Pectin: cell biology and prospects for functional analysis

Pectin is a major component of primary cell walls of all land plants and en compasses a range of galacturonic acid-rich polysaccharides. Three major pe ctic polysaccharides (homogalacturonan, rhamnogalacturonan-I and rhamnogala cturonan-II) are thought to occur in all primary cell walls. This review su rveys what is known about the structure and function of these pectin domain s. The high degree of structural complexity and heterogeneity of the pectic matrix is produced both during biosynthesis in the endomembrane system and as a result of the action of an array of wall-based pectin-modifying enzym es. Recent developments in analytical techniques and in the generation of a nti-pectin probes have begun to place the structural complexity of pectin i n cell biological and developmental contexts. The in muro de-methyl-esterif ication of homogalacturonan by pectin methyl esterases is emerging as a key process for the local modulation of matrix properties. Rhamnogalacturonan- I comprises a highly diverse population of spatially and developmentally re gulated polymers, whereas rhamnogalacturonan-II appears to be a highly cons erved and stable pectic domain. Current knowledge of biosynthetic enzymes, plant and microbial pectinases and the interactions of pectin with other ce ll wall components and the impact of molecular genetic approaches are revie wed in terms of the functional analysis of pectic polysaccharides in plant growth and development.