We previously reported that LePR cDNA isolated from a cDNA library prepared from shikonin-producing cells of Lithospermum erythrorhizon encodes pathogenesis-related 10 (PR10) protein [J. Plant Physiol. 155 (1999) 364]. Here, we report an analysis of changes in LePR1 gene expression in response to signal molecules in the plant defense response system. Pathogen infection with bacteria ( Erwinia stewartii and Pseudomonas syringae) and fungi ( Aspergillus nidulans and Penicillium funiculosum) strongly induced LePR1 transcripts in inoculated leaves and in systemically affected leaves. When leaves were mechanically wounded, LePR1 gene expression was also increased 12 h after wounding. To evaluate the involvement with various signal transduction mechanisms, global signal molecules were applied to the leaves. Salicylic acid and its analogues, aspirin and BTH, definitely induced transcription of the LePR1 gene. Following H 2O 2 application, LePR1 transcripts accumulated to high levels 18 h after treatment and in a concentration-dependent manner. LePR1 transcript levels were also increased in response to octadecanoid pathway intermediates and to treatments with ABA. Our results indicate that the LePR1 gene shows very extensive and sensitive responses to pathogen infection as well as defense-related signal molecules.