Sensitivity and speed of induced defense of cabbage (Brassica oleracea L.): dynamics of BoLOX expression patterns during insect and pathogen attack

Abstract

The lipoxygenase pathway is involved in the early steps of plant responses to herbivorous insects and phytopathogens. Induced defenses in the crucifer Brassica oleracea have been well documented. Here, we have cloned a LIPOXYGENASE (LOX) from B. oleracea (BoLOX). The sequence reveals that the BoLOX protein has a transit peptide for chloroplast targeting, which is characteristic for class 2 LOXs involved in jasmonic acid (JA) biosynthesis which takes place in the chloroplast. Phylogenetic analysis shows that BoLOX is closely related to B. napus BnLOX2fl and Arabidopsis thaliana AtLOX2, which mediates JA biosynthesis. BoLOX also shares functional characteristics with AtLOX2; BoLOX is inducible by wounding, JA treatment, and herbivores such as caterpillars (Pieris rapae, P. brassicae, and Mamestra brassicae), spider mites (Tetranychus urticae), locusts (Schistocerca gregaria), and a bacterial pathogen (Pseudomonas syringae pv. tomato). Of these, Pieris spp. caterpillars also induce AtLOX2 and JA biosynthesis in Arabidopsis. However, the aphid Myzus persicae did not induce BoLOX, which agrees with previous reports that this aphid induces neither AtLOX2 nor JA biosynthesis in Arabidopsis. Quantitative expression analysis of temporal, spatial, and density-dependent BoLOX transcript levels through real-time quantitative polymerase chain reaction demonstrated that BoLOX is maximally expressed after feeding by only two first-instar caterpillars for 24 h. Systemic expression was approximately 10-fold lower than local expression for herbivore-induced responses. The good correlation of BoLOX transcript levels with reports in the literature on induced defenses of B. oleracea is discussed.