The role of annexins in defense response of Arabidopsis thaliana plants

Principal investigator: D. Konopka-Postupolska
Participants: M. Lichocka

Nowadays, a major challenge in stress researches is to explore the mechanisms of signaling transduction pathways that mediate interaction between organism and its environment. Over the years, search for "cellular language" has pointed out calcium ion and calcium binding proteins as ubiquitous messengers in the cell responses to the environmental and hormonal signals. Annexins are a family of calcium binding proteins that are expressed in almost all eukaryotic organisms and whose functions, despite 25 years of investigations, are still poorly understood. They are abundant proteins and their content in plant cell can be estimated as about 0.1% of total soluble proteins. It means that annexins can be considered as a very important modulator of time course and magnitude of calcium peak. They are multifunctional proteins, and may function not only on the very beginning of calcium signaling cascades but also can be a component of different signaling pathways. We focus our attention on AnnAt1 from A. thaliana plants and investigate its function in stress responses. We find that AnnAt1 mRNA accumulates in response to abiotic stressors that result in osmotic stress and after application of stress hormone, abscisic acid. Annexin 1 was shown to modulate in yet unknown way an oxidative burst in plant cells which is believed to be a common theme underlying the plant tolerance to various abiotic stresses and pathogen infection. Thus, we are also working on characterization of AnnAt1 function in infection. Besides, there are some indications that annexin 1 can function as an F-actin binding protein that anchors actin cytoskeleton to cellular membranes. To address this question we characterize actin cytoskeleton rearrangements after infection of plants that do not express AnnAt1 protein.


Mapping and characterization of a novel elements involved in resistance of potato (Solanum tuberosum L.) to pathogen infection and environmental stimuli

Principal investigator: J. Hennig
Participants: K. Woroniecka, M. Szalonek

Breeding of resistant potato cultivars is the most effective and environmentally safe strategy to achieve protection against potato viruses. The development of DNA markers linked to desired traits, including disease resistance genes, becomes more and more helpful for marker-assisted selection in potato breeding programs. We have developed simple and robust PCR-based approaches for detection a set of the alleles: Ry-fsto, Ns, Gm, Rm and PLRV.4 conferring resistance of potato to Potato virus Y (PVY), Potato virus S (PVS), Potato virus M (PVM) and Potato leafroll virus (PLRV), respectively.
In cultivar (cv.) Rywal, we revealed a novel gene Ny-1, for resistance to PVY infection. This is the first gene that confers hypersensitivity in potato plants both to common (PVY0) and necrotic (PVYN) strains of PVY. The Ny-1 gene mapped on the short arm of potato chromosome IX, where various resistance genes are clustered in Solanaceous genomes. HR in cv. Rywal is temperature-dependent. Strains of PVY0 and PVYN including subgroup PVYNTN, are effectively localized at the site of infection when plants are grown at 20C. In contrast, at elevated temperature (28C) plants are systemically infected. In order to elucidate the role of salicylic acid (SA) for defense responses in potato, we analyzed transgenic cv. Rywal plants expressing the nahG gene (coding for salicylate hydroxylase) for alterations in their response to infection with PVY. We found that inhibition of PVY spreading at 20C is salicylic acid-dependent, suggesting that SA is an important element in defense response of potato plants.
In field trials, PVY was restricted only to the inoculated leaves and PVY-free tubers were produced in potato carrying Ny-1 gene. Therefore, the gene Ny-1 can be useful for potato breeding as an alternative donor of PVY resistance, since it is efficacious in practice like resistance conferred by Ry genes.
Project has been performed in collaboration with Plant Breeding and Acclimatization Institute in Mochw.


Phytopathological and phenotypic analysis of plants modified in protein phosphorylation pattern

Principal investigator: M. Krzymowska
Participants: J. Hennig, R. Hoser

MAPK cascades control various aspects of plant growth and development. They are also involved in stress responses, including pathogen attack. Rapid activation of the tobacco mitogen-activated protein kinase, SIPK (Salicylic Acid Induced Protein Kinase), and its orthologs from other plant species following infection has been associated with the induction of multiple components of the defense responses. Although SIPK has been identified a decade ago, a consistent model depicting its involvement in resistance response is still lacking. We apply several approaches in order to elucidate physiological role of SIPK, including identification of its phosphorylation targets. Additionally, our preliminary data suggest SIPK could be also a negative regulator of growth and developmental processes.


Comparative secretome analysis of various pathovars of Pseudomonas syringae

Principal investigator: M. Krzymowska
Participants: F. Giska, M. Piechocki

Plant pathogenic bacteria produce about 50 various virulence factors. These proteins are injected by type three secretion system either into apoplast or into host cells. They could be involved in nutrient acquisition, optimizing plant cell metabolism for bacterial growth and inhibiting/modulating host defense response. Some of these virulence factors are recognized by plant surveillance system (in such situations these factors are referred to as avirulence factors, avr) probably by changes (disturbances) in plant cell homeostasis evoked by the avr factors. In this project, we set up a procedure to isolate and identify proteins secreted by Pseudomonas syringae pv. tabaci. Our experiments revealed 17 effectors of this strain. Sequences encoding seven of them were cloned into vectors enabling their expression in prokaryotic and eukaryotic systems to further characterize them.