Identification of a vacuolar glutamine efflux transporter in rice

The writer: Toshihiko Hayakawa

Nitrogen is a major limiting nutrient in plant growth and productivity. In flooded paddy soils, wetland rice (Oryza sativa L.), an important mainstay crop, preferentially takes up ammonium as an abundant inorganic nitrogen source. Glutamine is a product of ammonium assimilation catalyzed by glutamine synthetase and glutamate synthase. The growth of paddy rice depends on root ammonium assimilation and subsequent root-to-shoot allocation of glutamine; however, little is known about the mechanism of glutamine storage in roots. The rice amino acid transporter-like 6 (OsATL6) is a member of the ATLa/AVT6 subfamily of plant amino acid transporters whose functions remain unknown. In this study, we revealed the role of OsATL6 in exporting ammonium-derived glutamine from the cytosol into the vacuole for temporary vacuolar storage of excess glutamine, thereby influencing the root-to-shoot allocation of glutamine and the subsequent growth of rice seedlings under ammonium replete conditions. This finding will help to improve nitrogen use efficiency and growth of rice for achieving more productive and sustainable agriculture towards SDGs (Target 2.4). In this work, we collaborated with Dr. Kuni Sueyoshi, Faculty of Agriculture, Niigata University; Drs. Kentaro Tanemura and Yuki Hiradate, Animal Reproduction and Development, Graduate School of Agricultural Science, Tohoku University; Drs. Nobuyuki Uozumi and Shunya Saito, Biomolecular Engineering, Graduate School of Engineering, Tohoku University; and Dr. Mitsuhiro Obara, the Japan International Research Center for Agricultural Sciences.

These results have been published in Online Version of Record (July 21, 2021) before inclusion in an issue of The Plant Journal.

Saori Ogasawara*, Masataka Ezaki*, Ryusuke Ishida, Kuni Sueyoshi, Shunya Saito, Yuki Hiradate, Toru Kudo, Mitsuhiro Obara, Soichi Kojima, Nobuyuki Uozumi, Kentaro Tanemura, and Toshihiko Hayakawa** (*equal contribution, **corresponding author)
Rice amino acid transporter-like 6 (OsATL6) is involved in amino acid homeostasis by modulating the vacuolar storage of glutamine in roots.
The Plant Journal,107, 1616-1630 (2021)

Proposed model of the putative role of OsATL6 in the temporary storage of excess glutamine in root vacuoles of rice seedlings under replete ammonium supply. (A) Wild-type rice. (B) ATL6-knockdown rice. NH4+, ammonium; AMT1, ammonium transporter 1; ATL6, amino acid transporter-like 6; Gln, glutamine; Glu, glutamate; GS1, cytosolic glutamine synthetase 1; NADH-GOGAT1, NADH-glutamate synthase 1; and 2-OG, 2-oxoglutarate.

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