A leaf lipoxygenase of potato induced specifically by pathogen infection

Lipoxygenase (LOX) activity has been identified consistently during pathoge n-induced defense responses. Here we report the involvement of a specific l eaf LOX gene of potato (Solanum tuberosum), designated POTLX-3 (GenBank/EMB L accession no. U60202), in defense responses against pathogens. The sequen ce of POTLX-3 does not match any other LOX genes of potato and has the grea test match to a tobacco LOX gene that contributes to a resistance mechanism against Phytophthora parasitica var nicotianae. POTLX-3 transcript accumul ation was not detected in untreated, healthy potato organs or in wounded ma ture leaves. POTLX-3 mRNA accumulation was induced in potato leaves treated with ethylene or methyl jasmonate or infected with either virulent or avir ulent strains of Phytophthora infestans, the causal agent of late blight. D uring the resistance response, POTLX-3 was induced within 6 hours, increase d steadily through 24 hours, and its mRNA continued to accumulate for a wee k after inoculation. In contrast, when a plant was susceptible to P. infest ans, induction of mRNA accumulation in response to inoculation was inconsis tent and delayed. LOX activity assayed during an incompatible interaction i n leaves peaked 3 days earlier than during a compatible interaction. POTLX- S mRNA accumulation also was induced during hypersensitive response develop ment caused by the incompatible pathogen Pseudomonas syringae pv phaseolico la. Our results show that POTLX-3 may be involved specifically in defense r esponses against pathogen infection.