Molecular cloning and characterization of the gene encoding osmotin protein in Petunia hybrida

Abstract

A cDNA clone encoding osmotin, PhOSM, was isolated from a cDNA library constructed from petal protoplast cultures of Petunia hybrida. PhOSM cDNA was composed of an open reading frame corresponding to protein of 246 amino acids and had a calculated molecular weight of 26.7 kDa. Database comparisons of the PhOSM protein sequences revealed high identity (89%) with the tobacco osmotin and tobacco OLP (Osmotin-Like-Protein). The increased accumulation of PhOSM mRNA in petal protoplast cultures was completely inhibited by treatment with Dhp (3,4-dehydro- l-proline), which is a inhibitor of peptydyl proline hydroxylation in cell wall regeneration. RNA blot analyses revealed that PhOSM was expressed primarily in roots and slightly in the pistil, 3 days after flowering. PhOSM expression was strongly induced in leaves that were exposed to Penicillium funiculosum, Erwinia stewartii and Pseudomonas syringae but not to Aspergillus nidulans. Upon wounding, PhOSM transcripts were induced in the directly damaged leaf but not systemically. Moreover, PhOSM transcript levels increased in response to octadecanoid pathway intermediates and treatments with aspirin and salicylic acid. Our results indicate that PhOSM is developmentally regulated as well as involved in wound-stress signal transduction.