Effect of pectin methylesterase gene expression on pea root development.

Expression of an inducible gene with sequences common to genes encoding pectin methylesterase (PME) was found to be tightly correlated, both spatially and temporally, with border cell separation in pea root caps. Partial inhibition of the gene's expression by antisense mRNA in transgenic pea hairy roots prevented the normal separation of root border cells from the root tip into the external environment. This phenotype was correlated with an increase in extracellular pH, reduced root elongation, and altered cellular morphology. The translation product of the gene exhibited PME activity in vitro. These results are consistent with the long-standing hypothesis that the demethylation of pectin by PME plays a key role in cell wall metabolism.