Abstract
Low nitrogen availability is one of the main limiting factors for plant growth and development, and high doses of N fertilizers are necessary to achieve high yields in agriculture. However, most N is not used by plants and pollutes the environment. This situation can be improved by enhancing the nitrogen use efficiency (NUE) in plants. NUE is a complex trait driven by multiple interactions between genetic and environmental factors, and its improvement requires a fundamental understanding of the key steps in plant N metabolism—uptake, assimilation, and remobilization. This review summarizes two decades of research into bioengineering modification of N metabolism to increase the biomass accumulation and yield in crops. The expression of structural and regulatory genes was most often altered using overexpression strategies, although RNAi and genome editing techniques were also used. Particular attention was paid to woody plants, which have great economic importance, play a crucial role in the ecosystems and have fundamental differences from herbaceous species. The review also considers the issue of unintended effects of transgenic plants with modified N metabolism, e.g., early flowering—a research topic which is currently receiving little attention. The future prospects of improving NUE in crops, essential for the development of sustainable agriculture, using various approaches and in the context of global climate change, are discussed.
Highlights
Four families of transmembrane proteins are involved in NO3 − absorption from soil solution and transport: nitrate transporter 1 (NRT1)/peptide transporter (PTR) family (NPF), NRT2, chloride channel (CLC) family, and slowly activating anion channel [3]
OsAMT1.1 is the most active and/or most N-responsive gene of high-affinity NH4 + membrane transporter, but its overexpression under the pUbi in rice hydroponically grown for 21 days at low or high NH4 + levels did not change or significantly reduced the biomass compared to control [71]
The authors believe that synthesis of 2-oxoglutarate is a key junction point of the carbohydrate and amino acid metabolic pathways, and that its accumulation upsets the balance of the primary metabolism of C and N, which affects the yield of maize
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The double increase in the world grain production over four decades (1960–2000) was achieved due to a two-fold increase in grain yields owing to a seven-fold increase in the use of N fertilizers [2]. Of crops and, preserve or even increase their productivity while reducing the use of N fertilizers. This will reduce both food cost and environmental pollution. Particular attention was paid to woody plants as well as the unintended effects of modified N metabolism in transgenic plants
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