Improving Plant Nitrogen Use Efficiency through Alteration of Amino Acid Transport Processes

Abstract

Improving the efficiency of nitrogen (N) uptake and utilization in plants could potentially increase crop yields while reducing N fertilization and, subsequently, environmental pollution. Within most plants, N is transported primarily as amino acids. In this study, pea (Pisum sativum) plants overexpressing AMINO ACID PERMEASE1 (AAP1) were used to determine if and how genetic manipulation of amino acid transport from source to sink affects plant N use efficiency. The modified plants were grown under low, moderate, or high N fertilization regimes. The results showed that, independent of the N nutrition, the engineered plants allocate more N via the vasculature to the shoot and seeds and produce more biomass and higher seed yields than wild-type plants. Dependent on the amount of N supplied, the AAP1-overexpressing plants displayed improved N uptake or utilization efficiency, or a combination of the two. They also showed significantly increased N use efficiency in N-deficient as well as in N-rich soils and, impressively, required half the amount of N to produce as many fruits and seeds as control plants. Together, these data support that engineering N allocation from source to sink presents an effective strategy to produce crop plants with improved productivity as well as N use efficiency in a range of N environments.Nitrogen (N) is an essential nutrient that plants require in large amounts for growth and development. In industrial countries, high N fertilization enables maximum crop yields, and in the last 50 years, the use of synthetic N fertilizers has increased dramatically to meet the agricultural demands of a growing population (FAO, 2012;Conant et al., 2013). However, depending on the crop species and soil conditions, plants take up less than half of the applied N fertilizer (Raun and Johnson, 1999;Hodge et al., 2000;Kumar and Goh, 2002;Yang et al., 2015;Zhu et al., 2016). The remaining soil N may contaminate aquatic systems through runoffs or leached water (Crews and Peoples, 2005;Gruber and Galloway, 2008) or it may undergo denitrification and be released into the atmosphere as nitrous oxide, a powerful greenhouse gas (Bouwman, 1996;Bouwman et al., 2002), altogether resulting in negative effects on the environment and human health. Oppositely, in developing countries, access to N fertilizer is limited, and insufficient N nutrition results in low crop productivity and, ultimately, in reduced food supply (Brown et al., 2009;Lal, 2009).One solution to these issues is the production of crop varieties that are highly efficient in using N and produce high yields with reduced N input (MasclauxDaubresse et al., 2010;McAllister et al., 2012;Garnett et al., 2015). Plant nitrogen use efficiency (NUE) is determined by plant seed yield relative to the amount of N applied and is generally composed of both N uptake and N utilization efficiency (Moll et al., 1982). Nitrogen uptake efficiency (NUpE) is defined as total shoot N relative to the amount of N supplied to the soil. The uptake of N by the root is influenced by th...

Source and sink mechanisms of nitrogen transport and use

“…As a general concept, N source to sink partitioning is influenced by N uptake and metabolism in source organs, as well as the ability of sources to export, and sinks to import, the N. Studies in Arabidopsis and legumes have demonstrated that amino acid transport processes in the shoot exert regulatory control over N uptake in roots, source metabolism, and allocation to sinks. For example, in pea, increased amino acid phloem loading positively affected N root uptake and, subsequently, N availability for assimilation and usage in source and sink Zhang et al, 2015;Perchlik & Tegeder, 2017). Enhanced N export from leaves and associated changes in leaf N concentrations probably induced a shoot-to-root signal triggering up-regulation of N uptake and delivery to leaves.…”

“…Current knowledge regarding how amino acid transporters are controlled is mostly limited to transcriptional studies. Transporter expression was found to be cell-and tissue-specific, developmentally regulated, and affected by abiotic or biotic factors such as N, light, salt and drought stress, and nematode or pathogen attack (Pratelli & Pilot, 2014;Hav e et al, 2016;Perchlik & Tegeder, 2017). Changes in the redox status or other endogenous factors may induce the transcriptional changes (Geigenberger & Fernie, 2014;Noctor et al, 2015;Bellegarde et al, 2017;Gulyas et al, 2017).…”

“…The AAP1 pea plants were also used to determine if and how changes in source-to-sink amino acid transport affect plant NUE Perchlik & Tegeder, 2017). When grown under high, moderate or low N supplies, the transgenic lines always outperformed wild type.…”

Elevated CO2and warming change the nutrient status and use efficiency ofPanicum maximumJacq

“…The increased NUE of N under warmed plots with unchanged N content indicated that P. maximum acclimates to moderate heating. This response may be associated with changes in N uptake and assimilation, allocation and remobilisation or metabolic modifications [28]. Increased NUE of N may also be achieved by higher transpiration rates.…”

Late‐sown winter wheat requires less nitrogen input but maintains high grain yield

“…To meet the rising global demand for food, the NUE must be improved and the application of N fertilizer must be reduced (Hirel, Le Gouis, Ney, & Gallais, 2007; White & Brown, 2010). The main strategy to achieve this is to increase crop yields and reduce N fertilizer application by increasing the UPE and UTE in plants, to ultimately improve NUE and reduce environmental pollution (Perchlik & Tegeder, 2017). Ultimately, this involves achieving an ideal state whereby the maximum N absorption and photosynthetic production can be achieved by optimizing the light, water, and photosynthetic canopy under conditions of the lowest possible N fertilizer application (Fageria, Baligar, & Li, 2008), however, it is difficult to achieve.…”