Analysis of LuPME3, a pectin methylesterase from Linum usitatissimum, revealed a variability in PME proteolytic maturation
Résumé
Pectin methylesterase (PME) catalyzes the de-methylesterification of pectin in plant cell walls during cell elongation.1Pectins are mainly composed of a(1, 4)-D-galacturonosyl acid units that are synthesized in a methylesterified form in theGolgi apparatus to prevent any interaction with Ca2+ ions during their intracellular transport.2 The highly methylesterifiedpectins are then secreted into the apoplasm3 and subsequently de-methylesterified in muro by PMEs. This can eitherinduce the formation of pectin gels through the Ca2+ crosslinking of neighboring non-methylesterified chains or createsubstrates for pectin-degrading enzymes such as polygalacturonases and pectate lyases for the initiation of cell wallloosening.4 PMEs belong to a large multigene family. Sixt-six PME-related genes are predicted in the Arabidopsisgenome.1 Among them, we have recently shown that AtPME3 (At3g14310), a major basic PME isoform in A. thaliana, isubiquitously expressed in vascular tissues and play a role in adventitious rooting.5 In flax (Linum usitatissimum), threegenes encoding PMEs have been sequenced so far, including LuPME3, the ortholog of AtPME3. Analysis of the LuPME3isoform brings new insights into the processing of these proteins.