Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/1999
Publication Date: N/A
Interpretive Summary: Carcinogenic aflatoxin is produced by Aspergillus infection of certain crops, such as corn, peanut, and cottonseed. Considerable effort is expended by the U.S. food industry to reduce aflatoxin to low levels. Previous work has shown that a product of a plant enzyme, lipoxygenase, affords some protection from aflatoxin production by Aspergillus. For this reason, the gene for peanut lipoxygenase was cloned and its sequence determined. The cloned enzyme was further characterized. Interestingly, Aspergillus infection of peanuts caused an increase in the amount of lipoxygenase produced. This work would be of interest to other scientists working on aflatoxin control in crops.
Technical Abstract: Several lines of evidence have indicated that lipoxygenase enzymes (LOX) and their products, especially 9S and 13S- hydroperoxy fatty acids, could play a role in the Aspergillus/seed interaction. Both hydroperoxides exhibit sporogenic effects on Aspergillus spp. [Calvo, A.M. and Keller, N.P.:Phytopathology 87:S14, 1997] and differentially modulate aflatoxin pathway gene transcription [Burow, G.B., Nesbitt T.C. and Dunlap, J.:Mol. Plant Microbe Interact. 10:380-387, 1997]. To examine the role of seed LOXs at the molecular level, a peanut seed gene, PnLOX1, was cloned and characterized. Analysis of nucleotide sequence suggest that PnLOX1 encodes a predicted 98 kD protein most similar in sequence and biochemical properties to soybean LOX2. The full length PnLOX1 cDNA was subcloned into an expression vector to determine the type(s) of hydroperoxide products the gene produces. Analysis of the oxidation products of PnLOX1 revealed that it produced a mixture of 9S-HPODE (9S- hydroperoxy-1OE, 12Z-octadecadienoic acid) and 13S-HPODE (13S- hydroperoxy-9Z, 11E-octadecadienoic acid). PnLOX1 is an organ specific gene which is constitutively expressed in immature cotyledons but is highly induced by methyl jasmonate, wounding and Aspergillus infections in mature cotyledons. Induction of PnLOX1 expression in Aspergillus-infected seeds may bear significant implications as to why peanut is highly susceptible to Aspergillus infection and subsequent aflatoxin contamination.