Abstract
A large body of evidence from the past decade supports the existence, in membrane from animal and yeast cells, of functional microdomains that play important roles in protein sorting, signal transduction, or infection by pathogens. Recent reports demonstrated the presence, in plants, of detergent-resistant fractions isolated from plasma membrane. Analysis of the lipidic composition of this fraction revealed its enrichment in sphingolipids and sterols and depletion in phospho- and glycerolipids as previously observed for animal microdomains. One-dimensional gel electrophoresis experiments indicated that these detergent-resistant fractions are able to recruit a specific set of plasma membrane proteins and exclude others. In the present study, we used mass spectrometry to give an extensive description of a tobacco plasma membrane fraction resistant to solubilization with Triton X-100. This led to the identification of 145 proteins whose functional and physicochemical characteristics were analyzed in silico. Parameters such as isoelectric point, molecular weight, number and length of transmembrane segments, or global hydrophobicity were analyzed and compared with the data available concerning plant plasma membrane proteins. Post-translational modifications, such as myristoylation, palmitoylation, or presence of a glycosylphosphatidylinositol anchor, were examined in relation to the presence of the corresponding proteins in these microdomains. From a functional point of view, this analysis indicated that if a primary function of the plasma membrane, such as transport, seems under-represented in the detergent-resistant fraction, others undergo a significant increase of their relative importance. Among these are signaling and response to biotic and abiotic stress, cellular trafficking, and cell wall metabolism. This suggests that these domains are likely to constitute, as in animal cells, signaling platforms involved in these physiological functions.
Highlights
A large body of evidence from the past decade supports the existence, in membrane from animal and yeast cells, of functional microdomains that play important roles in protein sorting, signal transduction, or infection by pathogens
The absence of monogalactosyldiacylglycerol indicated a lack of contamination by thylakoid envelope. These results indicate that this plasma membrane (PM) fraction, contaminated very little by other endomembranes, constitutes a suitable starting material for extraction of detergent-resistant membranes (DRMs) and for further proteomic analysis
Previous studies performed on plant DRMs led to the identification of 11 proteins enriched in DRMs from tobacco Bright Yellow 2 (BY-2) cell plasma membrane, 35 proteins present in DRMs obtained from microsomes of A. thaliana callus, and 34 proteins present in DRMs of A. thaliana cotyledons plasma membrane [32]
Summary
A large body of evidence from the past decade supports the existence, in membrane from animal and yeast cells, of functional microdomains that play important roles in protein sorting, signal transduction, or infection by pathogens. We used mass spectrometry to give an extensive description of a tobacco plasma membrane fraction resistant to solubilization with Triton X-100 This led to the identification of 145 proteins whose functional and physicochemical characteristics were analyzed in silico. From a functional point of view, this analysis indicated that if a primary function of the plasma membrane, such as transport, seems under-represented in the detergent-resistant fraction, others undergo a significant increase of their relative importance Among these are signaling and response to biotic and abiotic stress, cellular trafficking, and cell wall metabolism. Preliminary studies have indicated the presence in these domains of typical plant plasma membrane proteins such as different isoforms of Hϩ-ATPase and the water channels, aquaporins They suggested a possible enrichment in signaling components such as leucin-rich repeat receptor kinases or small GTP-binding proteins. The limits of these few tentative studies (summarized in Ref. 11) are that each of them was incomplete and that they were performed on various plant materials (detergent-resistant membranes extracted from plasma membranes of tobacco leaves, mustard cotyledons, or Arabidopsis cotyledons or from microsomal membranes of Arabidopsis callus)
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