Specific Adduction of Plant Lipid Transfer Protein by an Allene Oxide Generated by 9-Lipoxygenase and Allene Oxide Synthase

Abstract

Lipid transfer proteins (LTPs) are ubiquitous plant lipidbinding proteins that have been associated with multiple developmental and stress responses. Although LTPs typically bind fatty acids and fatty acid derivatives in a non-covalent way, studies on the LTPs of barley seeds have identified an abundantly occurring covalently modified form, LTP1b, the lipid ligand of which has resisted clarification. In the present study, this adduct was identified as the ␣-ketol 9-hydroxy-10-oxo-12(Z)-octadecenoic acid. Further studies on the formation of LTP1b demonstrated that the ligand was introduced by nucleophilic attack of the free carboxylate group of the Asp-7 residue of the protein at carbon-9 of the allene oxide fatty acid 9(S),10-epoxy-10,12(Z)-octadecadienoic acid. This reactive oxylipin was produced in barley seeds by oxygenation of linoleic acid by 9-lipoxygenase followed by dehydration of the resulting hydroperoxide by allene oxide synthase. The generation of protein-oxylipin adducts represents a new function for plant allene oxide synthases, enzymes that have earlier been implicated mainly in the biosynthesis of the jasmonate family of plant hormones. Additionally, the LTP-allene oxide synthase interaction opens new perspectives regarding the roles of LTPs in the signaling of plant defense and development.

EBE, an AP2/ERF Transcription Factor Highly Expressed in Proliferating Cells, Affects Shoot Architecture in Arabidopsis

“…Several of the down-regulated genes encode lipid transfer proteins (AtLTP3, At5g59320; AtLTP4, At5g59310; AtLTP6, At3g08770; AtLTP12, At3g51590). LTPs are ubiquitous plant lipid-binding proteins proposed to function in various developmental and stress responses, signaling, and cell wall loosening (Kader, 1996;Bakan et al, 2006;Yeats and Rose, 2008). Furthermore, expression of the cell wall-loosening gene AtEXPB3 (At4g28250; encoding expansin) and the xyloglucan endotransglucosylase/ hydrolase genes AtXTH9 (At4g03210) and AtXTH19 (At4g30290) was markedly reduced upon EBE induction.…”

The biochemistry and biology of extracellular plant lipid‐transfer proteins (LTPs)

“…Bakan et al (2006) demonstrated that the LTP1b consisted of an allene oxide that is specifically adducted to barley LTP1 at Asp7 by the action of 9-lipoxygenase and allene oxide synthase. The similarity of the adduct structure to precursors of jasmonic acid suggests a role in signaling, although a role in trapping of toxic oxylipins may also be possible.…”

Utilization of the Linear Mode of MALDI-TOF Mass Spectrometry in the Study of Glycation During the Malting Process

“…Another form of LTP, named LTP1b, corresponds to LTP1 with a covalently linked lipid-like molecule of mass 294 Da, esterically bound to an aspartate residue. The lipid adduct was identified as 9,10-dihydroxy-12(Z)-octadecenoic acid 1 . The major MS signals representing the molecular masses in the range m/z 9,986 ± 4 Da correspond to LTP1b.…”