Résumé
A thorough analysis, using mass spectrometry, of aquaporins expressed in plant root plasma membrane was performed, with the objective of revealing novel post-translational regulations. Here we show that the N-terminal tail of Plasma membrane Intrinsic Protein (PIP) aquaporins can exhibit multiple modifications and is differentially maturated between members of the PIP1 and PIP2 subclasses. Thus, the initiating methionine was acetylated or cleaved in native PIP1 and PIP2 isoforms, respectively. In addition, several residues were detected to be methylated in PIP2 aquaporins. Lys3 and Glu6 of PIP2;1, one of the most abundant aquaporins in the plasma membrane occurred as di- and mono-methylated residues, respectively. Ectopic expression in Arabidopsis suspension cells of PIP2;1, either wild-type or with altered methylation sites revealed an interplay between methylation at the two sites. Measurements of water transport in plasma membrane vesicles purified from these cells suggested that PIP2;1 methylation does not interfere with the aquaporin intrinsic water permeability. In conclusion, this study identifies methylation as a novel post-translational modification of aquaporins, and even plant membrane proteins and may represent a critical advance towards the identification of new regulatory mechanisms of membrane transport.