Functional specialization of one copy of glutamine phosphoribosyl pyrophosphate amidotransferase in ureide production from symbiotically fixed nitrogen in Phaseolus vulgaris

Purines are essential molecules formed in a highly regulated pathway in all organisms. In tropical legumes, the nitrogen fixed in the nodules is used to generate ureides through the oxidation of de novo synthesized purines. Glutamine phosphoribosyl pyrophosphate amidotransferase (PRAT) catalyses the first committed step of de novo purine synthesis. In Phaseolus vulgaris there are three genes coding for PRAT. The three full‐length sequences, which are intron‐less genes, were cloned, and their expression levels were determined under conditions that affect the synthesis of purines. One of the three genes, PvPRAT3, is highly expressed in nodules and protein amount and enzymatic activity in these tissues correlate with nitrogen fixation activity. Inhibition of PvPRAT3 gene expression by RNAi‐silencing and subsequent metabolomic analysis of the transformed roots shows that PvPRAT3 is essential for the synthesis of ureides in P. vulgaris nodules. Purine de novo synthesis is a key process in all organisms, but even more in ureidic legumes, where it serves for the incorporation of the nitrogen fixed in the nodules. Glutamine phosphoribosylpyrophosphate amidotransferase, PRAT, catalyses the first and most regulated step of purine synthesis. The molecular analysis of the three PRATs from Phaseolus vulgaris reveals that only one isoform seems to be essential for the incorporation of the symbiotically fixed nitrogen and probably for the determination of ureidic metabolism in legumes, whereas the other two work to maintain the basal level of purine nucleotides in the leaves.