Involvement of auxin in the regulation of ammonium tolerance in rice (Oryza sativa L.)
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Background and aims
Ammonium (NH4+) is an important nitrogen source and is widely used as a fertilizer in agricultural systems. However, excess NH4+ inhibits root growth, and, subsequently, vegetative shoot growth and yield. This study examines whether auxin is involved in differential NH4+ tolerance in rice (Oryza sativa L.), and how auxin is regulated under high-NH4+ conditions in rice.
An NH4+-sensitive (Kasalath, Kas) and an NH4+-insensitive (Koshihikari, Kos) rive cultivar were cultured hydroponically with or without exogenous indole-3-acetic acid (IAA) and auxin biosynthesis inhibitors. Root growth, root area, tissue IAA content, and transcription of genes involved in auxin biosynthesis, conjugation and degradation were determined.
pDR5::GUS staining and auxin measurement show that high NH4+ can decrease free IAA content in roots. In addition, quantitative RT-PCR, pharmacology, and genetics analysis suggest that Kos possesses a higher capacity for auxin biosynthesis and a weaker capacity for auxin metabolism compared to Kas under high-NH4+ stress.
We conclude that the NH4+-tolerant cultivar possesses a higher capacity to maintain auxin homeostasis under high-NH4+ stress, and that this advantage is incurred by promotion of auxin biosynthesis and a suppression of auxin metabolism.
KeywordsAmmonium toxicity Auxin level Nitrogen fertilizer Rice Root development
Dioxygenase for Auxin Oxidation
Group II GRETCHEN HAGEN3 acyl amido synthetases
TRYPTOPHAN AMINOTRANSFERASE RELATED
5-(4-chlorophenyl)-4H-1, 2, 4-triazole-3-thiol
We thank Prof. Shiping Wang (Huazhong Agricultural University) and Prof. Jianmin Wan (Nanjing Agricultural University) for kindly providing the OsGH3.2ox and Osdao mutant, respectively. This work was supported by grants from the National Natural Science Foundation of China [31430095, 31601823 and 31471948.], China Postdoctoral Science Foundation [2015 M58048 and 2017 T100411] and the University of Melbourne.
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