First published online June 10, 2005; 10.1104/pp.105.059865
Plant Physiology 138:1334-1346 (2005)
© 2005 American Society of Plant Biologists
CELL BIOLOGY AND SIGNAL TRANSDUCTION
Pectin Methylesterase, a Regulator of Pollen Tube Growth1,[w]
Maurice Bosch*,
Alice Y. Cheung and
Peter K. Hepler
Biology Department (M.B., P.K.H.), Department of Biochemistry and Molecular Biology (A.Y.C.), and Plant Biology Graduate Program (A.Y.C., P.K.H.), University of Massachusetts, Amherst, Massachusetts 01003
The apical wall of growing pollen tubes must be strong enough to withstand the internal turgor pressure, but plastic enough to allow the incorporation of new membrane and cell wall material to support polarized tip growth. These essential rheological properties appear to be controlled by pectins, which constitute the principal component of the apical cell wall. Pectins are secreted as methylesters and subsequently deesterified by the enzyme pectin methylesterase (PME) in a process that exposes acidic residues. These carboxyls can be cross-linked by calcium, which structurally rigidifies the cell wall. Here, we examine the role of PME in cell elongation and the regulation of its secretion and enzymatic activity. Application of an exogenous PME induces thickening of the apical cell wall and inhibits pollen tube growth. Screening a Nicotiana tabacum pollen cDNA library yielded a pollen-specific PME, NtPPME1, containing a pre-region and a pro-region. Expression studies with green fluorescent protein fusion proteins show that the pro-region participates in the correct targeting of the mature PME. Results from in vitro growth analysis and immunolocalization studies using antipectin antibodies (JIM5 and JIM7) provide support for the idea that the pro-region acts as an intracellular inhibitor of PME activity, thereby preventing premature deesterification of pectins. In addition to providing experimental data that help resolve the significance and function of the pro-region, our results give insight into the mechanism by which PME and its pro-region regulate the cell wall dynamics of growing pollen tubes.
1 This work was supported by the National Science Foundation (grant no. MCB0077599 to P.K.H. and grant no. BBS8714235 to the University of Massachusetts Central Microscope Facility), and by the U.S. Department of Agriculture (grant no. 0101936 to A.Y.C.).
[w] The online version of this article contains Web-only data.
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.059865.
* Corresponding author; e-mail mbosch{at}bio.umass.edu; fax 4135453243.
Received January 18, 2005;
returned for revision March 15, 2005;
accepted March 15, 2005.
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