No abstract

Constitutive overexpression of a protein involved in plant defense mechanisms to disease is one of the strategies proposed to increase plant tolerance to fungal pathogens. A hybrid endochitinase gene under a constitutive promoter was introduced by Agrobacterium-mediated transformation into a winter-type oilseed rape (Brassica napus var. oleifera) inbred line. Progeny from transformed plants was challenged using three different fungal pathogens (Cylindrosporium concentricum, Phoma lingam, Sclerotinia sclerotiorum) in field trials at two different geographical locations. These plants exhibited an increased tolerance to disease as compared with the nontransgenic parental plants.

No abstract

Enrichment of the cell wal in hydroxyproline-rich glycoprotein is involved in the defense of muskmelon (Cucumis melo) seedings to CoUetotriclwm lagenarium, the causative agent of anthracnose. The extent to which this accumulation proceeds may be experimentally modified by treating plants with ethylene or growing them in the presence of free Ltrans-hydroxyproline. It appears that the increase in the wail hydroxyproline-rich glycoprotein mediated through ethylene is paralleled by an increasing resistance of the host to the pathogen. Inversely, inhibiting the synthesis of this glycoprotein in diseased plants is strictly correlated to an accelerated and more intense colonization of the host by the pathogen.In both cases, the inverse relationship between the accumulation of hydroxyproline-rich glycoproteins and the ability of the pathogen to develop in the host has been checked by the quantification, in infected tissues, of glucosamine, a characteristic component of chitin-containing fungi.It has been shown that hydroxyproline is associated with the cell wall of green plants (23)(24)(25). Its level varies somewhat, depending on the plant or organ considered (6, 28) but, with the exception of some organisms like Chlamydomonas (29), it is generally low. This level is markedly increased in a few instances where the integrity of the plant is disrupted by wounding, aeration of tissue slices (8), subculturing, and in melon plants infected by a fungal pathogen (16). The observed increase in diseased plants accounts for a cell wall enrichment of the glycosylated hydroxyprolyl and seryl residues (15) which typify the hydroxyprolinerich glycoprotein (HRGP)3 called "extensin" by Lamport (23).The question of the significance of this glycoprotein accumulation in diseased plants has been raised, particularly because cell surface glycoconjugates are often involved in cell to cell interactions (4, 10, 35) of which the host-pathogen system is a special case. This paper reports on the correlations between the level of HRGP in the cell wall, and the extent of pathogen spread in melon plants infected by Colletotrichum lagenarium. The approach to this problem consisted of modifying the hydroxyproline level 'This work received financial support from the Centre National de la Recherche Scientifique (L.A. n°241).