Abstract
Arabidopsis produces galactolipids containing esters of 12-oxo-phytodienoic acid (OPDA) and dinor-12-oxo-phytodienoic acid (dnOPDA). These lipids are referred to as arabidopsides and accumulate in response to abiotic and biotic stress. We explored the natural genetic variation found in 14 different Arabidopsis accessions to identify genes involved in the formation of arabidopsides. The accession C24 was identified as a poor accumulator of arabidopsides whereas the commonly used accession Col-0 was found to accumulate comparably large amounts of arabidopsides in response to tissue damage. A quantitative trait loci analysis of an F2 population created from a cross between C24 and Col-0 located a region on chromosome four strongly linked to the capacity to form arabidopsides. Expression analysis of HYDROPEROXIDE LYASE 1 (HPL1) showed large differences in transcript abundance between accessions. Transformation of Col-0 plants with the C24 HPL1 allele under transcriptional regulation of the 35S promoter revealed a strong negative correlation between HPL1 expression and arabidopside accumulation after tissue damage, thereby strengthening the view that HPL1 competes with ALLENE OXIDE SYNTHASE (AOS) for lipid-bound hydroperoxide fatty acids. We further show that the last step in the synthesis of galactolipid-bound OPDA and dnOPDA from unstable allene oxides is exclusively enzyme-catalyzed and not the result of spontaneous cyclization. Thus, the results presented here together with previous studies suggest that all steps in arabidopside biosynthesis are enzyme-dependent and apparently all reactions can take place with substrates being esterified to galactolipids.
Highlights
Enzymatic or non-enzymatic peroxidation of polyunsaturated fatty acids give rise to a group of products collectively known as oxylipins (Mosblech et al, 2009)
Transformation of Col-0 plants with the C24 HYDROPEROXIDE LYASE 1 (HPL1) allele under transcriptional regulation of the 35S promoter revealed a strong negative correlation between HPL1 expression and arabidopside accumulation after tissue damage, thereby strengthening the view that HPL1 competes with ALLENE OXIDE SYNTHASE (AOS) for lipid-bound hydroperoxide fatty acids
We further show that the last step in the synthesis of galactolipid-bound oxo-phytodienoic acid (OPDA) and dnOPDA from unstable allene oxides is exclusively enzyme-catalyzed and not the result of spontaneous cyclization
Summary
Enzymatic or non-enzymatic peroxidation of polyunsaturated fatty acids give rise to a group of products collectively known as oxylipins (Mosblech et al, 2009). In Arabidopsis and certain other plant species, mainly from the Brassicaceae family, (dn)OPDA can be found as esters on the glycerol backbone and/or acylated to the 6′-hydroxyl group of the sugar moiety of galactolipids (Stelmach et al, 2001; Hisamatsu et al, 2003, 2005; Andersson et al, 2006; Buseman et al, 2006; Nakajyo et al, 2006; Böttcher and Weiler, 2007; Kourtchenko et al, 2007; Nilsson et al, 2015) These lipids are sometimes referred to as arabidopsides. We found that the ability to accumulate these lipids in response to tissue disruption is highly variable between accessions and we propose that HPL1 plays a major role in regulating the levels of arabidopsides
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