Location: Crop Genetics and Breeding ResearchTitle: Comparative molecular and biochemical characterization of segmentally duplicated 9-lipoxygenase genes ZmLOX4 and ZmLOX5 of maize Author
Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2010
Publication Date: 3/27/2010
Citation: Park, Y., Gobel, C., Ni, X., Feussner, I., Kolomiets, M.V. 2010. Comparative molecular and biochemical characterization of segmentally duplicated 9-lipoxygenase genes ZmLOX4 and ZmLOX5 of maize. Planta. 231:1425-1437. Interpretive Summary: Plant intracellular composition of lipids is frequently altered during plant development and in response to a variety of environmental stresses. This often results in the formation of a group of the oxidized fatty acids in plants. Initial oxidation products are generated by either auto-oxidation or by the enzymatic reactions of several oxidative enzymes including a group of lipid oxidation enzymes, also known as lipoxygenases. To date, despite a widely recognized biological significance of the oxidized fatty acids, precise physiological, molecular and biochemical function of diverse types of the lipid oxidation enzymes that catalyze this process is still not well understood in plants. In particular, the physiological roles of a subset of the lipid oxidation enzymes, that is, the 9-lipoxygenases, in grass development and stress adaptation have not been well understood in general. In this study we use corn plants to elucidate the physiological functions of this specific group of genes and their diverse metabolites in plant development and defenses against insect pests and diseases. We isolated and comprehensively characterized a closely-related pair of two 9-lipoxygenase genes. This study demonstrated that, although these two genes share more than 94% sequence identity, the two genes are differentially regulated and expressed in corn plant tissues and organs. The genes respond differently to the treatments by stress hormones, wounding, insect herbivory, and pathogen infection.
Technical Abstract: Lipoxygenases (LOX) catalyze hydroperoxidation of polyunsaturated fatty acids to form structurally and functionally diverse oxylipins. Precise physiological and biochemical functions of individual members of plant multigene LOX families are largely unknown. Herein we report on detailed molecular and biochemical characterization of two closely related maize 9-lipoxygenase paralogs, ZmLOX4 and ZmLOX5. Recombinant ZmLOX5 protein displayed clear 9-LOX regio-specificity at both neutral and slightly alkaline pH. The genes were differently expressed in various maize organs and tissues as well as in response to different stress treatments. The transcripts of ZmLOX4 accumulated predominantly in roots and shoot apical meristem, whereas ZmLOX5 was expressed in most tested aboveground organs. Although both genes were not expressed in untreated leaves, they displayed differential induction by defense-related hormones. While ZmLOX4 was only induced by jasmonic acid (JA), the transcripts of ZmLOX5 were increased in response to JA, abscisic acid (ABA) and salicylic acid (SA) treatments. ZmLOX5 was transiently induced in response to mechanical wounding and fall armyworm herbivory, suggesting a putative role for this gene in defenses against insects. Surprisingly, despite of JA- and wound-inducibility of ZmLOX4, the gene was not responsive to insect herbivory. These results suggest that the two genes may have distinct roles in maize adaptation to diverse biotic- and abiotic stress. Both paralogs were similarly induced by virulent and avirulent strains of the fungal leaf pathogen Cochliobolus carbonum. Putative physiological roles for the two genes are discussed in the context of their biochemical and molecular properties.