A role for 9-lipoxygenases in maize defense against insect herbivory

<p>Feeding by <i>Spodoptera exigua</i> (beet armyworm) larvae on <i>Zea mays</i> (maize) induces expression of 9-lipoxygenases to a greater extent than 13-lipoxygenases. Whereas 13-lipoxygenases have an established role in the synthesis of jasmonates that serve as defense signaling molecules in many plant species, relatively little is known about the role of 9-lipoxygenases in herbivore defense. Phylogenetic analysis of lipoxygenases from maize inbred lines B73 and W22 shows that, although most <i>Lox</i> genes are present in both lines, <i>Lox12</i>, a 9-lipoxygenase that has been implicated in fungal defense, is truncated and unlikely to encode a functional protein in W22. Two independent <i>Mutator</i> transposon insertions in another 9-lipoxygenase, <i>Lox4</i>, caused improved <i>S. exigua</i> growth on the mutant lines relative to wildtype W22. This observation suggests a function in herbivore defense for metabolic products downstream of maize Lox4, either through direct toxicity or a perhaps an as yet unknown signaling function.</p>