Accumulation Of Hydroxyproline-rich Glycoproteins Research Articles

Cytosine-rich RNAs from infected melon plants and their in vitro translation products

Plant cell wall hydroxyproline-rich glycoproteins (HRGPs) are synthesized from cytosine-rich messenger RNA. As an approach to understanding the increased synthesis of HRGP in melon plants infected by Colletotrichum lagmarium, polyadenylated [poly(A)]RNA was isolated and subsequently enriched in cytosine-rich RNA by chromatography on oligoguanylic acid-cellulose [oligo(dG)cellulose]. In vitro translation of poly(A)RNA extracted from melon plants revealed several modifications of the peptide pattern during infection. In particular, the cytosine-rich RNA obtained coded for proline-rich peptides; among them, two peptides of molecular weight 54 500 and 56 000, were specifically coded by the cytosine-rich RNA of infected plants. The two peptides were characterized by a molecular weight similar to the peptide moiety of melon HRGP (55 000), and the time-course of their appearance in vitro was coincident with the in vivo accumulation of HRGP. The data strongly suggest that the two peptides are two HRGP precursors whose synthesis is increased as a result of an increase of translatable cytosine-rich RNA during infection.

Hydroxyproline-rich glycoprotein accumulation in the cell walls of plants infected by various pathogens

Twenty-five samples of tissue from 16 different host—pathogen systems were analysed for changes in the hydroxyproline (Hyp) content of their cell walls and for the glycosylation pattern of the Hyp. Hydroxyproline and the corresponding Hyp-rich glycoproteins (HRGP) increased in all infected dicotyledons studied but the extent varied according to the host species. Fungal, bacteria! and viral infections triggered accumulation of the glycoprotein. This response occurred in relation to resistant as well as susceptible reactions. No significant increases were found in infected monocotyledons. This work confirmed that the cell wall HRGP of dicotyledons are very different from those of monocotyledons. A hitherto unreported Hyp-oligosaccharide was identified in the cell walls of melon, bean and cucumber.

Cell Surfaces in Plant-Microorganism Interactions

Enrichment of the cell wall in hydroxyproline-rich glycoprotein is involved in the defense of muskmelon (Cucumis melo) seedlings to Colletotrichum 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 l-trans-hydroxyproline. It appears that the increase in the wall 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.