Original Research ARTICLE
Nicotianamine synthesis by OsNAS3 is important for mitigating iron excess stress in rice
- 1Ishikawa Prefectural University, Japan
- 2Akita Prefectural University, Japan
- 3Meiji Gakuin University, Japan
- 4The University of Tokyo, Japan
- 5Graduate School of Biotechnology, Kyung Hee University, South Korea
Iron (Fe) toxicity in plants causes tissue damage and cellular homeostasis disorders, thereby affecting plant growth and development. Nicotianamine (NA) is a ubiquitous chelator of metal cations and is responsible for metal homeostasis. In rice, it is synthesized by three NA synthase (NAS) genes, of which the expression of OsNAS1 and OsNAS2 but not of OsNAS3 is strongly induced in response to Fe deficiency. Recently, we found that OsNAS3 expression is strongly induced with excess Fe in most rice tissues, particularly old leaves, suggesting that it may play a vital role under excess Fe conditions. However, how OsNAS3 participates a role in response to excess Fe in rice remains poorly understood. In this study, we clarified the physiological response of OsNAS3 expression to excess Fe and the role of NA synthesis in this condition. Promoter GUS analyses revealed that OsNAS3 was widely expressed in roots, especially in vascular bundle, epidermis, exodermis, stem, and old leaf tissues under Fe excess compared to control plants. NA and deoxymugineic acid (DMA; a type of phytosiderophore synthesized by Strategy II species) were present in both roots and shoots under Fe excess likewise under control conditions. In addition, OsNAS3 knockout plants were sensitive to excess Fe, exhibiting inferior growth, more severe leaf bronzing, and greater Fe accumulation than non-transformants with excess Fe. Moreover, the knockout plants accumulated more Fe in their leaves than non-transformants. We also observed that NA-overproducing rice was tolerant to excess Fe. Overall, these findings suggest that rice synthesizes NA with OsNAS3 under Fe excess in roots and shoots, and that NA and DMA within the plant body are important for mitigating excess Fe stress and alleviating other metal deficiencies in rice. This report will be important for the development of tolerant rice adapted to Fe-contaminated soils.
Keywords: Iron excess, iron toxicity, rice, OsNAS3, Nicotianamine, deoxymugienic acid, detoxification
Received: 31 Jan 2019;
Accepted: 02 May 2019.
Edited by:Wolfgang Schmidt, Academia Sinica, Taiwan
Reviewed by:Elsbeth L. Walker, University of Massachusetts Amherst, United States
Alexander A. Johnson, The University of Melbourne, Australia
Copyright: © 2019 Aung, Masuda, Nozoye, Kobayashi, Jeon, An and Nishizawa. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Prof. Naoko K. Nishizawa, Ishikawa Prefectural University, Nonoichi, 760-8521, Ishikawa, Japan, email@example.com