The response of the maize nitrate transport system to nitrogen demand and supply across the lifecycle

Abstract

SummaryAn understanding of nitrate (NO À 3 ) uptake throughout the lifecycle of plants, and how this process responds to nitrogen (N) availability, is an important step towards the development of plants with improved nitrogen use efficiency (NUE). NO À 3 uptake capacity and transcript levels of putative high-and low-affinity NO À 3 transporters (NRTs) were profiled across the lifecycle of dwarf maize (Zea mays) plants grown at reduced and adequate NO À 3 . Plants showed major changes in high-affinity NO À 3 uptake capacity across the lifecycle, which varied with changing relative growth rates of roots and shoots. Transcript abundances of putative high-affinity NRTs (predominantly ZmNRT2.1 and ZmNRT2.2) were correlated with two distinct peaks in high-affinity root NO À 3 uptake capacity and also N availability. The reduction in NO À 3 supply during the lifecycle led to a dramatic increase in NO À 3 uptake capacity, which preceded changes in transcript levels of NRTs, suggesting a model with short-term post-translational regulation and longer term transcriptional regulation of NO À 3 uptake capacity.These observations offer new insight into the control of NO À 3 uptake by both plant developmental processes and N availability, and identify key control points that may be targeted by future plant improvement programmes to enhance N uptake relative to availability and/or demand.

ZD958 is a low-nitrogen-efficient maize hybrid at the seedling stage among five maize and two teosinte lines

“…Under N deficiency, many N transporters and proteins mediating N metabolism have differential expression or accumulation (Yang et al 2011;Liao et al 2012a;Schlüter et al 2012;Garnett et al 2013), although no specific genes mediating N uptake and assimilation were identified with differential expression in rice seedlings at the early stage of N limitation (Lian et al 2006). Here, we found eight genes regulating N assimilation with significant down-regulation at the transcriptional level in the ZD958 root after 12-day N deficiency (Fig.…”

“…Plants can directly absorb various N compounds such as nitrate, ammonium, urea, amino acids, peptides, and proteins; however, nitrate is the predominant N absorbed by crops (Yuan et al 2007;Paungfoo-Lonhienne et al 2008;Näsholm et al 2009;Tegeder and Rentsch 2010;Wang et al 2012). Nitrate uptake from the soil is mediated by a series of transporters such as NRT1.1, NRT2.1 and NRT2.2 in the root (Wang et al 2012;Garnett et al 2013). After entry into the root system, nitrate is either directly transported to the shoot or reduced as ammonium by nitrate reductase and nitrite reductase, followed by synthesis of amino acids or other organic nitrogenous molecules with the glutamine synthetase and glutamate synthetase as initial catalysts (Lam et al 1996;Xu et al 2012).…”

“…At the molecular level, N deficiency causes genome-wild changes in gene expression and carbon and N metabolism in arabidopsis (Bi et al 2007); however, genes regulating N uptake and assimilation showed no significant difference in N-deficient rice seedlings in contrast to quick changes in expression of genes mediating metabolism, protein synthesis, and transport facilitation (Lian et al 2006). In maize, N deficiency causes a series of changes in gene expression and protein accumulation directly affecting N uptake and metabolism, amino acid transport, and protein metabolism (Yang et al 2011;Liao et al 2012a;Schlüter et al 2012Schlüter et al , 2013Garnett et al 2013;Humbert et al 2013). However, little is known about how hybrid maize, especially dominant hybrids in the field, respond to N limitation at physiological and molecular levels, and whether they have similar or contrasting responses compared with inbred lines and wild maize?…”

Complex phylogeny and gene expression patterns of members of the NITRATE TRANSPORTER 1/PEPTIDE TRANSPORTER family (NPF) in wheat

“…Whilst Soly NPF6.10 root expression was nitrate inducible, the Soly NPF6.9 expression behaved constitutively (Lauter et al , 1996). Root expression analysis of two maize co-orthologous genes grown under low and adequate nitrate nutrition showed no response of either gene in relation to N-nutrition throughout the whole lifecycle (Garnett et al , 2013). This emphasizes the complexity and variation in gene regulation in relation to nutrient uptake in crop plants with complex genomes, in comparison to a simple genome model plant such as Arabidopsis .…”

High nitrate supply reduces growth in maize, from cell to whole plant

“…Plants were grown under a 14 h photoperiod at 25/20 • C temperature and 70/80% relative humidity (day/night). The light intensity at the canopy was 500 mol m −2 s −1 photons as described by Garnett et al (2013).…”