Abstract
Nucleotide sugars are synthesized through both de novo and salvage pathway, and serve as glycosyl donors for the synthesis of polysaccharides in higher plants. UDP-sugar pyrophosphorylase catalyzes the conversion of various monosaccharide 1-phosphates to UDP-sugars. Using genomic database, a putative gene of Arabidopsis has been identified as UDP-sugar pyrophosphorylase. The gene, designated AtUSP, encodes a protein with 614 amino acids, and shares high similarity with a UDP-sugar pyrophosphorylase from pea. AtUSP was expressed in young seedlings, rosette leaves, and flowers of Arabidopsis, and relatively strong expression was detected in the vascular tissue of leaves and the pollens. Recombinant AtUSP expressed in Escherichia coli exhibited broad specificity toward monosaccharide 1-phosphates forming various UDP-sugars such as UDP-Glc, UDP-Gal, UDP-GlcA, UDP-Xyl, and UDP-L-Ara. A mutation in AtUSP< gene caused by T-DNA insertion completely abolished male fertility, indicating that AtUSP plays an essential role in the salvage pathway in pollen development or germination.
