Alain Poupet

Pathogen-Induced Elicitin Production in Transgenic Tobacco Generates a Hypersensitive Response and Nonspecific Disease Resistance

The rapid and effective activation of disease resistance responses is essential for plant defense against pathogen attack. These responses are initiated when pathogen-derived molecules (elicitors) are recognized by the host. We have developed a strategy for creating novel disease resistance traits whereby transgenic plants respond to infection by a virulent pathogen with the production of an elicitor. To this end, we generated transgenic tobacco plants harboring a fusion between the pathogen-inducible tobacco hsr203J gene promoter and a Phytophthora cryptogea gene encoding the highly active elicitor cryptogein. Under noninduced conditions, the transgene was silent, and no cryptogein could be detected in the transgenic plants. In contrast, infection by the virulent fungus P. parasitica var nicotianae stimulated cryptogein production that coincided with the fast induction of several defense genes at and around the infection sites. Induced elicitor production resulted in a localized necrosis that resembled a P. cryptogea–induced hypersensitive response and that restricted further growth of the pathogen. The transgenic plants displayed enhanced resistance to fungal pathogens that were unrelated to Phytophthora species, such as Thielaviopsis basicola, Erysiphe cichoracearum, and Botrytis cinerea. Thus, broad-spectrum disease resistance of a plant can be generated without the constitutive synthesis of a transgene product.

RNase activity prevents the growth of a fungal pathogen in tobacco leaves and increases upon induction of systemic acquired resistance with elicitin.

The hypersensitive response and systemic acquired resistance (SAR) can be induced in tobacco (Nicotiana tabacum L.) plants by cryptogein, an elicitin secreted by Phytophthora cryptogea. Stem application of cryptogein leads to the establishment of acquired resistance to subsequent leaf infection with Phytophthora parasitica var nicotianae, the agent of the tobacco black shank disease. We have studied early events that occur after the infection and show here that a tobacco gene encoding the extracellular S-like RNase NE is expressed in response to inoculation with the pathogenic fungus. Upon induction of SAR with cryptogein, the accumulation of NE transcripts coincided with a rapid induction of RNase activity and with the increase in the activity of at least two different extracellular RNases. Moreover, exogenous application of RNase activity in the extracellular space of leaves led to a reduction of the fungus development by up to 90%, independently of any cryptogein treatment and in the absence of apparent necrosis. These results indicate that the up-regulation of apoplastic RNase activity after inoculation could contribute to the control of fungal invasion in plants induced to SAR with cryptogein.

Dianthramides A and B, two N-benzoylanthranilic acid derivatives from elicited tissues of Dianthus caryophyllus

Abstract Two new phenolic derivatives, dianthramide A and B, were isolated from Dianthus caryophyllus tissues elicited with mycelial extracts of Phytophthora parasitica . The purified substances were identified on the basis of their spectral data and were characterized as N -salicyl-4-methoxyanthranilic acid (dianthramide A) and N -salicyl-4-hydroxyanthranilic acid methyl ester (dianthramide B). Dianthramides A and B co-occur in carnation tissues with the known phytoalexin dianthalexin.

Separation and quantification of basic hydroxycinnamic amides and hydroxycinnamic acids by reversed-phase high-performance liquid chromatography

Abstract A method for the separation of basic hydroxycinnamic amides and hydroxycinnamic acids by high-performance liquid chromatography is described. N-p-Coumaryl-, N-caffeyl- and N-ferulylpetrescine, N-p-coumryl-, N-caffeyl- and N-ferulylspermidine and p-coumaric, caffeic, ferulic and sinapic acids were chromatographed on a μBondapak C18 reversed-phase column (particle size 9 μm) with different methanol—water gradients as the mobile phase. It is possible with this high-resolution and reproducible method to assay biological samples containing mre that 10−5 M of hydroxycinnamic amides, using either p-coumaric or ferulic acid as the internal standard: this is demonstrated for tobacco extracts.

Calcium Nutrition, Calmodulin Content and Susceptibility to TMV in Tobacco (Nicotiana Tabacum L. C.V. Xanthi)

Studying the influence of plant nutrition on the development of parasites in host plants is of great interest especially from an agronomic viewpoint. There are many reports that mineral deficiences affect plant susceptibility to viruses (Chessin and Scott, 1955; Seaker et al., 1982), but interpretations have been seldom proposed. In this view our choice of calcium nutrition has been made because of the recognized importance of calcium in the structure of membrane and cell wall where the primary interactions between the virus and the host cell do occur. Furthermore, the role of calcium as second messenger in many metabolic events is now accepted (Marme and Dieter, 1983), and it would be interesting to investigate it in a virus infected cell host model. So we propose to study the susceptibility to TMV (tobacco mosaic virus) of tobacco plants (Nicotiana tabacum L. c.v. Xanthi) in relation with their calcium nutrition and their calmodulin content.