A gene encoding a novel isoform of the PR-1 protein family from tomato is induced upon viroid infection.

A Lycopersicon esculentum cDNA clone encoding an acidic-type pathogenesis-related protein (PR-1a1) was isolated, sequenced and characterized. It contains an open reading frame of 175 amino acids and the mature protein, after cleavage of the 21 amino acid signals peptide, has a pI of 5.24. The protein shows highest homology (75% identity) with the basic pathogenesis-related prb-1b protein from tobacco. The PR-1a1 gene shows constitutive expression in roots from tomato plants. It is expressed in leaves and stems upon viroid infection, and appears to be induced by ethylene. Comparative studies of this gene and a related basic isoform of PR-1 indicate that the expression of these two members of the PR-1 gene family in tomato may be differentially regulated upon viroid infection.