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A Novel Lipoxygenase in Pea Roots. Its Function in Wounding and Biotic Stress

Institute of Plant Protection, Bari Section, Consiglio Nazionale delle Ricerche, 70126 Bari, Italy (P.V., M.T.M., T.B.-Z.); Institute of Biology and Agricultural Biotechnology, Rome Section, Consiglio Nazionale delle Ricerche, 00016, Monterotondo, Rome, Italy (D.G.); Institute of Science of Food Production, Lecce Section, Consiglio Nazionale delle Ricerche, 73100 Lecce, Italy (A.L.); Dunn Human Nutrition Unit, Medical Research Council, Cambridge CB2 2XY, United Kingdom (A.R.); and Division of Environmental and Evolutionary Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom (M.W.K.)

The genome of pea (Pisum sativum) contains genes encoding a family of distinct lipoxygenases (LOX). Among these, LOXN2 showed eight exons encoding a 93.7-kD enzyme, harboring two C-terminal deletions and an unusual arginine/threonine-tyrosine motif in the domain considered to control the substrate specificity. LOXN2, when overexpressed in yeast, exhibited normal enzyme activity with an optimum at pH 4.5, and a dual positional specificity by releasing a 3:1 ratio of C-9 and C-13 oxidized products. The predicted LOXN2 structure lacked a loop present in soybean (Glycine max) LOX1, in a position consistent with control of the degree of substrate access to the catalytic site and for LOXN2's dual positional specificity. The LOXN2 gene was tightly conserved in the Progress 9 and MG103738 genotypes, respectively, susceptible and resistant to the root cyst nematode Heterodera goettingiana. LOXN2 transcription was monitored in roots after mechanical injury and during nematode infection. The message peaked at 3 and 24 h after wounding in both genotypes and was more abundant in the resistant than in the susceptible pea. In nematode-infected roots, transcription of several LOX genes was triggered except LOXN2, which was repressed in both genotypes. In situ hybridization revealed that LOXN2 message was widespread in the cortex and endodermis of healthy roots, but specifically localized at high level in the cells bordering the nematode-induced syncytia of infected roots. However, LOXN2 transcript signal was particularly intense in collapsing syncytia of MG103738 roots, suggesting LOXN2 involvement in late mechanisms of host resistance.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.106.081679.

^* Corresponding author; e-mail p.veronico{at}ba.ipp.cnr.it; fax: 39–080–558–0468.

Received April 7, 2006; returned for revision April 7, 2006; accepted April 26, 2006.

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