Potato Lipoxygenase POTLX-3 Gene is Expressed In Response to Pathogens but Not Wounding
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Lipoxygenases are the first committed enzymes in biosynthetic pathways that produce jasmonic acid, methyl jasmonate, traumatin, fatty acid hydroperoxides, and volatile aldehydes. These pathways often function in growth- and defense-related processes in plants. Products of lipoxygenases may be the primary cause of the hypersensitive response (HR) because lipoxygenase by-products such as organic free radicals and active oxygen species are involved in cell membrane degradation during resistance responses against pathogens. In order to study lipoxygenase involvement in defense responses against pathogens, we have isolated and characterized a potato lipoxygenase gene that we have designated POTLX-3. POTLX-3 is not expressed in any potato organs, is not induced by wounding, but is strongly induced in leaves treated with ethylene, methyl jasmonate, or inoculum of Phytophthora infestans, the causal agent of potato late blight. In response to infection, POTLX-3 transcripts accumulate more rapidly in resistant lines than in susceptible lines. In resistant lines, the greatest amount of induction preceded the visual appearance of localized necrotic lesions, consistent with possible involvement of POTLX-3 in HR development. Expression of POTLX-3 also is activated in response to inoculation with the bacterial pathogen Pseudomonas syringae pv. phaseolicola, which causes strongly expressed HR in all potato cultivars. Thus, POTLX-3 expression is not a specific response to P. infestans, but rather a common response related to HR development against a broad range of pathogens. Pattern of POTLX-3 expression indicates that it may have a specific role in defense mechanisms against pathogens.
