Minisymposium 1: Mineral nutrition

Abs # 11005: Role of Nicotianamine and Deoxymugineic Acid in Plant Reproductive Development and Embryogenesis

Presenter:	Michiko, Takahashi , amichiko@mail.ecc.u-tokyo.ac.jp
Authors	Michiko, Takahashi  (A)   Haruhiko, Inoue  (A)   Yohei, Ushio  (A)   Hiromi, Nakanishi  (A)   Satoshi, Mori  (A)   Naoko, Nishizawa K (A) (B)
Affiliations:	(A): Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan (B): Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation, 332-0012 Saitama, Japan

Nicotianamine (NA), a chelator of various transition metals, is ubiquitously present in higher plants. NA is synthesized from three molecules of S-adenosylmethionine by nicotianamine synthase (NAS). In graminaceous plants, NA is the direct precursor of phytosiderophores that are secreted from the roots to solubilize ferric iron in the rhizosphere. Nicotianamine aminotransferase (NAAT) is the crucial enzyme in the biosynthetic pathway of mugineic acid family phytosiderophores (MAs), and its activity is induced in response to iron deficiency. NAAT activity has been only detected in graminaceous plants but not in dicot plants. To investigate the consequences of ectopic NAAT production in non-graminaceous plants, transgenic tobacco plants that overexpressed barley NAAT (naat-tobacco) was produced. The naat-tobacco developed a severe interveinal chlorosis in the young leaves and had Fe transport disorders. NA was not detected in these plants. Application of NA-Fe to the naat-tobacco reversed interveinal chlorosis. In addition, grafting of naat-tobacco onto transgenic tobacco overexpressing barley nicotianamine synthase gene (HvNAS1) (nas-tobacco) reversed the chlorosis, abnormal shaped inflorescence and sterility. NtNAS was expressed in inflorescence of wild type tobacco. These results suggested that NA was essential in the development of reproductive organs and seeds’ maturation (Takahashi et al., 2003, 15, 1263-1280, Plant Cell). Furthermore, to illuminate a role of NA in reproductive development in dicot plants, we investigated the expressions of four AtNAS in inflorescences and seeds of Arabidopsis using promoter:β-glucuronidase(GUS) analysis. All four AtNAS were expressed in reproductive organs. The expressions of AtNAS1, AtNAS3 and AtNAS4 were observed in developing embryo at early stage. The expressions of OsNAS and OsNAAT in inflorescences and seeds of rice were also examined. The expressions of OsNAS1, OsNAS3 and OsNAAT1 were marked, whereas OsNAS2 expression was very low. Their expressions were observed in endosperm, immature embryo, vascular tissue at the early stage of seed developing. In mature seeds, OsNAS1 was expressed especially in the endosperm and OsNAS3 and OsNAAT1 were expressed in the embryo. These results indicate that NA and DMA may play a critical role in embryogenesis besides a role in metal translocation to inflorescence and seeds.