Rice DUR3 mediates high‐affinity urea transport and plays an effective role in improvement of urea acquisition and utilization when expressed in Arabidopsis

Abstract

Summary Despite the great agricultural and ecological importance of efficient use of urea‐containing nitrogen fertilizers by crops, molecular and physiological identities of urea transport in higher plants have been investigated only in Arabidopsis. We performed short‐time urea‐influx assays which have identified a low‐affinity and high‐affinity (Km of 7.55 μM) transport system for urea‐uptake by rice roots (Oryza sativa). A high‐affinity urea transporter OsDUR3 from rice was functionally characterized here for the first time among crops. OsDUR3 encodes an integral membrane‐protein with 721 amino acid residues and 15 predicted transmembrane domains. Heterologous expression demonstrated that OsDUR3 restored yeast dur3‐mutant growth on urea and facilitated urea import with a Km of c. 10 μM in Xenopus oocytes. Quantitative reverse‐transcription polymerase chain reaction (qPCR) analysis revealed upregulation of OsDUR3 in rice roots under nitrogen‐deficiency and urea‐resupply after nitrogen‐starvation. Importantly, overexpression of OsDUR3 complemented the Arabidopsis atdur3‐1 mutant, improving growth on low urea and increasing root urea‐uptake markedly. Together with its plasma membrane localization detected by green fluorescent protein (GFP)‐tagging and with findings that disruption of OsDUR3 by T‐DNA reduces rice growth on urea and urea uptake, we suggest that OsDUR3 is an active urea transporter that plays a significant role in effective urea acquisition and utilisation in rice.

Isolation and functional characterization of a high affinity urea transporter from roots of Zea mays

“…The region containing the other two substitutions was not covered by ESTs. However, the presence of asparagine (N) and histidine (H) instead of lysine (K) and glutamine (Q), respectively, was also found in the amino-acid sequence of rice OsDUR3 [19]. …”

“…AtDUR3 showed no significant homology to any other protein of Arabidopsis [13]. Similarly, in the rice genome, OsDUR3 is the only gene that has significant homology to AtDUR3 , suggesting that plant DUR3 proteins might represent a transporter subfamily consisting of only one member [18,19]. To date, in higher plants only Arabidopsis and rice DUR3 have been characterized at the molecular and physiological level [13,18,19].…”

Molecular and physiological interactions of urea and nitrate uptake in plants

“…Experimental evidence suggests that DUR3 is the main component of the high affinity transport system for urea acquisition in roots and the expression of DUR3 gene appears to be induced under N starvation. 12,37,38 Data reported in Arabidopsis and maize have revealed that the urea acquisition is induced by the presence in the external solution of the substrate itself. 8,39 In particular in maize roots, the high affinity transport system of urea appeared to be inducible by urea itself, retro-regulated and dependent on the external urea concentration and on the duration of root exposure to the N source.…”

Reversal of senescence by N resupply to N-starved Arabidopsis thaliana: transcriptomic and metabolomic consequences

“…For example, Gu et al (2013) observed an up-regulation of the two Zea mays (corn) ammonium transporter genes ZmAMT1;1a and ZmAMT1;3 when ammonium, but not nitrate, was resupplied after N starvation, indicating a substrate-specific regulation. Wang et al (2012) analysed expression of the high-affinity urea transporter gene OsDUR3 from rice ( Oryza sativa ) and found that it is generally up-regulated in roots during N depletion; in addition it can be specifically induced by the addition of urea, but not by ammonium, also indicating a substrate-specific regulation. In addition to effects on gene expression, Engelsberger and Schulze (2012) recently reported that N resupply leads to alterations in protein phosphorylation patterns within minutes after addition of N in the form of either nitrate or ammonium.…”