Lipid Rafts in Higher Plant Cells

TLDR

Functional microdomains, or lipid rafts, are known in animal and yeast membranes to cluster sphingolipids and sterols, enabling protein sorting, signal transduction, and pathogen infection. The authors isolated plasma membrane proteins, separated them by one- and two-dimensional gel electrophoresis, and identified them using tandem mass spectrometry or specific antibodies. Plant plasma membranes contain lipid rafts enriched in glycosylceramide and sterols, exclude phospho- and glycoglycerolipids, and selectively recruit proteins such as NADPH oxidase upon elicitation while excluding others, including the small G protein NtRac5.

Abstract

A large body of evidence from the past decade supports the existence of functional microdomains in membranes of animal and yeast cells, which play important roles in protein sorting, signal transduction, or infection by pathogens. They are based on the dynamic clustering of sphingolipids and cholesterol or ergosterol and are characterized by their insolubility, at low temperature, in nonionic detergents. Here we show that similar microdomains also exist in plant plasma membrane isolated from both tobacco leaves and BY2 cells. Tobacco lipid rafts were found to be greatly enriched in a sphingolipid, identified as glycosylceramide, as well as in a mixture of stigmasterol, sitosterol, 24-methylcholesterol, and cholesterol. Phospho- and glycoglycerolipids of the plasma membrane were largely excluded from lipid rafts. Membrane proteins were separated by one- and two-dimensional gel electrophoresis and identified by tandem mass spectrometry or use of specific antibody. The data clearly indicate that tobacco microdomains are able to recruit a specific set of the plasma membrane proteins and exclude others. We demonstrate the recruitment of the NADPH oxidase after elicitation by cryptogein and the presence of the small G protein NtRac5, a negative regulator of NADPH oxidase, in lipid rafts.