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Plant Cell. 2016 Dec;28(12):2991-3004. doi: 10.1105/tpc.16.00186. Epub 2016 Nov 28.

Loss of Inositol Phosphorylceramide Sphingolipid Mannosylation Induces Plant Immune Responses and Reduces Cellulose Content in Arabidopsis.

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Joint BioEnergy Institute, Emeryville, California 94608.
Biological Systems and Engineering, Lawrence Berkeley National Laboratory, Berkeley, California 94720.
Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan.
Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720.
Cellulose Production Research Team, Biomass Engineering Program, Center for Sustainable Resource Science, RIKEN, Yokohama 230-0045, Japan.
Graduate School of Biological Sciences, Nara Institute of Science and Technology, 630-0192 Nara, Japan.
Plant and Microbial Biology, University of California, Berkeley, California 94720.
Joint BioEnergy Institute, Emeryville, California 94608


Glycosylinositol phosphorylceramides (GIPCs) are a class of glycosylated sphingolipids found in plants, fungi, and protozoa. These lipids are abundant in the plant plasma membrane, forming ∼25% of total plasma membrane lipids. Little is known about the function of the glycosylated headgroup, but two recent studies have indicated that they play a key role in plant signaling and defense. Here, we show that a member of glycosyltransferase family 64, previously named ECTOPICALLY PARTING CELLS1, is likely a Golgi-localized GIPC-specific mannosyl-transferase, which we renamed GIPC MANNOSYL-TRANSFERASE1 (GMT1). Sphingolipid analysis revealed that the Arabidopsis thaliana gmt1 mutant almost completely lacks mannose-carrying GIPCs. Heterologous expression of GMT1 in Saccharomyces cerevisiae and tobacco (Nicotiana tabacum) cv Bright Yellow 2 resulted in the production of non-native mannosylated GIPCs. gmt1 displays a severe dwarfed phenotype and a constitutive hypersensitive response characterized by elevated salicylic acid and hydrogen peroxide levels, similar to that we previously reported for the Golgi-localized, GIPC-specific, GDP-Man transporter GONST1 (Mortimer et al., 2013). Unexpectedly, we show that gmt1 cell walls have a reduction in cellulose content, although other matrix polysaccharides are unchanged.

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