Although thionins and 2s albumins are generally considered as storage proteins, both classes of seed proteins are known to inhibit the growth of pathogenic fungi. We have now found that the wheat (Trificum aesfivum 1.) or barley (Hordeum vu/gare 1.) thionin concentration required for 50% inhibition of fungal growth is lowered 2-to 73-fold when combined with 2s albumins (at sub-or noninhibitory concentrations) from radish (Raphanus sativus 1.) or oilseed rape (Brassica napus 1.). Furthermore, the thionin antifungal activity is synergistically enhanced (2-to 33-fold) by either the small subunit or the large subunit of the radish 2s albumins. Three other 2s albumin-like proteins, the barley trypsin inhibitor and two barley Bowman-Birk-type trypsin inhibitor isoforms, also act synergistically with the thionins (2-to 55-fold). The synergistic activity of thionins combined with 2s albumins is restricted to filamentous fungi and to some Cram-positive bacteria, whereas Cram-negative bacteria, yeast, cultured human cells, and erythrocytes do not show an increased sensitivity to thioninlalbumin combinations (relative to the sensitivity to the thionins alone). Scanning electron microscopy and measurement of K+ leakage from fungal hyphae revealed that 2s albumins have the same mode of action as thionins, namely the permeabilization of the hyphal plasmalemma. Moreover, 25 albumins and thionins act synergistically in their ability to permeabilize fungal membranes.
Plants are host to a large amount of pathogenic bacteria. Fire blight, caused by the bacterium Erwinia amylovora, is an important disease in Rosaceae. Pathogenicity of E. amylovora is greatly influenced by the production of exopolysaccharides, such as amylovoran, and the use of the type III secretion system, which enables bacteria to penetrate host tissue and cause disease. When infection takes place, plants have to rely on the ability of each cell to recognize the pathogen and the signals emanating from the infection site in order to generate several defence mechanisms. These mechanisms consist of physical barriers and the production of antimicrobial components, both in a preformed and an inducible manner. Inducible defence responses are activated upon the recognition of elicitor molecules by plant cell receptors, either derived from invading microorganisms or from pathogen-induced degradation of plant tissue. This recognition event triggers a signal transduction cascade, leading to a range of defence responses [reactive oxygen species (ROS), plant hormones, secondary metabolites, ...] and redeployment of cellular energy in a fast, efficient and multiresponsive manner, which prevents further pathogen ingress. This review highlights the research that has been performed during recent years regarding this specific plantpathogen interaction between Erwinia amylovora and Rosaceae, with a special emphasis on the pathogenicity and the infection strategy of E. amylovora and the possible defence mechanisms of the plant against this disease.
We have developed a simple protocol to allow the production of transgenic banana plants. Foreign genes were delivered into embryogenic suspension cells using accelerated particles coated with DNA. Bombardment parameters were optimized for a modified particle gun resulting in high levels of transient expression of the beta-glucuronidase gene in both banana and plantain cells. Bombarded banana cells were selected with hygromycin and regenerated into plants. Molecular and histochemical characterization of transformants revealed the stable integration of the transferred genes into the banana genome.
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