Antisense-mediated depletion of a potato lipoxygenase reduces wound induction of proteinase inhibitors and increases weight gain of insect pests

De novo jasmonic acid (JA) synthesis is required for wound-induced expressi on of proteinase inhibitors and other defense genes in potato and tomato. T he first step in JA biosynthesis involves lipoxygenase (LOX) introducing mo lecular oxygen at the C-13 position of linolenic acid. We previously have s hown that, in potato, at least two gene families code for 13-LOX proteins. We have now produced transgenic potato plants devoid of one specific 13-LOX isoform (LOX-HS) through antisense-mediated depletion of its mRNA. LOX-H3 depletion largely abolishes accumulation of proteinase inhibitors on woundi ng, indicating that this specific LOX plays an instrumental role in the reg ulation of wound-induced gene expression. As a consequence, weight gain of Colorado potato beetles fed on antisense plants is significantly larger tha n those fed on wild-type plants. The poorer performance of LOX-H3-deficient plants toward herbivory is more evident with a polyphagous insect; larvae of beet armyworm reared on the antisense lines have up to 57% higher weight than those fed on nontransformed plants. LOX-H3 thus appears to regulate g ene activation in response to pest attack, and this inducible response is l ikely to be a major determinant for reducing performance of nonspecialized herbivores. However, the regulatory role of LOX-H3 is not caused by its inv olvement in the wound-induced increase of JA, as wild-type and LOX-H3 defic ient plants have similar jasmonate levels after wounding. LOX-H3-deficient plants have higher tuber yields. The apparent effect of suppressing the ind ucible defensive response on plant vigor suggests that it may pose a penalt y in plant fitness under nonstress situations.