessed by EFSA for consideration as potential Union quarantine pest. The criteria for considering T. solani as a potential Union regulated non‐quarantine pest are not met, since the pest is not known to occur in the EU.

An insect nucleoside diphosphate kinase (NDK) functions as an effector protein in wheat - Hessian fly interactions

Like pathogens, galling insects deliver effectors into plant tissues that induce gall formation. The gall midge Mayetiola destructor, also called Hessian fly, can convert a whole wheat seedling into a gall by inducing the formation of nutritive cells at the feeding site, inhibiting wheat growth, and reprogramming metabolic pathways of the attacked plants. Here we demonstrated the identification of a secreted Hessian fly protein, the nucleoside diphosphate kinase (NDK), in infested wheat plants through liquid chromatography-tandem mass spectrometry (LC-MS/MS) and western blots. In association with the NDK presence, enzymatic activity of NDK increased significantly in wheat tissues at the feeding site. In addition, there was a sudden increase in ATP abundance at the feeding site of infested susceptible wheat seedlings 24 h following Hessian fly larval infestation. Even though a direct link between cause and effect remains to be established, our data points to the direction that Hessian fly larvae injected NDK into wheat tissues as an effector protein, which plays a role in manipulating host plants and converting the plants into galls.

Quorum Sensing and Quorum Quenching in Agrobacterium: A "Go/No Go System"?

The pathogen Agrobacterium induces gall formation on a wide range of dicotyledonous plants. In this bacteria, most pathogenicity determinants are borne on the tumour inducing (Ti) plasmid. The conjugative transfer of this plasmid between agrobacteria is regulated by quorum sensing (QS). However, processes involved in the disturbance of QS also occur in this bacteria under the molecular form of a protein, TraM, inhibiting the sensing of the QS signals, and two lactonases BlcC (AttM) and AiiB that degrade the acylhomoserine lactone (AHL) QS signal. In the model Agrobacterium fabrum strain C58, several data, once integrated, strongly suggest that the QS regulation may not be reacting only to cell concentration. Rather, these QS elements in association with the quorum quenching (QQ) activities may constitute an integrated and complex “go/no go system” that finely controls the biologically costly transfer of the Ti plasmid in response to multiple environmental cues. This decision mechanism permits the bacteria to sense whether it is in a gall or not, in a living or decaying tumor, in stressed plant tissues, etc. In this scheme, the role of the lactonases selected and maintained in the course of Ti plasmid and agrobacterial evolution appears to be pivotal.

Plant development reprogramming by cynipid gall wasp: proteomic analysis

An insect–plant interaction induced gall formation is where gall wasps change the plant development towards formation of new units to shield and nourish the evolving larvae. The targets of the insect signals and the mechanism of gall development are unknown. To show the molecular pathways that are responsive to the gall wasp, the proteomic approach was used to compare the gall with non-gall plant tissues. We studied three oak gall species (Cynips quercusfolii, Cynips longiventris, and Neuroterus quercusbaccarum) and the host plant (Quercus robur). Among the 21 identified proteins, 18 increased and three decreased in abundance in gall tissue, in comparison to the leaf tissues. Ten proteins were C. quercusfolii responsive, two only with this gall inducer, while seven increased in abundance. Eleven proteins were C. longiventris responsive, and two only with this gall inducer. Sixteen proteins were associated with gall formation by the N. quercusbaccarum and, in this, eight only with this gall inducer. A similar effect on protein abundance occurred as galls in leaf veins (for five proteins). For leaf blades, such a relation was not found. The role of each protein is discussed according to its involvement in the gall formation. Moreover, S-adenosyl methionine synthase, flavone 3-hydroxylase, stress- and pathogenesis-related proteins, and gamma carbonic anhydrase are associated with developmental regulation of plant tissue into a gall.

Differences in Monoterpene Biosynthesis and Accumulation in Pistacia palaestina Leaves and Aphid-Induced Galls.

Certain insect species can induce gall formation on numerous plants species. Although the mechanism of gall development is largely unknown, it is clear that insects manipulate their hosts' anatomy, physiology, and chemistry for their own benefit. It is well known that insect-induced galls often contain vast amounts of plant defensive compounds as compared to non-colonized tissues, but it is not clear if defensive compounds can be produced in situ in the galled tissues. To answer this question, we analyzed terpene accumulation patterns and possible independent biosynthetic potential of galls induced by the aphid Baizongia pistaciae L. on the terminal buds of Pistacia palaestina Boiss. We compared monoterpene levels and monoterpene synthase enzyme activity in galls and healthy leaves from individual trees growing in a natural setting. At all developmental stages, monoterpene content and monoterpene synthase activity were consistently (up to 10 fold on a fresh weight basis) higher in galls than in intact non-colonized leaves. A remarkable tree to tree variation in the products produced in vitro from the substrate geranyl diphosphate by soluble protein extracts derived from individual trees was observed. Furthermore, galls and leaves from the same trees displayed enhanced and often distinct biosynthetic capabilities. Our results clearly indicate that galls possess independent metabolic capacities to produce and accumulate monoterpenes as compared to leaves. Our study indicates that galling aphids manipulate the enzymatic machinery of their host plant, intensifying their own defenses against natural enemies.

Description of a new endoparasitic copepod genus and species (Lamippidae) that induces gall formation in leaves of the sea pen Ptilosarcus gurneyi (Octocorallia) from British Columbia

A new genus and species of gall-forming endoparasitic copepod of the family Lamippidae is described from the orange sea pen Ptilosarcus gurneyi (Gray, 1860) collected in British Columbia, Canada. Lamippid copepods (over 50 species) are obligate endoparasites, some of which form galls in a variety of soft corals (Alcyonacea and Pennatulacea). Ptilosarcoma athyrmata n. gen., n. sp. is the first lamippid formally described from any species of Ptilosarcus Verrill, 1865. In total, 143 galls from six sea pens were dissected and found to typically contain one female and male copepod pair. Infested leaves of P. gurneyi had 1.4 ± 0.6 (n = 143) galls per leaf. Using light and scanning electron microscopy, the copepods were examined and found to most closely resemble those belonging to the genus Isidicola Gravier, 1914, based on the presence of maxillipeds and lack of acicules on the caudal rami; however, they are distinct from the sole species of Isidicola based on aspects of antennal morphology. We conclude that Lamippina laubieri Bouligand, 1960 is a synonym of L. aciculifera (Zulueta, 1908), thus the family presently contains 52 species and one subspecies. A key to lamippid genera and a table of all lamippid genera and species with all known hosts and locality records are provided.

Arabidopsis Mutant bik1 Exhibits Strong Resistance to Plasmodiophora brassicae.

Botrytis-induced kinase1 (BIK1), a receptor-like cytoplasmic kinase, plays an important role in resistance against pathogens and insects in Arabidopsis thaliana. However, it remains unknown whether BIK1 functions against Plasmodiophora brassicae, an obligate biotrophic protist that attacks cruciferous plants and induces gall formation on roots. Here, we investigated the potential roles of receptors FLS2, BAK1, and BIK1 in the infection of P. brassicae cruciferous plants. Wild-type plants, fls2, and bak1 mutants showed typical symptom on roots, and the galls were filled with large quantities of resting spores, while bik1 mutant plants exhibited strong resistance to P. brassicae. Compared with that of the wild-type plants, the root hair and cortical infection rate of bik1 mutant were significantly reduced by about 40–50%. A considerable portion of bik1 roots failed to form typical galls. Even if some small galls were formed, they were filled with multinucleate secondary plasmodia. The bik1 plants accumulated less reactive oxygen species (ROS) at infected roots than other mutants and wild-type plants. Exogenous salicylic acid (SA) treatment alleviated the clubroot symptoms in wild-type plants, and the expression of the SA signaling marker gene PR1 was significantly increased in bik1. Both sid2 (salicylic acid induction-deficient 2) and npr1-1 [non-expresser of PR genes that regulate systemic acquired resistance (SAR)] mutants showed increased susceptibility to P. brassicae compared with wild-type plants. These results suggest that the resistance of bik1 to P. brassicae is possibly mediated by SA inducible mechanisms.

Reversal of mutualism in a leafflower-leafflower moth association: the possible driving role of a third-party partner

A major goal in the study of mutualism is to understand how co-operation is maintained when mutualism may potentially turn into parasitism. Although certain mechanisms facilitate the persistence of mutualism, parasitic species have repeatedly evolved from mutualistic ancestors. However, documented examples of mutualism reversals are still rare. Leafflowers (Phyllantheae; Phyllanthaceae) include approximately 500 species that engage in obligate mutualism with leafflower moths (Epicephala; Gracillariidae), which actively pollinate flowers, and whose larvae feed on the resulting seeds. We found that the Taiwanese population of the Phyllanthus reticulatus species complex was associated with six sympatric Epicephala species, of which three were derived parasites that induced gall formation on flowers/buds and produced no seeds. Notably, two parasitic species have retained mutualistic pollination behaviour, suggesting that the parasitism was likely not selected for to reduce the cost of mutualism. We propose that the galling habit evolved as an adaptation to escape parasitism by a specialized braconid wasp. The tough gall produced by one species was almost free of braconid parasitism, and the swollen gall induced by the other species probably prevents attack as a result of the larger airspace inside the gall. Our findings suggest that the presence of a third-party partner can greatly influence the evolutionary fate of mutualisms, regardless of whether the pairwise interaction continues to favour co-operation.

Aboveground insect infestation attenuates belowground Agrobacterium-mediated genetic transformation.

Agrobacterium tumefaciens causes crown gall disease. Although Agrobacterium can be popularly used for genetic engineering, the influence of aboveground insect infestation on Agrobacterium induced gall formation has not been investigated. Nicotiana benthamiana leaves were exposed to a sucking insect (whitefly) infestation and benzothiadiazole (BTH) for 7d, and these exposed plants were inoculated with a tumorigenic Agrobacterium strain. We evaluated, both in planta and in vitro, how whitefly infestation affects crown gall disease. Whitefly-infested plants exhibited at least a two-fold reduction in gall formation on both stem and crown root. Silencing of isochorismate synthase 1 (ICS1), required for salicylic acid (SA) synthesis, compromised gall formation indicating an involvement of SA in whitefly-derived plant defence against Agrobacterium. Endogenous SA content was augmented in whitefly-infested plants upon Agrobacterium inoculation. In addition, SA concentration was three times higher in root exudates from whitefly-infested plants. As a consequence, Agrobacterium-mediated transformation of roots of whitefly-infested plants was clearly inhibited when compared to control plants. These results suggest that aboveground whitefly infestation elicits systemic defence responses throughout the plant. Our findings provide new insights into insect-mediated leaf-root intra-communication and a framework to understand interactions between three organisms: whitefly, N.benthamiana and Agrobacterium.

Use of the arbuscular mycorrhizal fungus Glomus intraradices as biological control agent of the nematode Nacobbus aberrans parasitizing tomato

ABSTRACT The plant-parasitic nematode Nacobbus aberrans is an endoparasite that induces gall formation in the roots and causes severe losses to diverse crops. Some populations of this nematode show preference for certain hosts, revealing the existence of “races/groups” with diff erent behaviour and making nematode management difficult. A possible biological control alternative to reduce the damage caused by this species may be the use of arbuscular mycorrhizal fungi (AMF). In the present work, the effect of Glomus intraradices on tomato plants inoculated with the nematode at transplanting and three weeks later was tested. At 60 days, the following parameters were estimated: percentage of AMF colonization, root and aerial dry weight, number of galls and egg masses, and reproduction factor (RF=final population/initial population) of N. aberrans . AMF colonization was higher in the presence of the nematode. The use of AMF favoured tomato biomass and reduced the number of galls and RF on the plants inoculated with the nematode at transplanting. Key words: arbuscular mycorrhiza, false root-knot nematode, microbiological control, plant protection

EST Sequencing of Meloidogyne javanica Infected Pineapple Root Tissues Reveals Changes in Gene Expression during Root-Knot Nematode Induced Gall Formation

An expressed sequence tag project has been performed to survey a range of expressed sequences in the vascular cylinder tissue of pineapple roots infected with the root-knot nematode Meloidogyne javanica. A total of 4,102 EST sequences were obtained, comprising of 1,298 early infection clones, 2,461 late infection clones and 343 non-infected root tip clones. Clone redundancy was 34.4 %, with the 4,102 EST sequences clustering into 2,976 contigs comprising of 286 clusters and 2,690 singletons. A comparison of the most abundant clones isolated from the early and late infection libraries revealed significant differences in the transcriptomes of the vascular cylinder at early and late infection stages. Northern analysis and quantitative real time PCR confirmed a variety of genes including a metallothinein-like protein, an alpha tubulin, a phosphoglyceratemutase, a glyceradehyde phosphate dehydrogenase, a mannose-binding lectin and four previously undiscovered sequences are differentially expressed during gall formation. Analysis of clone distribution by functional classification revealed that the late infection library contains a higher proportion of clones associated with oxidative stress responses and the detoxification of free radicals. The EST and contig sequence collection, bioinformatic data and functional classification information is available through an online pineapple database resource housed at http://genet.imb.uq.edu.au/Pineapple/index.html.