Oxylipin channelling in Nicotiana attenuata: lipoxygenase 2 supplies substrates for green leaf volatile production.

Lipoxygenases (LOXs) are key enzymes in the biosynthesis of oxylipins, and catalyse the formation of fatty acid hydroperoxides (HPs), which represent the first committed step in the synthesis of metabolites that function as signals and defences in plants. HPs are the initial substrates for different branches of the oxylipin pathway, and some plant species may express different LOX isoforms that supply specific branches. Here, we compare isogenic lines of the wild tobacco Nicotiana attenuata with reduced expression of NaLOX2 (irlox2) or NaLOX3 (irlox3) to determine the role of these different LOX isoforms in supplying substrates for two different pathways: green leaf volatiles (GLVs) and jasmonic acid (JA). Reduced NaLOX2 expression strongly decreased the production of GLVs without influencing the formation of JA and JA-related secondary metabolites. Conversely, reduced NaLOX3 expression strongly decreased JA biosynthesis, without influencing GLV production. The temporal expression of NaLOX2 and NaLOX3 also differed after elicitation; NaLOX3 was rapidly induced, attaining highest transcript levels within 1 h after elicitation, whereas NaLOX2 transcripts reached maximum levels after 14 h. These results demonstrate that N. attenuata channels the flux of HPs through the activities of different LOXs, leading to different direct and indirect defence responses mediating the plant's herbivore resistance.