Alain Clérivet

Inoculation of Platanus acerifolia with Ceratocystis fimbriata f. sp. platani induces scopoletin and umbelliferone accumulation

Abstract Umbelliferone and scopoletin were induced in stem of Platanus acerifolia seedlings in response to inoculation with Ceratocystis fimbriata f. sp. platani, the canker stain disease agent. These phenolic compounds were found to be antifungal using bioassays and they therefore can be considered as phytoalexins. Nevertheless, they accumulate too late to totally inhibit conidial germination, thus allowing the parasite to colonize the tissues near the inoculation site.

Tyloses and gels associated with cellulose accumulation in vessels are responses of plane tree seedlings (Platanus × acerifolia) to the vascular fungus Ceratocystis fimbriata f. sp. platani.

Stems of plane tree seedlings were cytologically investigated regarding the involvement of tyloses and gels in defense reactions to Ceratocystis fimbriata f. sp platani, the canker stain disease agent. In the lumen of infected xylem vessels, cytochemical tests revealed the occurrence of compounds labeled for cellulose and which seem to be involved in gel formation. Immunogold methods indicated that pectin-rich material accumulated in the paramural area of vessel-associated parenchyma cells and around tylosis walls. Tylosis formation and deposition of pectin-containing gels were associated with metabolic changes of vessel-associated parenchyma cells. It is suggested that parenchyma cells play a key role in the defense of plane tree seedlings through plugging of xylem vessels leading to compartmentalization of the vascular fungus.

Accumulation of phytoalexins in leaves of plane tree (Platanus spp.) expressing susceptibility or resistance toCeratocystis fimbriata f. sp.platani

Inoculation of leaves of resistantPlatanus occidentalis and susceptiblePlatanus acerifolia leaves withCeratocystis fimbriata f. sp.platani, the canker stain disease agent, induced foliar necrosis and biosynthesis of two phytoalexins, scopoletin and umbelliferone. Foliar symptoms keep localized and accumulation of coumarin phytoalexins was rapid for incompatible interactions. Necrosis spread widely and accumulation of these phenolic compounds was much later and lower for compatible interactions. The differential response could be used in a genetic improvement program for resistance against canker stain.

Characterization of a new densovirus infecting the green peach aphid Myzus persicae

A new icosahedral DNA virus was isolated from aphids (Myzus persicae) that showed abnormal growth and development. The purified virus particles have a diameter of 20 nm and contain a single-stranded DNA molecule of approximately 5.7 kb. The viral particles are composed of five structural proteins (92, 85, 68, 64, and 57 kDa). As the main biophysical properties of this virus are similar to those of the members of the genus Densovirus it was tentatively named Myzus persicae densovirus (MpDNV). A PCR-based detection method and a polyclonal antiserum raised against MpDNV allowed the detection of the virus in a single-infected aphid. MpDNV is immunologically related to Junonia coenia densovirus, but not to other members of the subfamily Densovirinae. Biological assays showed that MpDNV could be both transmitted transovarially and horizontally via honeydew and saliva. MpDNV was able to infect whiteflies but not other aphid species tested.

A novel patatin-like protein from cotton plant, GhPat1, is co-expressed with GhLox1 during Xanthomonas campestris-mediated hypersensitive cell death

In cotton plant, Xanthomonas-induced hypersensitive response (HR) is accompanied by a lipid peroxidation process involving a 9-lipoxygenase (LOX), GhLox1. Initiation of this oxidative metabolism implies the release of the LOX substrates, or polyunsaturated fatty acids. Since patatin-like proteins (PLPs) are likely candidates for mediating the latter step, we searched for genes encoding such enzymes, identified and cloned one of them that we named GhPat1. Biochemical and molecular studies showed that GhPat1 expression was up-regulated during the incompatible interaction, prior to the onset of the corresponding galactolipase activity and cell death symptoms in tissues. Protein sequence analysis and modelling also revealed that GhPat1 catalytic amino acids and fold were conserved across plant PLPs. Based on these results and our previous work (Jalloul et al. in Plant J 32:1–12, 2002), a role for GhPat1, in synergy with GhLox1, during HR-specific lipid peroxidation is discussed.

A glycoprotein from Ceratocystis fimbriata f. sp. platani triggers phytoalexin synthesis in Platanus × acerifolia cell-suspension cultures

Abstract Treatment of cell-suspension cultures of Plantanus × acerifolia with a crude elicitor preparation from Ceratocystis fimbriata f. sp. plantani germlings induced the synthesis of the hydroxycoumarin phytoalexins, scopoletin and umbelliferone, and their accumulation in the growth medium. Only the protein-containing fraction of the culture filtrate was involved in cell response. By ultrafiltration of this last fraction, a major eliciting glycoprotein able to induce 80% coumarin synthesis was isolated. The glycoprotein was substituted by N-glycan(s) containing terminally linked mannose as revealed by lectin immunoblotting. The molecular mass of the eliciting compound is 66 kD (SDS-PAGE) and the native conformation was necessary for elicitor recognition by plane tree cells and thereby phytoalexin synthesis. We discuss the possible involvement of the GP 66 elicitor from the canker stain agent of the plane tree in the activation of the phenolic metabolism of the plant.

Can plants use an entomopathogenic virus as a defense against herbivores

It is by now well established that plants use various strategies to defend themselves against herbivores. Besides conventional weapons such as spines and stinging hairs and sophisticated chemical defenses, plants can also involve the enemies of the herbivores in their defense. It has been suggested that plants could even use entomopathogens as part of their defense strategies. In this paper, we show that Brassica oleraceae plants that are attacked by Myzus persicae aphids infected with an entomopathogenic parvovirus (M. persicae densovirus) transport the virus through the phloem locally and systematically. Moreover, healthy aphids that fed on the same leaf, but separated from infected aphids were infected via the plant. Hence, this is proof of the principle that plants can be vectors of an insect virus and can possibly use this virus as a defense against herbivores.

Effects of jasmonic acid and of an elicitor from Ceratocystis fimbriata f. sp. platani on the accumulation of phytoalexins in leaves of susceptible and resistant plane trees

Jasmonic acid and a glycoprotein elicitor produced by Ceratocystis fimbriata f. sp. platani, the canker stain agent, were tested for induction of coumarin phytoalexin accumulation in detached leaves of resistant (Platanus occidentalis) and susceptible plane trees (Platanus acerifolia and P. occidentalis). It was shown that leaves responded by different levels of phytoalexin accumulation after fungal elicitor treatment. The phytoalexins were excreted from elicited leaf tissues and accumulated in elicitor-containing droplets on the leaf surface. The highest level was found in leaves of resistant tree. Furthermore, pretreatment of leaves by jasmonic acid, sprayed before elicitor application, induced a further enhancement in phytoalexin accumulation which was higher in leaves of susceptible trees without any change in the ratio of the three phytoalexins, scopoletin, umbelliferone and xanthoarnol. However, jasmonic acid did not mimic biotic stress by itself. It only increased the response of leaf cells to fungal elicitor leading to an activation of coumarin metabolism.

Elicitation of Platanus×acerifolia cell-suspension cultures induces the synthesis of xanthoarnol, a dihydrofuranocoumarin phytoalexin

Abstract The treatment of cell-suspension cultures of Platanus×acerifolia with the GP66 elicitor produced by Ceratocystis fimbriata f. sp platani germlings triggers the fast and intense synthesis of a secondary metabolite whose 1 H NMR and 13 C NMR analysis led to the identification of xanthoarnol. This dihydrofuranocoumarin is principally accumulated in the growth medium reaching the maximum level 48 h after elicitor addition. Xanthoarnol was the major compound produced by elicited cells and showed an inhibitory effect on the germination of conidia of the parasitic fungus. Xanthoarnol is a new phytoalexin described in a plant–fungus interaction.

Les composés phénoliques et la résistance des plantes aux agents pathogènes

Summary Plant defense responses against microorganisms require many mechanisms as constitutive phenolic compounds and phytoalexins. These secondary metabolic products can be accumulated and involved in plant defence. Their activity was related to antimicrobial properties, involvement in cell wall reinforcement, modulation and induction of plant responses. Clonage of most genes coding for enzymes of phenolic metabolism give many means for genetic manipulations aiming to improve the effectiveness of plant defences. Recent results were very interesting but do not yet allow to define the real level of the involvement of phenolic compounds in plant disease resistance.