UDP-sugar pyrophosphorylase controls the activity of proceeding sugar-1-kinases enzymes

Plant cell wall synthesis requires a number of different nucleotide sugars which provide the building blocks of the different polymers. These nucleotide sugars are mainly provided by de novo synthesis but recycling pathways also contribute to the pools. The last enzyme of the recycling pathway is UDP-sugar pyrophosphorylase (USP), a single copy gene in Arabidopsis, of which a knockout is lethal for pollen development. Here we analyze the dependency between USP enzyme activity and the upstream glucuronokinase. Gene silencing of USP by miRNA cause a concomitant reduction of USP and of glucuronokinase activity presumably to prevent the accumulation of sugar-1-phosphates interfering with normal metabolism and depleting the phosphate pool of the cell.