AUTHOR=Fujita Takayuki , Beier Marcel Pascal , Tabuchi-Kobayashi Mayumi , Hayatsu Yoshitaka , Nakamura Haruka , Umetsu-Ohashi Toshiko , Sasaki Kazuhiro , Ishiyama Keiki , Murozuka Emiko , Kojima Mikiko , Sakakibara Hitoshi , Sawa Yuki , Miyao Akio , Hayakawa Toshihiko , Yamaya Tomoyuki , Kojima Soichi TITLE=Cytosolic Glutamine Synthetase GS1;3 Is Involved in Rice Grain Ripening and Germination JOURNAL=Frontiers in Plant Science VOLUME=13 YEAR=2022 URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.835835 DOI=10.3389/fpls.2022.835835 ISSN=1664-462X ABSTRACT=

Ammonium is combined with glutamate to form glutamine. This reaction is catalyzed by glutamine synthetase (GS or GLN). Plants harbor several isoforms of cytosolic GS (GS1). Rice GS1;3 is highly expressed in seeds during grain filling and germination, suggesting a unique role in these processes. This study aimed to investigate the role of GS1;3 for rice growth and yield. Tos17 insertion lines for GS1;3 were isolated, and the nitrogen (N), amino acid, and ammonium contents of GS1;3 mutant grains were compared to wild-type grains. The spatiotemporal expression of GS1;3 and the growth and yield of rice plants were evaluated in hydroponic culture and the paddy field. Additionally, the stable isotope of N was used to trace the foliar N flux during grain filling. Results showed that the loss of GS1;3 retarded seed germination. Seeds of GS1;3 mutants accumulated glutamate but did not show a marked change in the level of phytohormones. The expression of GS1;3 was detected at the beginning of germination, with limited promoter activity in seeds. GS1;3 mutants showed a considerably decreased ripening ratio and decreased N efflux in the 12th leaf blade under N deficient conditions. The β-glucuronidase gene expression under control of the GS1;3 promoter was detected in the vascular tissue and aleurone cell layer of developing grains. These data suggest unique physiological roles of GS1;3 in the early stage of seed germination and grain filling under N deficient conditions in rice.