Abstract
Asparagine is one of the important amino acids for long-distance transport of nitrogen (N) in plants. However, little is known about the effect of asparagine on plant development, especially in crops. Here, a new T-DNA insertion mutant, asparagine synthetase 1 (asn1), was isolated and showed a different plant height, root length, and tiller number compared with wild type (WT). In asn1, the amount of asparagine decreased sharply while the total nitrogen (N) absorption was not influenced. In later stages, asn1 showed reduced tiller number, which resulted in suppressed tiller bud outgrowth. The relative expression of many genes involved in the asparagine metabolic pathways declined in accordance with the decreased amino acid concentration. The CRISPR/Cas9 mutant lines of OsASN1 showed similar phenotype with asn1. These results suggest that OsASN1 is involved in the regulation of rice development and is specific for tiller outgrowth.
Highlights
Nitrogen (N) is one of the most important macro nutrients for plant growth and development
One line that has an insertion in the fourth intron of asparagine synthetase 1 (ASN1) showed strong growth defects compared with wild type (WT) (Figure 1a,b)
The T-DNA insertion mutant of OsASN1 was analyzed in detail, and CRISPR/Cas9 lines of this gene were constructed to confirm the phenotype
Summary
Nitrogen (N) is one of the most important macro nutrients for plant growth and development. N is absorbed by plant roots mainly in two forms: ammonium and nitrate. Some of the nitrate is directly used by root, and some is reduced to ammonium. Ammonium was assimilated to glutamine by glutamine synthetase and glutamine-2-oxoglutarate aminotransferase and transported to the shoot. Some of the glutamine could be synthesized to asparagine and other amino acids or other compounds containing N [1]. The most important forms of N transport from root to shoot is glutamine and asparagine. In rice xylem and phloem sap, glutamine is the most abundant amino acid for N transportation, the second is asparagine [2,3]. GS2, which is localized in mitochondria or chloroplast, is related to the ammonia assimilation from nitrate reduction or photorespiration [9,10]
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