Urea transporter DUR3 gene in grasses: In silico characterization and relative expression in Megathyrsus maximus under different nitrogen sources

Nitrogen (N) is an indispensable macronutrient for crop growth and yield. The N can be acquired and assimilated from a variety of sources such as nitrate (NO₃⁻), ammonium (NH₄⁺), and urea [CO(NH₂)₂]. Due to its low cost, urea is a popular N source in pastures. The urea transporter DUR3 gene, which can mediate direct urea uptake by roots, has received little attention in grasses. The purpose of the current study was to identify and characterize in silico the DUR3 gene in 29 grass species in comparison to Arabidopsis thaliana. Physicochemical properties, gene structure, motifs, and phylogenetic tree relationships were predicted. Furthermore, the relative expression patterns of the DUR3 gene were evaluated in two commercial cultivars (Mombaça and Aruana) of Megathyrsus maximus. Plants were grown in a nutritive solution containing 2 mM of N supplied as NO₃⁻, NH₄⁺, or [CO(NH₂)₂]. To investigate the relative expression of the DUR3 gene in leaves and roots we used the 2^-ΔΔCt method. The in silico characterization revealed that the DUR3 gene is highly conserved among grasses. Plants were submitted to 3 days of N starvation and the tissue was harvested 3 h after transfer to ammonium or urea solution. In general, the DUR3 gene was down-regulated in leaves and up-regulated in roots for both cultivars. Twenty-four hours after transfer, only the Mombaça cultivar showed a significant decrease of DUR3 mRNA levels in leaves and an increase in roots under urea, demonstrating that the DUR3 gene expression pattern is variable between cultivars of M. maximus. Characterizing of the DUR3 gene in grasses is the first step toward biotechnological approaches aiming to improve urea uptake in pastures.