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.