Molecular analysis of nicotianamine synthesis in Strategy I and II plants

Abstract

Nicotianamine (NA) is an intermediate in the biosynthetic pathway of the mugineic acid-family phytosiderophores (MAs), which are crucial components of the iron acquisition of graminaceous (Strategy II) plants. In non-graminaceous (Strategy I ) plants, NA is thought to be an essential chelator for metal cation homeostasis. Nicotianamine synthase (NAS, EC 2.5.1.43) catalyzes the trimerization of S-adenosylmethionine (SAM) to form one molecule of NA. We isolated seven barley cDNA clones (hvnas1- hvnas7), a genomic fragment containing HvNAS1 from barley and three rice cDNA clones (osnas 1- osnas 3), a genomic fragment containing both OsNAS1 and OsNAS2 from rice. We also isolated three Arabidopsis cDNA clones (atnas 1-atnas3). We introduced barley genomic DNA fragments containing HvNAS1 with either 9 or 2 kb of the 5′-flanking region into rice, using Agrobacterium-mediated transformation. Fe deficiency induced HvNAS1 expression in both the roots and leaves of the transgenic rice, as occurs with rice NAS genes.