Down-regulation of UDP-glucuronic Acid Biosynthesis Leads to Swollen Plant Cell Walls and Severe Developmental Defects Associated with Changes in Pectic Polysaccharides

Rebecca Reboul,Ursula Lütz-Meindl,Raimund Tenhaken,Renaud Léonard,Beat Frey,Doris Wittmann,Martin Pabst,Claudia Geserick

doi:10.1074/jbc.m111.255695

Abstract

UDP-glucose dehydrogenase (UGD) plays a key role in the nucleotide sugar biosynthetic pathway, as its product UDP-glucuronic acid is the common precursor for arabinose, xylose, galacturonic acid, and apiose residues found in the cell wall. In this study we characterize an Arabidopsis thaliana double mutant ugd2,3 that lacks two of the four UGD isoforms. This mutant was obtained from a cross of ugd2 and ugd3 single mutants, which do not show phenotypical differences compared with the WT. In contrast, ugd2,3 has a strong dwarfed phenotype and often develops seedlings with severe root defects suggesting that the UGD2 and UGD3 isoforms act in concert. Differences in its cell wall composition in comparison to the WT were determined using biochemical methods indicating a significant reduction in arabinose, xylose, apiose, and galacturonic acid residues. Xyloglucan is less substituted with xylose, and pectins have a reduced amount of arabinan side chains. In particular, the amount of the apiose containing side chains A and B of rhamnogalacturonan II is strongly reduced, resulting in a swollen cell wall. The alternative pathway to UDP-glucuronic acid with the key enzyme myo-inositol oxygenase is not up-regulated in ugd2,3. The pathway also does not complement the ugd2,3 mutation, likely because the supply of myo-inositol is limited. Taken together, the presented data underline the importance of UDP GlcA for plant primary cell wall formation.

Highlights

Arabidopsis plants with a knock-out in UDP-glucose dehydrogenase provide less nucleotide sugars for cell wall biosynthesis
UDP-glucose dehydrogenase (UGD) plays a key role in the nucleotide sugar biosynthetic pathway, as its product UDP-glucuronic acid is the common precursor for arabinose, xylose, galacturonic acid, and apiose residues found in the cell wall
UGD2 and UGD3 showed the highest expression among the isoforms during plant development (Fig. 2A), as indicated by the microarray data visualized with Genevestigator [26] and in agreement with RT-PCR and ␤ glucuronidase-reporter gene analyses performed by Klinghammer and Tenhaken [9]

Summary

Background

Arabidopsis plants with a knock-out in UDP-glucose dehydrogenase provide less nucleotide sugars for cell wall biosynthesis. UDP-glucose dehydrogenase (UGD) plays a key role in the nucleotide sugar biosynthetic pathway, as its product UDP-glucuronic acid is the common precursor for arabinose, xylose, galacturonic acid, and apiose residues found in the cell wall. Arabidopsis thaliana possesses about 10 different types of epimerases, decarboxylases, and dehydrogenases involved in the biosynthesis of the nucleotide sugars They are all encoded by small gene families with typically two to six isoforms. UDP-GlcA acts as an important precursor in the synthesis of many different polysaccharides contributing to up to 50% of A. thaliana cell wall biomass. This may compete with sucrose synthesis and thereby limit the amount of soluble sugars

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION