The role of glycolipids at the interface of plant-microbe interactions during nodulation and myorrhiza formation in Lotus japonicus

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Glycolipids are constituents of membranes at the boundary between plants and microorganisms. We are studying the role of galactoglycerolipids, sterol glucosides and glucosylceramides in the symbiotic interaction of Lotus japonicus plants with Mesorhizobium during nodulation or with the fungus Glomus during mycorrhiza formation. Because each glycolipid class consists of numerous molecular species, a quadrupole-time of flight mass spectrometry (Q-TOF MS) based method was developed for the measurement of glycoglycerolipids, sterol lipids and sphingolipids. This includes the first development of a method for the measurement of all sterol lipid classes in plants (free sterols, sterol glucosides, sterol esters, acylated sterol glucosides). Transgenic Lotus plants carrying RNAi constructs for the genes involved in the synthesis of glycolipids (DGD1, DGD2, SGT1, SGT2, GCS) were generated during the previous funding period. Lipid measurements by Q-TOF MS revealed that sterol glucosides and glucosylceramides are reduced in SGT2 and GCS RNAi lines, respectively. We obtained TILLING mutants for the Lotus genes DGD1, DGD2, SGT2 and GCS. Nodulation and mycorrhization experiments of the transgenic RNAi lines and of the mutant lines are underway. Furthermore, we developed a non-targeted Q-TOF MS approach that we will employ to search for lipids responding to nodulation or mycorrhization in Lotus.