Molecular mechanism to prevent excessive uptake of an ammonium nutrient in rice

The writer: Toshihiko HAYAKAWA


Nitrogen is a major limiting nutrient in plant growth and productivity. In flooded paddy soils, wetland rice, an important mainstay crop, preferentially takes up ammonium as an abundant inorganic nitrogen source. However, an ammonium supply at high concentration is frequently toxic to many terrestrial plants. Therefore, ammonium influx into plant roots via the high-affinity transport system (HATS) is down-modulated under elevated external ammonium. HATS-responsible, plasma membrane-located ammonium transporter 1 (AMT1) proteins are inactivated via phosphorylation of the conserved threonine residue at the cytoplasmic carboxyl-tail under elevated external ammonium. We identified the role of a serine/threonine/tyrosine protein kinase, ACTPK1, in phosphorylation and inactivation of ammonium-induced AMT1;2 in ammonium-preferring rice grown under sufficient ammonium. This finding will help to improve nitrogen use efficiency in rice and confer ammonium-resistance on ammonium-sensitive plants. In this work, we collaborated with Dr. Mitsuhiro Obara, a principal investigator of the Japan International Research Center for Agricultural Sciences.

Marcel P. Beier*, Mitsuhiro Obara*, Akiko Taniai, Yuki Sawa, Jin Ishizawa, Haruki Yoshida, Narumi Tomita, Tsuyoshi Yamanaka, Yawara Ishizuka, Syuko Kudo, Akira Yoshinari, Shiho Takeuchi, Soichi Kojima, Tomoyuki Yamaya and Toshihiko Hayakawa (*equal contribution)

Lack of ACTPK1, an STY kinase, enhances ammonium uptake and use, and promotes growth of rice seedlings under sufficient external ammonium.
The Plant Journal, 93, 992-1006 (2018). doi: 10.1111/tpj.13824

Proposed model of ACTPK1-mediated down-modulation of ammonium uptake into rice roots under sufficient ammonium supply. ACTPK1, serine/threonine/tyrosine protein kinase; AMT, ammonium transporter; GS1, cytosolic glutamine synthetase 1; NADH-GOGAT1, NADH-glutamate synthase 1; and NH4+, ammonium.