Abstract
Homogalacturonan (HG), which constitutes one of the major domains of pectin in plant cell walls, is highly methyl-esterified before secretion into the cell wall space, where it is demethyl-esterified by pectin methylesterases (PMEs). The de-esterification facilitates the cross-linking of HG domains via calcium bridges, thereby causing formation of pectin gel that gives mechanical strength to the cell wall matrix. Although PMEs are implicated in regulating mechanical properties of cell wall, functions of individual members of PME family are not clear. Our comprehensive analysis on cell wall related genes in Arabidopsis has identified AtPME61 as being expressed specifically in certain cell files within cortical cells of middle to basal part of stems. A null mutant for AtPME61, pme61, carries thinner and more fragile stems compared to wild type plants. We have also revealed that the pme61 exhibits lower degree of demethylesterification within cortex cells in basal part of stems and its PME activity is lower. Thus, we conclude that the AtPME61 works as a primary PME in the basal stem, and plays an essential role in formation of supporting tissue of Arabidopsis.
