Towards Unravelling the Biological Significance of the Individual Components of Pectic Hairy Regions in Plants

Abstract

Highly branched pectins, which are comprised of a rhamnogalacturonan (RG I) backbone carrying galactan and arabinan side-chains, are generally referred to as hairy regions. Even though composition of the hairy regions has been well established in many plants, their biological function is still unknown. Developmental studies have already shown distinct antibody labelling patterns for the different epitopes present on the hairy region, suggesting that they may have different functions. This review compares the results from the developmental studies together with those from mutagenized and genetically modified plants with compositional alterations to the hairy region. In particular, the specific degradation of hairy regions, by the introduction of fungal enzymes in potato, enables the assignment of a putative biological function to the constituent polymers of the hairy region. We hypothesize that the most important function of the galactan hairs is to regulate the pore size of the cell wall. The deposition of galactan may restrict the access of modifying enzymes to the wall. In planta fragmentation of the RG I backbone shows severe histological modifications in potato tuber tissue. This suggests that the RG I backbone has an important function for normal potato tuber cell division and tissue development.