A peanut seed lipoxygenase responsive to Aspergillus colonization

Several lines of evidence have indicated that lipoxygenase enzymes (LOX) an d their products, especially 9S- and 13S-hydroperoxy fatty acids, could pla y a role in the Aspergillus/seed interaction. Both hydroperoxides exhibit s porogenic effects on Aspergillus spp. (Calvo, A., Hinze, L., Gardner, H.W. and Keller, N.P. 1999. Appl. Environ. Microbiol. 65: 3668-3673) and differe ntially modulate aflatoxin pathway gene transcription (Burow, G.B., Nesbitt , T.C., Dunlap, J. and Keller, N.P. 1997. Mol. Plant-Microbe Interact. 10: 380-387). To examine the role of seed LOXs at the molecular level, a peanut (Arachis hypogaea L.) seed gene, PnLOX1, was cloned and characterized. Ana lysis of nucleotide sequence suggests that PnLOX1 encodes a predicted 98 kD a protein highly similar in sequence and biochemical properties to soybean LOX2. The full-length PnLOX1 cDNA was subcloned into an expression vector t o determine the type(s) of hydroperoxide products the enzyme produces. Anal ysis of the oxidation products of PnLOX1 revealed that it produced a mixtur e of 30% 9S-HPODE (9S-hydroperoxy-10E, 12Z-octadecadienoic acid) and 70% 13 S-HPODE (13S-hydroperoxy-9Z, 11E-octadecadienoic acid) at pH 7. PnLOX1 is a n organ-specific gene which is constitutively expressed in immature cotyled ons but is highly induced by methyl jasmonate, wounding and Aspergillus inf ections in mature cotyledons. Examination of HPODE production in infected c otyledons suggests PnLOX1 expression may lead to an increase in 9S-HPODE in the seed.