Location: Chemistry ResearchTitle: Two closely related members of Arabidopsis 13-LOXs, LOX3 and LOX4, reveal distinct functions in response to plantparasitic nematode infection Author
Submitted to: Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2013
Publication Date: 5/28/2014
Citation: Ozalvo, R., Cabrera, J., Escobar, C., Christensen, S.A., Borrego, E.J., Kolomiets, M.V., Castresana, C., Iberkleid, I., Horowitz, S.B. 2014. Two closely related members of Arabidopsis 13-LOXs, LOX3 and LOX4, reveal distinct functions in response to plantparasitic nematode infection. Molecular Plant Pathology. 15(4):319-332. Interpretive Summary: Scientists from the USDA-ARS Center for Medical, Agricultural, and Veterinary Entomology in Gainesville, Florida, in collaboration with the Volcani Center in Bet Dagan, Israel and Texas A&M University, have characterized two closely related Arabidopsis lipoxygenase (LOX) genes, LOX3 and LOX4, in response to attack by root-knot nematode (Meloidogyne javanica) and cyst nematode (Heterodera schachtii). In tissue localization studies, LOX3 was locally expressed when second-stage juveniles reached the vascular bundle and during early stages of plant–nematode interaction through gall formation. LOX4 was also activated by nematode infection, although the signal weakened as infection and disease progressed. The generation of insertion mutants showed that LOX3 and LOX4 have distinct functions, in that lox3 mutants were more resistant than wild-type plants, but lox4 mutants were significantly more susceptible. Interestingly, the susceptibility of lox4 was accompanied by increased expression of some common defense metabolites, including increases in the jasmonic acid precursor 12-oxo-phytodienoic acid. Collectively, the results of this study indicate that LOX3 and LOX4 have distinct metabolic and signaling functions in response to nematode infection. Importantly, we show that LOX4 plays a key role in controlling defense against these parasitic plant-pathogens.
Technical Abstract: The responses of two closely related members of Arabidopsis 13-lipoxygenase (13-LOX), LOX3 and LOX4, to infection by the sedentary nematodes root-knot nematode (Meloidogyne javanica) and cyst nematode (Heterodera schachtii) were analyzed in transgenic Arabidopsis seedlings. Tissue localization of LOX3 and LOX4 gene expression using ß-glucuronidase (GUS) reporter gene constructs showed local induction of LOX3 expression when second-stage juveniles reached the vascular bundle and during early stages of plant–nematode interaction through gall and syncitia formation. Thin sections of nematode-infested knots indicated LOX3 expression in mature giant cells, and high expression in bordering dividing cells and those surrounding the female body. LOX4 promoter was also activated by nematode infection, although GUS signal weakened as infection and disease progressed. Homozygous insertion mutants lacking LOX3 were less susceptible than wild-type plants to root-knot nematode infection, as reflected by a decrease in female counts. Conversely, deficiency in LOX4 function led to a marked increase in females and egg masses. Susceptibility of lox4 was accompanied by increased expression of allene oxide synthase, allene oxide cyclase, ethylene-responsive transcription factor 4, and accumulation of the jasmonate precursor 12- oxo-phytodienoic acid. This response was not found in lox3 mutants. Taken together, our results reveal that LOX4 and LOX3 interfere differentially with distinct metabolic and signaling pathways and that LOX4 plays a major role in controlling plant defense against nematode infection.