Over-expression of a pathogenesis-related protein gene in transgenic tomato alters the transcription patterns of other defence genes

A transgenic tomato (Lycopersicon esculentum Mill.) line that over-expressed the tobacco class 5 pathogenesis-related (PR) gene for osmotin, was tested for altered transcriptional regulation of other PR genes which could account for the increased resistance to pathogens observed in this PR5 gene transformant. Transcripts encoding PR proteins were constitutively expressed at low levels in seedling tissues of both transgenic and control plants. Expression was increased by exogenous treatment with benzo(1,2,3)thiodiazole-7-carbothioic acid S-methyl ester (BTH), suggesting enhanced pathogen resistance, but not by salicylic acid (SA). In the osmotin PR5-transgenic line, induction of PR1 gene transcripts by BTH was more intense than in the non-transformed control line, while the opposite was true for PR4 gene transcripts. In leaf tissues, SA-treatment induced expression of both PR1 and PR4 genes. As observed in seedlings, the increased transcription of PR genes in the leaves of the SA-treated transgenic line was more intense for PR1 gene(s) and less intense for PR4 gene(s), compared to the non-transformed control.