Plant Lipoxygenases. Physiological and Molecular Features

Abstract

The LOX pathway. The dioxygenation of long chain fatty acids such as α-linolenic acid (18:3), catalyzed by 9- and 13-LOXs, results in derivatives with several known or proposed functions in the plant cell (Table I). 9-HPOT, (10E,12Z)-9-Hydroperoxy-10,12,15-octadecatrienoic acid; 9-KOT, (10E, 12Z)-9-keto-10,12,15 octadecatrienoic acid; 13-HPOT, (10E,12Z)-13-hydroperoxy-10,12,15-octadecatrienoic acid; 13-KOT, (10E, 12Z)-13-keto-10,12,15-octadecatrienoic acid; 12-oxo-PDA, 12-oxo-10,15-phytodienoic acid. Products of LOX metabolism with a known or proposed activity Known activity. Proposed activity. Products of LOX metabolism with a known or proposed activity Known activity. Proposed activity. LOXs have active roles in several processes during plant life. PUFAs, Polyunsaturated fatty acids. LOX gene expression is regulated by different effectors such as the source/sink status (Fischer et al., 1999), JA (Creelman and Mullet, 1997), abscisic acid (Melan et al., 1993), and also by different forms of stress, such as wounding (Porta et al., 1999), water deficiency (Porta et al., 1999), or pathogen attack (Melan et al., 1993). In addition, LOX genes isolated from different plant species show differential organ-specific expression (Griffiths et al., 1999;Kolomiets et al., 2001; TableII). Plant LOX genes in different species: regiospecificity and subcellular localization of corresponding LOXs, and expression patterns of their mRNAs As archived in GenBank; please consult these accession nos. for more details about the pertinent authors. Activity determined from a cDNA expressed in Escherichia coli. Abbreviations: ABA, abscisic acid; BTH, benzo(1,2,3)thiadiazole-7-carbothioic acid; E, elicitor; Et, ethylene; F, fruit; Fl, flower; In, inflorecen; G, germination; INA, 2,6-dichlorolsonicotinic acid; J, jasmonates; L, leaf; N, nodule; P, pathogen; Po, pod; R, root; S, seed; St, stem; Sy, systemin; T, tuber; VSP, vegetative storate protein; W, wounding; Ws, water stress; and S, seed. Chloroplastic. Lipid bodies. Cytosolic. Vacuolar LOX. Plant LOX genes in different species: regiospecificity and subcellular localization of corresponding LOXs, and expression patterns of their mRNAs As archived in GenBank; please consult these accession nos. for more details about the pertinent authors. Activity determined from a cDNA expressed in Escherichia coli. Abbreviations: ABA, abscisic acid; BTH, benzo(1,2,3)thiadiazole-7-carbothioic acid; E, elicitor; Et, ethylene; F, fruit; Fl, flower; In, inflorecen; G, germination; INA, 2,6-dichlorolsonicotinic acid; J, jasmonates; L, leaf; N, nodule; P, pathogen; Po, pod; R, root; S, seed; St, stem; Sy, systemin; T, tuber; VSP, vegetative storate protein; W, wounding; Ws, water stress; and S, seed. Chloroplastic. Lipid bodies. Cytosolic. Vacuolar LOX. In recent years, our knowledge of the function of LOX and oxylipins in plants has increased with the contributions of many research groups. In addition, a number of plant LOX sequences are now available, making possible the analysis of their phylogenetic relationships and the elucidation of the connections between both LOX sequences and structures and their regiospecificity and activity. The objective of this review is to discuss recent advances on the role of LOXs in the physiology of plants. LOXs are normally present in the seeds of plants (Siedow, 1991). Nevertheless, LOXs do not have a clear physiological role in seed development, as indicated by the fact that in a soybean line lacking the three seed LOX isozymes, no adverse effects on crop performance were detected when compared with a normal line (Wang et al., 1999). This supports the idea that seed LOXs may function as storage proteins (Siedow, 1991). In peanuts (Arachis hypogaea), the gene coding for PnLOX1 is induced in mature seeds infected with Aspergillusspp. (Burow et al., 2000). The products of reactions catalyzed by PnLOX1, namely (13S)-hydro-peroxy-(9Z,11E)-octadecadienoic (13-HPOD) and (9S)-hydroperoxy-(10E, 12Z)-octadecadienoic acid (9-HPOD), are inhibitor and inducer, respectively, of mycotoxin synthesis, conferring a role in plant-fungus interaction to this particular LOX (Burow et al., 2000). During germination new LOXs are synthesized in the seedling and the cotyledons. Maximal accumulation of LOX protein and the corresponding mRNAs lasts from a few hours to a few days after germination. The LOX mRNAs synthesized during germination could also be found in the mature plant. Their levels were increased by the application of abscisic acid and JA, or by stresses such as wounding, pathogen infection, or water deficit (Melan et al., 1994; Park et al., 1994;Porta et al., 1999). Proposed model of the compartmentalization of LOXs and other enzymes of the oxylipins pathway. Chloroplastic 13-LOX produces 13-HPOT for the synthesis of JA through the action of AOS, which is localized in the inner envelope membrane (IM) of the chloroplast, and probably also for the synthesis of other defense relat