Head‐group acylation of monogalactosyldiacylglycerol is a common stress response, and the acyl‐galactose acyl composition varies with the plant species and applied stress

Abstract

Formation of galactose-acylated monogalactosyldiacylglycerols has been shown to be induced by leaf homogenization, mechanical wounding, avirulent bacterial infection, and thawing after snap-freezing. Here, lipidomic analysis using mass spectrometry showed that galactose-acylated monogalactosyldiacylglycerols, formed in wheat (Triticum aestivum) and tomato (Solanum lycopersicum) leaves upon wounding, have acyl-galactose profiles that differ from those of wounded Arabidopsis thaliana, indicating that different plant species accumulate different acyl-galactose components in response to the same stress. Additionally, the composition of the acyl-galactose component of Arabidopsis acMGDG depends on the stress treatment. After sub-lethal freezing treatment, acMGDG contained mainly non-oxidized fatty acids esterified to galactose, whereas mostly oxidized fatty acids accumulated on galactose after wounding or bacterial infection. Compositional data are consistent with acMGDG being formed in vivo by transacylation with fatty acids from digalactosyldiacylglycerols. Oxophytodienoic acid, an oxidized fatty acid, was more concentrated on the galactosyl ring of acylated monogalactosyldiacylglycerols than in galactolipids in general. Also, oxidized fatty acid-containing acylated monogalactosyldiacylglycerols increased cumulatively when wounded Arabidopsis leaves were wounded again. These findings suggest that, in Arabidopsis, the pool of galactose-acylated monogalactosyldiacylglycerols may serve to sequester oxidized fatty acids during stress responses.

Modifications of membrane lipids in response to wounding of Arabidopsis thaliana leaves

“…6 MGDG acylation occurs when a fatty acyl chain is transferred from digalactosyldiacylglycerol (DGDG) to the 6-position on the galactose of MGDG, 7,8 producing an acylated MGDG and digalactosylmonoacylglycerol (DGMG) (Fig. 2, block a).…”

“…1C and D). 5,8,[11][12][13] Additionally phosphatidylglycerol (PG) with an acyl chain on the terminal glycerol and small amounts of head-group acylated DGDGs are also produced in Arabidopsis leaves when they are wounded (Fig. 1C).…”

“…1D), 5,8,12 plastidic lipids including PG, MGDG, DGDG, and acylated MGDG are converted to a plethora of oxidized molecular species during wounding (Fig. 2, block e).…”

Lipid changes after leaf wounding in Arabidopsis thaliana: expanded lipidomic data form the basis for lipid co‐occurrence analysis

“…Additionally, application of stress to a plant activates multiple metabolic pathways. In lipid metabolism, wounding stress causes phospholipase D activation, phospholipase A activation, oxidation of fatty acids on galactolipids, and head‐group acylation of monogalactosyldiacylglycerols (Narváez‐Vásquez et al ., ; Ryu, ; Buseman et al ., ; Zien et al ., ; Vu et al ., ). Steuer et al .…”

The activity of HYDROPEROXIDE LYASE 1 regulates accumulation of galactolipids containing 12-oxo-phytodienoic acid in Arabidopsis

“…Acyl-MGDG on the other hand appears to be ubiquitous in the plant kingdom (Heinz, 1967; Vu et al , 2014; Nilsson et al , 2015). It remains enigmatic as to why plants produce these lipids to such an extent following pathogen elicitation and mechanical wounding.…”