Overexpression of UDP-sugar pyrophosphorylase leads to higher sensitivity towards galactose, providing new insights into the mechanisms of galactose toxicity in plants

Martina Althammer; Christof Regl; Klaus Herburger; Constantin Blöchl; Elena Voglas; Christian G Huber; Raimund Tenhaken

doi:10.1111/tpj.15638

Overexpression of UDP-sugar pyrophosphorylase leads to higher sensitivity towards galactose, providing new insights into the mechanisms of galactose toxicity in plants

Plant J. 2022 Mar;109(6):1416-1426. doi: 10.1111/tpj.15638. Epub 2022 Jan 2.

Authors

Martina Althammer¹, Christof Regl², Klaus Herburger³, Constantin Blöchl², Elena Voglas¹, Christian G Huber², Raimund Tenhaken¹

Affiliations

¹ Department of Biosciences, Molecular Plant Physiology, University of Salzburg, Hellbrunnerstr. 34, Salzburg, 5020, Austria.
² Department of Biosciences, Bioanalytical Research Labs, University of Salzburg, Hellbrunnerstr. 34, Salzburg, 5020, Austria.
³ Department of Plant and Environmental Sciences, Section for Plant Glycobiology, University of Copenhagen, Frederiksberg, 1871, Denmark.

Abstract

Galactose toxicity (Gal-Tox) is a widespread phenomenon ranging from Escherichia coli to mammals and plants. In plants, the predominant pathway for the conversion of galactose into UDP-galactose (UDP-Gal) and UDP-glucose is catalyzed by the enzymes galactokinase, UDP-sugar pyrophosphorylase (USP) and UDP-galactose 4-epimerase. Galactose is a major component of cell wall polymers, glycolipids and glycoproteins; therefore, it becomes surprising that exogenous addition of galactose leads to drastic root phenotypes including cessation of primary root growth and induction of lateral root formation. Currently, little is known about galactose-mediated toxicity in plants. In this study, we investigated the role of galactose-containing metabolites like galactose-1-phosphate (Gal-1P) and UDP-Gal in Gal-Tox. Recently published data from mouse models suggest that a reduction of the Gal-1P level via an mRNA-based therapy helps to overcome Gal-Tox. To test this hypothesis in plants, we created Arabidopsis thaliana lines overexpressing USP from Pisum sativum. USP enzyme assays confirmed a threefold higher enzyme activity in the overexpression lines leading to a significant reduction of the Gal-1P level in roots. Interestingly, the overexpression lines are phenotypically more sensitive to the exogenous addition of galactose (0.5 mmol L^-1 Gal). Nucleotide sugar analysis via high-performance liquid chromatography-mass spectrometry revealed highly elevated UDP-Gal levels in roots of seedlings grown on 1.5 mmol L^-1 galactose versus 1.5 mmol L^-1 sucrose. Analysis of plant cell wall glycans by comprehensive microarray polymer profiling showed a high abundance of antibody binding recognizing arabinogalactanproteins and extensins under Gal-feeding conditions, indicating that glycoproteins are a major target for elevated UDP-Gal levels in plants.

Keywords: UDP-sugar pyrophosphorylase; cell wall polymer profiling; galactose toxicity; galactose-1-phosphate; nucleotide sugars.

MeSH terms

Arabidopsis / enzymology*
Galactose* / toxicity
Sugars*
UDPglucose 4-Epimerase* / genetics
UDPglucose 4-Epimerase* / metabolism
UTP-Glucose-1-Phosphate Uridylyltransferase* / genetics
UTP-Glucose-1-Phosphate Uridylyltransferase* / metabolism
Uridine Diphosphate

Substances

Sugars
Uridine Diphosphate
UTP-Glucose-1-Phosphate Uridylyltransferase
UDPglucose 4-Epimerase
Galactose