The interplay between a Phytophthora RXLR effector and an Arabidopsis lectin receptor kinase

Phytophthora infestans – the causal agent of potato late blight – secretes a plethora of effector proteins to facilitate plant infection. The central subject of this thesis is ipiO, one of the first cloned Phytophthora genes with a putative function in pathogenicity as was anticipated based on its in planta induced (ipi) expression, in particular during early stages of host infection. IPI-O contains two striking motifs: RXLR-dEER and RGD. RGD is a cell adhesion motif and was shown to be involved in binding to the extracellular lectin domain of LecRK-I.9, a lectin receptor kinase of Arabidopsis. The RXLR-dEER motif plays a role in effector trafficking into host cells and is shared by several secreted oomycete effector proteins which are known to function as race-specific avirulence (Avr) factors. In a previous study, that was aimed at identifying novel pairs of P. infestans Avr and host plant resistance (R) genes, a high-throughput effector genomics screen identified ipiO as Avr-blb1, the counterpart of the late blight R gene Rpi-blb1 which originates from the nightshade Solanum bulbocastanum. Often R genes exploited in late blight resistance breeding become rapidly ineffective as a result of adaptation of P. infestans. However, unlike most late blight R genes that interact in a gene-for-gene manner with Avr genes, Rpi-blb1 seemed to have the potential to remain its effectiveness. In section 2 we monitored the genetic variation and distribution of the ipiO family in an extensive isolate collection of P. infestans and closely related species. This resulted in the identification of 16 IPI-O variants that could be sub-divided in three distinct classes. Variants from class I and class II were shown to induce cell death when co-infiltrated with Rpi-blb1 in Nicotiana benthamiana. Class III consists solely of the highly divergent variant IPI-O4, that is not able to trigger Rpi-blb1-mediated cell death. Class I is highly diverse and represented in all P. infestans isolates analyzed so far, except in two Mexican P. infestans isolates. The latter two are capable to infect Rpi-blb1 plants, suggesting that the lack of class I variants in the genome of these strains allows them to escape recognition by Rpi-blb1 plants. We propose that profiling of the ipiO variants within P. infestans populations can predict the effectiveness of Rpi-blb1-mediated resistance in potato and, as such, can facilitate integrated disease management. Section 3 of this thesis deals with legume-like lectin receptor kinases (LecRKs), membrane-spanning proteins with potential roles in adaptive responses and cell wall integrity. We present an inventory and a phylogenetic analysis of the Arabidopsis LecRK gene family. The rationale behind this study was to gain better insight into the diversity of LecRKs and their potential roles in plant defense. A comprehensive expression analysis based on exploration of existing databases revealed that several LecRK genes are induced upon treatment with elicitors or during pathogen infection. Based on the phylogenetic analysis we have reclassified the LecRK genes and proposed a new nomenclature. LecRK-I.9, one of the clade I Arabidopsis LecRKs which binds the RGD cell adhesion motif of IPI-O, was shown to mediate adhesion between the cell wall (CW) and plasma membrane (PM). In contrast, IPI-O disrupts these adhesions by virtue of its RGD motif. We analyzed Arabidopsis LecRK-I.9 knock-out lines (lecrk-I.9) for their response to pathogen infection, in particular to Phytophthora brassicae. We also analyzed transgenic Arabidopsis lines expressing ipiO, and observed that both the ipiO-expressing lines and lecrk-I.9 lines are impaired in their resistance to oomycete pathogens. To unravel the mechanisms underlying this phenomenon we analysed callose deposition upon MAMP (i.e. flg22) treatment and investigated the strength of CW-PM adhesions under plasmolysis-inducing conditions. The results indicated that LecRK-I.9 is not only important for the maintenance of the CW-PM continuum, but also in MAMP-triggered immunity. Also here, both the ipiO-expressing lines and the lecrk-I.9 knock-outs displayed a destabilized CW-PM continuum and impaired callose deposition, and hence, they can be regarded as phenocopies. Arabidopsis plants that constitutively express LecRK-I.9 were smaller in size, and displayed increased levels of anthocyanin and lignin. Additionally, these lines were shown to exhibit enhanced resistance to P. brassicae. Furthermore, we studied transgenic potatoes that constitutively Arabidopsis LecRK-I.9. In comparison to the parental control potato line the transgenic lines were less susceptible to mild and moderately aggressive P. infestans isolates, but the increased tolerance was not sufficient to provide resistance to aggressive isolates. These results strongly suggest that LecRK-I.9 is a novel resistance component that plays a role in defense against Phytophthora. In Section 4 we describe a novel method for propagating P. brassicae zoospores on an intermediate host plant. This resulted in the production of high numbers of zoospores thereby facilitating highly reproducible small and large scale inoculation experiments. This thesis is completed with a general discussion (Section 5) addressing the current understanding of effector uptake by host cells, the subsequent recognition by cognate R proteins mediating effector-triggered immunity, and RXLR-dEER effector diversity. We also discuss the role of the RGD motif in effectors of both animal and plant pathogens, and the potential functions of LecRKs. Finally, we high-light the advantages of Arabidopsis-Phytophthora pathosystems as research object. <br/

Quantum random walk of two photons in separable and entangled state

We discuss quantum random walk of two photons using linear optical elements. We analyze the quantum random walk using photons in a variety of quantum states including entangled states. We find that for photons initially in separable Fock states, the final state is entangled. For polarization entangled photons produced by type II downconverter, we calculate the joint probability of detecting two photons at a given site. We show the remarkable dependence of the two photon detection probability on the quantum nature of the state. In order to understand the quantum random walk, we present exact analytical results for small number of steps like five. We present in details numerical results for a number of cases and supplement the numerical results with asymptotic analytical results

Entanglement Purification through Zeno-like Measurements

We present a novel method to purify quantum states, i.e. purification through Zeno-like measurements, and show an application to entanglement purification.Comment: 5 pages, 1 figure; Contribution to the Proceedings of "Mysteries, Puzzles and Paradoxes in Quantum Mechanics", Gargnano, Italy, 2003 (to be published in J. Mod. Opt.

Understanding phoneme segmentation performance by analyzing abilities and word properties

Several studies have demonstrated the relationship between phoneme segmentation ability and early reading performance, but so far it is unclear which abilities are involved, and which word properties contribute to the difficulty level of a segmentation task. Using a sample of 596 Dutch children, we investigated the abilities involved in segmenting the phonemes of 45 pseudowords that differed with respect to several properties. First, we found that a combination of short-term memory and speech perception explained variation in segmentation performance. Second, we found that a limited number of word property effects explained the difficulty level of pseudowords rather well. Finally, we constructed a high-reliability scale for measuring segmentation ability. </jats:p

Experimental violation of a spin-1 Bell inequality using maximally-entangled four-photon states

We demonstrate the first experimental violation of a spin-1 Bell inequality. The spin-1 inequality is a calculation based on the Clauser, Horne, Shimony and Holt formalism. For entangled spin-1 particles the maximum quantum mechanical prediction is 2.552 as opposed to a maximum of 2, predicted using local hidden variables. We obtained an experimental value of 2.27 $\pm 0.02$ using the four-photon state generated by pulsed, type-II, stimulated parametric down-conversion. This is a violation of the spin-1 Bell inequality by more than 13 standard deviations.Comment: 5 pages, 3 figures, Revtex4. Problem with figures resolve

Quantum decoherence in noninertial frames

Quantum decoherence, which appears when a system interacts with its environment in an irreversible way, plays a fundamental role in the description of quantum-to-classical transitions and has been successfully applied in some important experiments. Here, we study the decoherence in noninertial frames for the first time. It is shown that the decoherence and loss of the entanglement generated by the Unruh effect will influence each other remarkably. It is interesting to note that in the case of the total system under decoherence, the sudden death of entanglement may appear for any acceleration. However, in the case of only Rob's qubit underging decoherence sudden death may only occur when the acceleration parameter is greater than a "critical point."Comment: 4 pages, 3 figure

Minimum cbits for remote preperation and measurement of a qubit

We show that a qubit chosen from equatorial or polar great circles on a Bloch spehere can be remotely prepared with one cbit from Alice to Bob if they share one ebit of entanglement. Also we show that any single particle measurement on an arbitrary qubit can be remotely simulated with one ebit of shared entanglement and communication of one cbit.Comment: Latex, 7 pages, minor changes, references adde