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

Authors: VU, HIEU - Kansas State University; ROTH, MARY - Kansas State University; TAMURA, PAMELA - Kansas State University; SAMARAKOON, THILANI - Kansas State University; SHIVA, SUNITHA - Kansas State University; HONEY, SAMUEL - Kansas State University; LOWE, KALEB - Kansas State University; Schmelz, Eric; WILLIAMS, TODD - University Of Kansas; WELTI, RUTH - Kansas State University

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2013
Publication Date: 4/1/2014
Citation: Vu, H.S., Roth, M.R., Tamura, P., Samarakoon, T., Shiva, S., Honey, S., Lowe, K., Schmelz, E.A., Williams, T.D., Welti, R. 2014. Head-group acylation of monogalactosyldiacylglycerol is a common stress response, but the acyl-galactose acyl composition varies with the plant species and applied stress. Physiologia Plantarum. 150:517-528.

Interpretive Summary: Crop plant damage caused by biotic and abiotic stress including mechanical wounding, pathogens and freezing is known to dramatically alter the lipid composition of cell membranes. Despite the essential role of membrane lipids in plant growth and defense, the complexity and precise physiological roles of these changes remains poorly understood. In collaboration with researchers at Kansas State University, scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL, have discovered that wheat (Triticum aestivum), tomato (Solanum lycopersicum), and arabidopsis (Arabidopsis thaliana) all demonstrate rapid wound-induced acylation of monogalactosyldiacylglycerol however proportions of the acyl-galactose components differ. Wounding and pathogen infection promotes the acylation of oxidized fatty acids while freeze damage results in the esterification of non-oxidized fatty acids to galactose. Based on numerous experiments, stress induced pools of acylated monogalactosyldiacylglycerol appear to function as a mechanism to sequester potentially harmful fatty acids from the plant cell membrane. These results demonstrate the complexity of membrane lipid dynamics following plant stress and suggests that these conjugates may not be further sources of bioactive phytohormones following subsequent stress.

Technical Abstract: Head group acylation of monogalactosyldiacylglycerol is a plant lipid modification occurring during bacterial infection. Little is known about the range of stresses that induce this lipid modification, the molecular species induced, and the function of the modification. Lipidomic analysis using triple quadrupole mass spectrometry characterized molecular species of galactose-acylated monogalactosyldiacylglycerols (acMGDG) formed during stress responses in wheat (Triticum aestivum), tomato (Solanum lycopersicum), and Arabidopsis thaliana. Analysis of leaf lipids after mechanical wounding indicates that, in response to the same stress, different plant species accumulate acMGDG with different acyl-galactose components. 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. In Arabidopsis, concentration of oxidized fatty acids on the galactosyl ring of acMGDG indicates that the acMGDG pool sequesters oxidized fatty acids during stress responses. In conclusion, acMGDG formation is a common stress response but the composition of acMGDG varies among plant species and depends on the applied stress