Abnormal Glycosphingolipid Mannosylation Triggers Salicylic Acid–Mediated Responses in Arabidopsis[W][OA]

J. Mortimer,Xiaolan Yu,S. Albrecht,F. Sicilia,Mariela Huichalaf,D. Ampuero,L. Michaelson,A. Murphy,T. Matsunaga,Samantha Kurz,Elaine Stephens,T. C. Baldwin,T. Ishii,J. Napier,A. Weber,M. Handford,P. Dupree

Published 2013 in The Plant Cell

ABSTRACT

We showed that a Golgi sugar nucleotide transporter (GONST1) is not required for polysaccharide biosynthesis as previously hypothesized. Instead, we found that GONST1 provides substrate for the glycosylation of an abundant class of sphingolipid. gonst1 plants are stunted and display a constitutive defense response, including elevated salicylic acid and hydrogen peroxide levels. The Arabidopsis thaliana protein GOLGI-LOCALIZED NUCLEOTIDE SUGAR TRANSPORTER (GONST1) has been previously identified as a GDP-d-mannose transporter. It has been hypothesized that GONST1 provides precursors for the synthesis of cell wall polysaccharides, such as glucomannan. Here, we show that in vitro GONST1 can transport all four plant GDP-sugars. However, gonst1 mutants have no reduction in glucomannan quantity and show no detectable alterations in other cell wall polysaccharides. By contrast, we show that a class of glycosylated sphingolipids (glycosylinositol phosphoceramides [GIPCs]) contains Man and that this mannosylation is affected in gonst1. GONST1 therefore is a Golgi GDP-sugar transporter that specifically supplies GDP-Man to the Golgi lumen for GIPC synthesis. gonst1 plants have a dwarfed phenotype and a constitutive hypersensitive response with elevated salicylic acid levels. This suggests an unexpected role for GIPC sugar decorations in sphingolipid function and plant defense signaling. Additionally, we discuss these data in the context of substrate channeling within the Golgi.

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