Pectin methyl esterase inhibits intrusive and symplastic cell growth in developing wood cells of Populus.
Wood cells, unlike most other cells in plants, grow by a unique combination of intrusive and symplastic growth. Fibers grow in diameter by diffuse symplastic growth, but they elongate solely by intrusive apical growth penetrating the pectin-rich middle lamella that cements neighboring cells together. In contrast, vessel elements grow in diameter by a combination of intrusive and symplastic growth. We demonstrate that an abundant pectin methyl esterase (PME; EC 3.1.1.11) from wood-forming tissues of hybrid aspen (Populus tremula x tremuloides) acts as a negative regulator of both symplastic and intrusive growth of developing wood cells. When PttPME1 expression was up- and down-regulated in transgenic aspen trees, the PME activity in wood-forming tissues was correspondingly altered. PME removes methyl ester groups from homogalacturonan (HG) and transgenic trees had modified HG methylesterification patterns, as demonstrated by two-dimensional nuclear magnetic resonance and immunostaining using PAM1 and LM7 antibodies. In situ distributions of PAM1 and LM7 epitopes revealed changes in pectin methylesterification in transgenic trees that were specifically localized in expanding wood cells. The results show that en block deesterification of HG by PttPME1 inhibits both symplastic growth and intrusive growth. PttPME1 is therefore involved in mechanisms determining fiber width and length in the wood of aspen trees.
Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, SE 901 83 Umeå, Sweden.
Anna
A
Siedlecka
Susanne
S
Wiklund
Marie-Amélie
MA
Péronne
Fabienne
F
Micheli
Joanna
J
Lesniewska
Ingmar
I
Sethson
Ulf
U
Edlund
Luc
L
Richard
Björn
B
Sundberg
Ewa J
EJ
Mellerowicz
D002265:Carboxylic Ester Hydrolases / Q000378:metabolism*; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D007120:Immunochemistry; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D032107:Populus / Q000166:cytology* / Q000201:enzymology* / Q000254:growth & development; D020033:Protein Isoforms; D014934:Wood / Q000166:cytology* / Q000201:enzymology* / Q000254:growth & development
D010940:Plant Proteins; D020033:Protein Isoforms; D002265:Carboxylic Ester Hydrolases; C022323:pectinesterase