The Arabidopsis tonoplast is almost devoid of N-glycosylated proteins, unlike the rat lysosomal membrane

About one third of secretory proteins are N-glycosylated. N-glycans can be modified when proteins travel through the Golgi complex. Using in silico and experimental approaches we analyzed the distribution of the N-glycoproteome in the vacuolar (tonoplast) or plasma membrane (PM) of Arabidopsis. We show that the tonoplast is virtually devoid of proteins with Golgi-modified glycans and contains only a small proportion, if any, of the N-glycoproteome, which is instead enriched in the PM. Lysosomes share with vacuoles the hydrolytic functions and the position along the secretory pathway. However, we show that the percentage of N-glycoproteome of the rat lysosomal and plasma membranes are much higher than that of the tonoplast, and are very similar to that of the Arabidopsis PM. We propose that protection against the luminal hydrolases, which seems to have been achieved in lysosomal membrane proteins by extensive N-glycosylation, has instead been mainly obtained in tonoplast proteins by limiting the length of their luminal domains. Our results cast light on the biogenesis and evolution of hydrolytic compartments in plants and animals and open new questions: i) Does the scarcity of glycoproteins indicate that the major route to the tonoplast bypasses the Golgi apparatus? ii) Are N-glycans involved in targeting to the plant plasma membrane?