Lipoxygenase gene expression in the tobacco-Phytophthora parasitica nicotianae interaction

A recently isolated cDNA clone of tobacco (Nicotiana tabacum L.) lipoxygenase (LOX) was used to study LOX gene expression in tobacco cell-suspension cultures and intact plants in response to infection with Phytophthora parasitica nicotianae (Ppn). Southern blot analysis of tobacco DNA indicated that only a small number of LOX genes hybridize to this probe. These genes were not constitutively expressed to a detectable level in control cells and healthy plants. In contrast, a rapid and transient accumulation of transcripts occurred in cells and plants after treatment with elicitor and inoculation with zoospores of Ppn, respectively. In cell cultures LOX gene expression could also be induced by linolenic acid, a LOX substrate, and by methyl jasmonate, one of the products derived from the action of LOX on linolenic acid. In the infection assays, LOX gene expression and enzyme activity were observed earlier when the plants carried a resistance gene against the race of Ppn used for inoculation. The differential expression of LOX during the race-cultivar-specific interaction between tobacco and Ppn, as well as its regulation by elicitors and jasmonate, suggest a role of LOX in plant resistance and establishment of the defense status against this pathogen.