Gabriella Varga

Novel Extracellular Chitinases Rapidly and Specifically Induced by General Bacterial Elicitors and Suppressed by Virulent Bacteria as a Marker of Early Basal Resistance in Tobacco

Early basal resistance (EBR, formerly known as early induced resistance) is triggered by general bacterial elicitors. EBR has been suggested to inhibit or retard expression of the type III secretion system of pathogenic bacteria and may also prevent nonpathogenic bacteria from colonizing the plant tissue. The quickness of EBR here plays a crucial role, compensating for a low bactericidal efficacy. This inhibitory activity should take place in the cell wall, as bacteria do not enter living plant cells. We found several soluble proteins in the intercellular fluid of tobacco leaf parenchyma that coincided with EBR under different environmental (light and temperature) conditions known to affect EBR. The two most prominent proteins proved to be novel chitinases (EC 3.2.1.14) that were transcriptionally induced before and during EBR development. Their expression in the apoplast was fast and not stress-regulated as opposed to many pathogenesis-related proteins. Nonpathogenic, saprophytic, and avirulent bacteria all induced EBR and the chitinases. Studies using these chitinases as EBR markers revealed that the virulent Pseudomonas syringae pv. tabaci, being sensitive to EBR, must suppress it while suppressing the chitinases. EBR, the chitinases, as well as their suppression are quantitatively related, implying a delicate balance determining the outcome of an infection.

Identification of Virulence-Associated Genes of Pseudomonas viridiflava Activated During Infection by Use of a Novel IVET Promoter Probing Plasmid

Analysis of virulence mechanisms of plant pathogens is often limited by the lack of genetic tools that can be used to identify genes that are preferentially expressed during their interactions with plants. In the present study, we used the newly constructed IVET (in vivoexpression technique) plasmid pIviGK and the corresponding antibiotic resistance–based selection method to identify genes that encode pathogenicity factors of the soft rot-causing bacterium Pseudomonas viridiflava. These included pel, the gene encoding pectate lyase, which is responsible for the development of soft rot symptoms. We have also isolated and characterized the gene mviNpv encoding a putative novel membrane associated virulence factor of P. viridiflava. A mutation in mviNpv was shown to influence motility as well as virulence of P. viridiflava. The mviNpv gene is expressed to a moderate level in LB media and its expression increases under inducing conditions as was shown by measuring in planta expression dynamics of the fused gfp reporter gene.

ℒ 2 -gain analysis of systems with state and input delays

Sufficient conditions are presented for a system with input delays having finite ℒ2-gain. The bounded real lemma conditions are infeasible when the actual and the delayed values of the input act on the system simultaneously. Considering the actual and delayed inputs as two independent inputs is shown to lead to very high upper-bound of the true ℒ2-gain. Several approaches are presented involving a scaling method which is based on upper-bounds of the delayed signal norms; a method which transforms the input delays to state delays with the help of introducing additional dynamics; and a method based on integral quadratic constraints. Both time-invariant and time-varying delays are considered. The methods are evaluated on an example of interconnected vehicles.

Lyapunov-Krasovskii functionals for evaluating H ∞ performance of platoons of communicating vehicles

A time-domain analysis of robust string stability is carried out for finite length vehicular platoons, where disturbances and constant delays in the inter-vehicle communication are present. The goal of the paper is to compare and evaluate the accuracy and computational cost of several Lyapunov-Krasovskii functional (LKF)-based methods. The proposed approach can be extended to cope with time-varying delays, large scale systems, vehicle model uncertainties and platoon heterogeneity. Simple delay-independent, delay-dependent and discretized complete LKF-based performance criteria are presented and demonstrated on a platoon with predecessor and leader following control architecture.