Abstract
Plant growth is the result of the coordinated photosynthesis-mediated assimilation of oxidized forms of C, N and S. Nitrate is the predominant N source in soils and its reductive assimilation requires the successive activities of soluble cytosolic NADH-nitrate reductases (NR) and plastid stroma ferredoxin-nitrite reductases (NiR) allowing the conversion of nitrate to nitrite and then to ammonium. However, nitrite, instead of being reduced to ammonium in plastids, can be reduced to nitric oxide (NO) in mitochondria, through a process that is relevant under hypoxic conditions, or in the cytoplasm, through a side-reaction catalyzed by NRs. We use a loss-of-function approach, based on CRISPR/Cas9-mediated genetic edition, and gain-of-function, using transgenic overexpressing HA-tagged Arabidopsis NiR1 to characterize the role of this enzyme in controlling plant growth, and to propose that the NO-related post-translational modifications, by S-nitrosylation of key C residues, might inactivate NiR1 under stress conditions. NiR1 seems to be a key target in regulating nitrogen assimilation and NO homeostasis, being relevant to the control of both plant growth and performance under stress conditions. Because most higher plants including crops have a single NiR, the modulation of its function might represent a relevant target for agrobiotechnological purposes.
Highlights
Plant growth is the result of the coordinated photosynthesis-mediated assimilation of oxidized forms of C, N and S
We found ubiquitylated nitrite reductase 1 (NiR1), it is unlikely that ubiquitylation-mediated proteolysis of NiR1 represents a relevant factor in controlling protein stability, as we did not find significant effects in either protein stability or nitrite reductase activity in plants treated with a proteasome inhibitor (Figure 5)
(2) Blocking nitrite reduction to ammonium in Arabidopsis plants containing a single nitrite reductase led to a strong increase in nitric oxide (NO) instead of nitrite, severely arresting post-germination growth and further seedling establishment
Summary
Plant growth is the result of the coordinated photosynthesis-mediated assimilation of oxidized forms of C, N and S. These reductive processes end primarily with the biosynthesis of amino acids and nucleotides, which allow the further synthesis of proteins and nucleic acids that is essential for plant growth and development. Ammonium is further incorporated to glutamate and glutamine through the plastidic glutamine synthetase/glutamate synthase (GS/GOGAT) cycle [5]. This reductive assimilatory pathway involves different subcellular locations as it begins in the cytoplasm but ends in chloroplasts. The balance between redox reactions catalyzed by NR and NiR seems crucial to determine the amount of NO that plants can produce and accumulate
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