AtDUR3 represents the major transporter for high‐affinity urea transport across the plasma membrane of nitrogen‐deficient Arabidopsis roots

Abstract

SummaryDespite the fact that urea is a ubiquitous nitrogen source in soils and the most widespread form of nitrogen fertilizer used in agricultural plant production, membrane transporters that might contribute to the uptake of urea in plant roots have so far been characterized only in heterologous systems. Two T-DNA insertion lines, atdur3-1 and atdur3-3, that showed impaired growth on urea as a sole nitrogen source were used to investigate a role of the H + /urea co-transporter AtDUR3 in nitrogen nutrition in Arabidopsis. In transgenic lines expressing AtDUR3-promoter:GFP constructs, promoter activity was upregulated under nitrogen deficiency and localized to the rhizodermis, including root hairs, as well as to the cortex in more basal root zones. Protein gel blot analysis of two-phase partitioned root membrane fractions and whole-mount immunolocalization in root hairs revealed the plasma membrane to be enriched in AtDUR3 protein. Expression of the AtDUR3 gene in nitrogen-deficient roots was repressed by ammonium and nitrate but induced after supply of urea. Higher accumulation of urea in roots of wild-type plants relative to atdur3-1 and atdur3-3 confirmed that urea was the substrate transported by AtDUR3. Influx of 15 N-labeled urea in atdur3-1 and atdur3-3 showed a linear concentration dependency up to 200 lM external urea, whereas influx in wild-type roots followed saturation kinetics with an apparent K m of 4 lM. The results indicate that AtDUR3 is the major transporter for high-affinity urea uptake in Arabidopsis roots and suggest that the high substrate affinity of AtDUR3 reflects an adaptation to the low urea levels usually found in unfertilized soils.

Nitrogen acquisition by roots: physiological and developmental mechanisms ensuring plant adaptation to a fluctuating resource

“…Concerning urea, molecular analysis of AtDUR3 expression showed that its expression is downregulated by NO 3 − and NH 4 + , but markedly induced by supply of urea (Fig. 3, Kojima et al 2007). Yet no further progress had been done to delineate this complex regulation.…”

“…A. thaliana plants possess a high-affinity urea transporter (DUR3, Fig. 1) that is involved in taking up environmental urea but may also mediate internal urea transport (Liu et al 2003a;Kojima et al 2007). DUR3 was identified by its similarity to the urea transporter of Saccharomyces cerevisiae (ScDUR3), and was shown to account for most of the root urea HATS activity ).…”

Molecular and physiological interactions of urea and nitrate uptake in plants

“…8 On the other hand, the effect of nitrate to limit urea uptake was sustained by a down regulation of urea transporter DUR3 when inorganic N source, nitrate or ammonium nitrate, were supplied along with urea. 8,39,42 Further transcriptional changes of the assimilation pathways were identified when both sources were applied in the external solution. Microarray data in Arabidopsis and maize, revealed that urea and nitrate treatment in comparison to nitrate alone increased the up-regulation of nitrate-responsive genes, in particular of those involved in the uptake and assimilation of nitrate.…”

Improving Nitrogen Use Efficiency in Crops for Sustainable Agriculture

“…It is well known that urea is absorbed as an intact molecule by plant leaves and roots [116] by means of specific root transporters [117,118]. Although the use of urea is mainly as a source of N fertilizer, the contribution of plant urea uptake and metabolism in a physiological and agricultural context is still not investigated.…”