OsARG is a key enzyme in Arg catabolism and plays a critical role during panicle development.
OsARG encodes an arginase in rice. Arginine is one of the main amino acids in nitrogen recycling and remobilization. In the case of rice, remobilized nitrogen from the vegetative organs accounts for 70-90% of the total panicle nitrogen.   The Arg concentration in leaves, roots and seeds varied from 0.4% to 3.4%, and abnormally high Arg levels ranging from 7.5 to 11.6% of total free amino acids, Arg which originate from the recycling of nitrogen, have been found in phloem sap. The difference in the Arg concentration of storage organs versus phloem sap in the reproductive stage is probably due to the activity of OsARG. Arg catabolism is well known for providing a significant portion of nitrogen during seedling development. Arginase, urease and its co-enzymes, and glutamine synthetases all play important roles in this pathway. Until now, only OsGS1;1 was found to exert an effect on panicle development in rice.  Under low exogenous nitrogen conditions, the panicle mainly utilized the nitrogen hydrolyzed from Arg catabolism; when exogenous nitrogen supplementation was increased, the pattern of nitrogen utilization in the panicles shifted to depend much more on exogenous nitrogen. The pathway that is used depends on the exogenous nutrition concentration, as described for nitrogen.
The rice narrow-grain and low-fertility mutant nglf-1 was derived from an anther culture of autotetraploid indica/japonica hybrid H3774 (H2088 × H891). Sequence comparison revealed a single nucleotide substitution resulting in a stop codon (TGA) in ORF8 of nglf-1. It has been verify that the mutation in OsARG is responsible for the nglf-1 phenotype. 
OsARG is expressed ubiquitously in all organs, including the root, stem, leaf blade, leaf sheath and panicle. Compared to WT, the expression in nglf-1 is reduced. The OsARG protein was localized in the mitochondria, consistent with other arginases. 
In the rice genome, OsARG is the only gene encoding arginase. A BLAST search with translated OsARG revealed that most plant arginases are encoded by one or two genes. OsARG has high identity with proteins from other organisms, including Arabidopsis thaliana,  Solanum lycopersicum,  Pinus taeda  and Glycine max.  OsARG also has high identity with arginases from five genera of monocotyledonous plants, including the arginases in Zea mays, Sorghum bicolor, Brachypodium distachyon, Triticum aestivum and Hordeum vulgare, all of which are members of the same clade, distinguishing them from all dicotyledonous species analyzed. The shared identity may indicate a different role in monocotyledonous plants than in dicotyledonous species. The OsARG protein comprises 340 residues with a predicted molecular mass of 36.96 kDa and pI of 5.90. Sequence alignment indicated a conserved arginase domain, and all plant arginases contain two His and four Asp residues that bind the Mn2+ co-factor.  A predicted mitochondrial targeting peptide is located at the N-terminal end, and this region showed the greatest diversity among various plant arginases. 
OsARG is a potential gene for improving rice nitrogen use efficiency.Improving nitrogen use efficiency is an important objective of breeding programs. In maize over-expressing the Gln1-3 gene, an increase in kernel number was observed under either high-nitrogen or low-nitrogen growth conditions.  A recent investigation of rice transformed with the cytosolic glutamine synthetase (GS1) gene indicated that, due to enhanced nitrogen use efficiency, lines over-expressing GS1 exhibited a 25–35% higher spikelet yield. The possibility of increasing OsARG expression, highlighting the potential use of manipulation of OsARG expression to improve rice yield under sub-optimal nitrogen conditions. However, extensive field experiments are needed. 
Labs working on this gene
1.National Key Facility for Crop Gene Resources and Genetic Improvement, Institute of Crop Science, Chinese Academy of Agricultural Sciences, Beijing, 100081, China
2.Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences, Beijing, 100081, China
3.National Key Laboratory for Crop Genetics and Germplasm Enhancement, Jiangsu Plant Gene Engineering Research Center, Nanjing Agricultural University, Nanjing, 210095, China
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