An ultraviolet B condition that affects growth and defense in Arabidopsis

Ultraviolet B light (UV-B, 280-315 nm) is the shortest wavelength of the solar spectrum reaching the surface of the Earth. It has profound effects on plants, ranging from growth regulation to severe metabolic changes. Low level UV-B mainly causes photomorphogenic effects while higher levels can induce stress, yet these effects tend to overlap. Here we identified a condition that allows growth reduction without obvious detrimental stress in wild type Arabidopsis rosette plants. This condition was used to study the effects of a daily UV-B dose on plant characteristics of UV-B adapted plants in detail. Exploration of the transcriptome of developing leaves indicated downregulation of genes involved in stomata formation by UV-B, while at the same time genes involved in photoprotective pigment biosynthesis were upregulated. These findings correspond with a decreased stomatal density and increased UV-B absorbing pigments. Gene ontology analysis revealed upregulation of defense related genes and meta-analysis showed substantial overlap of the UV-B regulated transcriptome with transcriptomes of salicylate and jasmonate treated as well as herbivore exposed plants. Feeding experiments showed that caterpillars of Spodoptera littoralis are directly affected by UV-B, while performance of the aphid Myzus persicae is diminished by a plant mediated process

GalNAc/Gal-Binding Rhizoctonia solani Agglutinin Has Antiproliferative Activity in Drosophila melanogaster S2 Cells via MAPK and JAK/STAT Signaling

Rhizoctonia solani agglutinin, further referred to as RSA, is a lectin isolated from the plant pathogenic fungus Rhizoctonia solani. Previously, we reported a high entomotoxic activity of RSA towards the cotton leafworm Spodoptera littoralis. To better understand the mechanism of action of RSA, Drosophila melanogaster Schneider S2 cells were treated with different concentrations of the lectin and FITC-labeled RSA binding was examined using confocal fluorescence microscopy. RSA has antiproliferative activity with a median effect concentration (EC50) of 0.35 µM. In addition, the lectin was typically bound to the cell surface but not internalized. In contrast, the N-acetylglucosamine-binding lectin WGA and the galactose-binding lectin PNA, which were both also inhibitory for S2 cell proliferation, were internalized whereas the mannose-binding lectin GNA did not show any activity on these cells, although it was internalized. Extracted DNA and nuclei from S2 cells treated with RSA were not different from untreated cells, confirming inhibition of proliferation without apoptosis. Pre-incubation of RSA with N-acetylgalactosamine clearly inhibited the antiproliferative activity by RSA in S2 cells, demonstrating the importance of carbohydrate binding. Similarly, the use of MEK and JAK inhibitors reduced the activity of RSA. Finally, RSA affinity chromatography of membrane proteins from S2 cells allowed the identification of several cell surface receptors involved in both signaling transduction pathways

Toxicity and mode of action of fungal lectins in pest insects important in agriculture

The urgent need for more and safer agricultural products, especially food, is rapidly increasing due to an increase of the global human population. Agriculture has suffered from multiple problems, a major threat being insects. These insects have been controlled with different methods mainly by using chemical insecticides. But many problems are associated with the use of these insecticides pushed entomologists to develop alternative methods for these chemical insecticides. Many plant lectins have been reported to possess insecticidal properties but very little is known about the entomotoxic effects of fungal lectins. The main objective of this PhD thesis is to study the insecticidal activity of fungal lectins isolated from two basidiomycetes namely Rhizoctonia solani and Sclerotinia sclerotiorum towards different pest insects and insect cell lines and to investigate the mode of action of these lectins. In vivo assays showed that these lectins have strong insecticidal activity towards pea aphid (Acyrthosiphon pisum) and cotton leafworm (Spodoptera littoralis). While in vitro assays using insect cell lines showed that the activity of these lectins depends on apoptosis induction or inhibition of cell proliferation. These findings suggest that fungal lectins are interesting tool that can be used for bioengineering insect resistance in important agronomical crops

Glycosylation signatures in Drosophila : fishing with lectins

Glycosylation is a co- and/or post-translational protein modification that generates enormous structural diversity among glycoproteins. In this study, immobilized lectins were used to capture glycoproteins with different glycan profiles from Drosophila melanogaster extracts. On the basis of previous results from glycan array analyses, the snowdrop (Galanthus nivalis) agglutinin (GNA), the tobacco (Nicotiana tabacum) lectin (Nictaba) and the Rhizoctoni solani agglutinin (RSA) were used to select for a broad range of N- and O-glycan structures. After different lectin affinity chromatographies, the glycoproteome of Drosophila was analyzed using LC-MS/MS and glycoprotein abundances were calculated by different label-free methods. Bioinformatics tools were used to annotate the identified glycoproteins and the glycoproteins were classified according to their molecular function or their involvement in a biological process. Subsequent enrichment analysis (using the DAVID database) was employed to find biological processes or molecular functions in Drosophila in which a particular glycan signature is overrepresented. The results presented here clearly demonstrate that next to the presence of high-mannose and paucimannose N-glycans, Drosophila is capable of synthesizing glycoproteins carrying extended hybrid and complex N-linked glycans. Furthermore, it was demonstrated that a specific glycosylation signature can be associated with a functionally related group of glycoproteins in Drosophila, both in terms of biological process and molecular function