2012 Volume 24 Issue 135 Pages 13-23
L-Arabinofuranosyl (Araf) residues are a quantifiably important constituent of plant cell walls. The results of earlier studies have led to the hypothesis that UDP-L-arabinopyranose (UDP-Arap) is the sugar donor and that the conversion to Araf occurs during the glycosyl transfer reaction. However, this mechanism is unlikely because UDP-L-arabinofuranose (UDP-Araf) has been shown to be the sugar donor in the conversion of Araf-containing oligosaccharides in plant extracts. We speculated that UDP-Arap reacts with a mutase to form UDP-Araf and identified and partially characterized a rice UDP-L-arabinopyranose mutase (UAM) that catalyzes the interconversion of UDP-Arap and UDP-Araf. To investigate the effects of depleting Araf residues on cell wall structure and on rice growth and development, we used RNAi to suppress UAM expression in rice plants. Several transgenic plants had reduced proportions of Araf in their cell walls together with a decrease in the extent of substitution of the xylan backbone and a reduction of between 25% and 80% in ferulic acid and p-coumaric acid content. Transgenic plants with over 25% reduction in Araf residues were dwarfed and infertile. These results suggested that Araf residues are required for normal plant growth, development, and reproduction.
