Dissecting host plant manipulation by cyst and root-knot nematodes

Cyst ( Globodera spp. and Heterodera spp.) and root-knot nematodes ( Meloidogyne spp.), one of the most damaging crop pests, are a perfect example of highly adapted, sophisticated root parasites. These nematodes induces specialized feeding structures (cyst nematodes-syncytia, root-knot nematode-giant cells) within the host root and benefits from guaranteed continues supply of food and water from their host plant and protection within the cyst or gall for their progeny. This dissertation aims at elucidation of the molecular mechanisms controlling the induction and maintenance of those feeding structures. This knowledge is indispensable to make novel advances in constructing durable host plant resistance.A number of different observations suggested a primary role of the phytohormone auxin in the feeding cell development. However, it has never been directly proven. Therefore, we have used the DR5 promoter element fused to gusA reporter gene to visualize spatial and temporal changes in auxin distribution, during nematode infection in Arabidopsis thaliana roots infected with cyst or root-knot nematodes. DR5 promoter element is considered to be a specific indicator for auxin and is activation points at an increase of the perceived auxin concentration. For both, cyst and root-knot nematode species, strong GUS expression was observed at the very onset of parasitism, already at 18 hours post inoculation. This high expression level was maintained until 3-5 days post inoculation and then gradually was reduced. Semi-thin sections of infected roots were investigated microscopically, revealing the presence of GUS inside the initial cells, and in case of cyst nematodes, in cells to-be incorporated into syncytium. This implies that expansion of syncytium is marked by the regions with high gusA expression. Activation of DR5 promoter element can be explained by: an accumulation or an increased sensitivity to auxin. However, based on formerly gathered data, a local accumulation seems to be the more probable explanation. Moreover, the feeding structures of cyst and root-knot nematodes arise by distance mechanisms, hence the highly similar DR5 activation patterns in both feeding structures, is remarkable. This promptthe conclusion that notwithstanding the highly dissimilar structure and ontogeny, both nematodes interfere with similar signal transduction pathways in root morphogenesis.Apart from phytohormones, small peptide signalling plays a very important role in diverse aspects of plant growth and development, and such a molecule(s) could be potentially involved in the establishment of nematode feeding cell. Early nodulin ( ENOD ) genes have been defined as genes expressed in legumes during nodule formation. Recent studies, however, revealed a number of homologues of ENOD40 s in non-legume plants. In both plants types, ENOD40 expression associates with the development of the vascular tissue. Feeding site development by root-knot and cyst nematodes is accompanied by the distortion of the vascular tissue, therefore a local increase in ENOD40 expression could be anticipated. This holds truth in interaction between legume Medicago truncatula and root-knot nematodes. However, in non-legume tomato infected with cyst and root-knot nematodes, no change in ENOD40 transcript levels could be detected using RT-PCR. In addition, activation of the Sl-ENOD40 promoter was only observed in infected regions showing endogenous ENOD40 expression. Similar results were obtained for a legume ENOD40 promoter (soybean) in a non-legumes background ( Arabidopsis ), and - contrary to M. truncatula - over-expression of Gm-ENOD40 in Arabidopsis had no effect on nematode development. Hence, ENOD40 expression in tomato is basically unaffected by the induction of feeding sites by root-knot and cyst nematodes. This unexpected difference in nematode-induced ENOD40 is apparently plant background-dependent, and suggests the existence of a legume-specific factor that boosts the ENOD40 expression in legume hosts-nematode interaction.One of the most striking characteristic of the cyst nematode induced feeding structure (syncytium) is the extensive cell wall dissolution, as the syncytium expands towards the vascular bundle and along the xylem vessels. Endo-1,4-ß-glucanases (cellulases) reside among plant enzymes that are involved in this progressive cell wall dissolution.RT-PCR experiments in tomato revealed that the potato cyst nematode induces the expression of two out of the eight described cellulases, precisely, Sl-cel7 and Sl-cel8 . In situ hybridization and immunodetection studies showed that both cellulases are expressed inside and adjacent to nematode-induced syncytia. Transgenic potato plants carryinghpRNA-silencing constructs for cel7 and cel8 were infected with cyst nematode which resulted in a significant arrest of cyst nematodes development.Reduced development of juveniles into females (up to 60%) and increase in the fraction of females without eggs (up to 89%) was observed. This indicates that the recruitment of specific plant cellulases by potato cyst nematodes is essential for their development, and demonstrates how detailed knowledge of compatible plant-parasite relationships can lead to host plant resistance.The genomic sequence of potato, cel7 and cel8a was cloned and characterised, in order to enable the RNA interference experiments in the natural host of potato cyst nematodes. The analysis of sequences suggests the presence of multiple isoforms of cel8 in potato. That corresponding proteins consist solely of a catalytic core domain (St-CEL7) or of a catalytic domain linked to a carbohydrate binding module (CBM) (St-CEL8a). Only recently, the CBM domain of Sl-CEL8a was shown to belong to CBM family 2 and on the basis of shared features between CBM domains in Sl-CEL8 and St-CEL8a it can be concluded that St-CEL8a harbours a cellulose binding domain as well. Therefore, those findings imply that the potato cellulases recruited by the potato cyst nematode are able to hydrolyse both xyloglucan (CEL7) and crystalline cellulose (CEL8), and apart from cloning novel potato cellulases genes, provides an explanation why nematodes recruit exactly these two members of the cellulase family. Moreover, potato cellulase sequences were used to mine EST databases and this information was used for the generation of a phylogenetic tree of the Solanaceous endo-β-1,4-D-glucanase gene family. In this dissertation we take an effort to understand better the intimae relationship between the obligatory plant parasites, cyst and root-knot nematodes and host plants. We show that such a detailed knowledge can be beneficial in better understanding of plant physiology and can be used as a highly specific and bio-safe approach for pathogen management

Tachyon Backgrounds in 2D String Theory

We consider the construction of tachyonic backgrounds in two-dimensional string theory, focusing on the Sine-Liouville background. This can be studied in two different ways, one within the context of collective field theory and the other via the formalism of Toda integrable systems. The two approaches are seemingly different. The latter involves a deformation of the original inverted oscillator potential while the former does not. We perform a comparison by explicitly constructing the Fermi surface in each case, and demonstrate that the two apparently different approaches are in fact equivalent.Comment: 25 pages, no figure

Condensing Momentum Modes in 2-d 0A String Theory with Flux

We use a combination of conformal perturbation theory techniques and matrix model results to study the effects of perturbing by momentum modes two dimensional type 0A strings with non-vanishing Ramond-Ramond (RR) flux. In the limit of large RR flux (equivalently, mu=0) we find an explicit analytic form of the genus zero partition function in terms of the RR flux $q$ and the momentum modes coupling constant alpha. The analyticity of the partition function enables us to go beyond the perturbative regime and, for alpha>> q, obtain the partition function in a background corresponding to the momentum modes condensation. For momenta such that 0<p<2 we find no obstruction to condensing the momentum modes in the phase diagram of the partition function.Comment: 22 page

Quadratic alpha' corrections to T-duality

The quadratic alpha' corrections to the two-dimensional black hole and to its T-dual are calculated. These backgrounds are used to write the covariant form of the quadratic alpha' corrections to the T-duality for general time-dependent backgrounds of dilaton and diagonal metric in the bosonic string theory.Comment: 15 pages, JHEP; typos corrected, references adde

Solution of a class of the first kind singular integral equation with multiplicative Cauchy kernel

In the present paper, we give the exact solutions of a singular equation with logarithmic singularities in two classes of functions and construct formulae for the approximate solutions

Survivin antiapoptotic gene expression as a prognostic factor in non-small cell lung cancer: in situ hybridization study.

Survivin is an inhibitor of apoptosis that plays a significant role in cell cycle regulation and is important for survival prognosis in many neoplasms. Survivin expression was assessed by in situ hybridization (ISH) in 60 consecutive patients (54 males and 4 females) with NSCLC treated between 1993 and 1997. The examined patients had IIB and IIIA stage according to TNM system. In all cases the chemotherapy with cisplatin and etoposide (2 cycles) was administered prior the surgery; in patients responding to the therapy one more cycle was applied. Survivin gene overexpression was observed in 35 patients (58.3%). There was no correlation between survivin mRNA level and histological type of tumor, stage of cell differentiation, stage of disease according to TNM classification, performance status according to WHO and number of chemotherapy regimens administered (p > 0.05). However, the correlation between survivin gene expression and response to the chemotherapy was statistically significant (p = 0.04). Statistical analysis showed that median survival in patients with survivin gene overexpression was shorter (14.0 months) as compared to patients with no expression (60.0 months; p = 0.00002). In survival assessment by means of Kaplan-Meier test, 14.3% of five-year survival was achieved in the former group versus 60% in the latter (p = 0.00003). Univariate analysis (log-rank test) showed that significant independent prognostic factors in NSCLC included: stage of the disease according to TNM classification (p = 0.006), response to chemotherapy (p = 0.005) and pattern of survivin gene expression (p = 0.00003). Multivariate analysis utilizing Cox's model showed that for survival assessment the stage according to TNM, response to the chemotherapy and survivin expression estimated by means of ISH are of statistical significance (p=0.00001). The calculated predictive values showed that ISH technique was quite accurate in assessment of five-year survival. Our data show that survivin expression may be used as a prognostic factor and a target for therapy

Energy Quantisation in Bulk Bouncing Tachyon

We argue that the closed string energy in the bulk bouncing tachyon background is to be quantised in a simple manner as if strings were trapped in a finite time interval. We discuss it from three different viewpoints; (1) the timelike continuation of the sinh-Gordon model, (2) the dual matrix model description of the (1+1)-dimensional string theory with the bulk bouncing tachyon condensate, (3) the c_L=1 limit of the timelike Liouville theory with the dual Liouville potential turned on. There appears to be a parallel between the bulk bouncing tachyon and the full S-brane of D-brane decay. We find the critical value \lambda_c of the bulk bouncing tachyon coupling which is analogous to \lambda_o=1/2 of the full S-brane coupling, at which the system is thought to be at the bottom of the tachyon potential.Comment: 25 pages, minor changes, one reference adde

Large Representation Recurrences in Large N Random Unitary Matrix Models

In a random unitary matrix model at large N, we study the properties of the expectation value of the character of the unitary matrix in the rank k symmetric tensor representation. We address the problem of whether the standard semiclassical technique for solving the model in the large N limit can be applied when the representation is very large, with k of order N. We find that the eigenvalues do indeed localize on an extremum of the effective potential; however, for finite but sufficiently large k/N, it is not possible to replace the discrete eigenvalue density with a continuous one. Nonetheless, the expectation value of the character has a well-defined large N limit, and when the discreteness of the eigenvalues is properly accounted for, it shows an intriguing approximate periodicity as a function of k/N.Comment: 24 pages, 11 figure

c < 1 String from Two Dimensional Black Holes

We study a topological string description of the c < 1 non-critical string whose matter part is defined by the time-like linear dilaton CFT. We show that the topologically twisted N=2 SL(2,R)/U(1) model (or supersymmetric 2D black hole) is equivalent to the c < 1 non-critical string compactified at a specific radius by comparing their physical spectra and correlation functions. We examine another equivalent description in the topological Landau-Ginzburg model and check that it reproduces the same scattering amplitudes. We also discuss its matrix model dual description.Comment: 36 pages, harvmac; acknowledgements, comments and references adde