Increased iron efficiency in transgenic plants due to ectopic expression of nicotianamine synthase

Abstract

The plant-endogenous chelator for some metal micronutrients including iron, nicotianamine (NA), plays an important role in symplasmic and phloem transport of iron by keeping it in solution at cytoplasmic pH (Stephan and Scholz, 1996). Exogenous supply of NA for plants suffering from iron deficiency resulted in a re-greening by better iron distribution within the plants. The same was observed with the iron-accumulating tomato mutant chloronerva, the only plant we know to be NA-free. Thus, the enzyme NA synthase (NAS) was isolated from roots of barley grown under iron deficiency. The corresponding gene was cloned and successfully expressed in E. coli. Furthermore, NAS sequences were isolated from genomic DNA of tomato and A. thaliana. They were introduced by Agrobacterium in sense and antisense constructs in A. thaliana, tobacco and tomato. Tobacco sense lines overexpressing NAS from A. thaliana were selected based on significantly increased NA concentrations in the leaves compared to wild type plants. Plants of these lines grew faster, were green instead of chlorotic and exhibited a higher iron efficiency than wild type plants under iron limiting conditions. Crop plants with NAS overexpression thus could provide higher and more stable yield on areas of iron deficiency.