Novel rice iron biofortification approaches using expression of ZmYS1 and OsTOM1 controlled by tissue-specific promoters

Intrinsic improvement of iron (Fe) concentration in rice grains, called rice Fe biofortification, is a promising countermeasure against widespread human Fe deficiency. In this study, two novel rice Fe biofortification approaches are reported. The first approach (Y approach) involved the expression of maize YELLOW STRIPE 1 controlled by the HEAVY METAL ATPASE 2 promoter. The Y approach increased the polished grain Fe concentrations up to 4.8-fold compared with the non-transgenic (NT) line. The second approach (T approach) involved the expression of rice TRANSPORTER OF MUGINEIC ACID 1 controlled by the FERRIC REDUCTASE DEFECTIVE LIKE 1 promoter. The T approach increased the polished grain Fe concentrations by up to 3.2-fold. No synergistic increases in the polished grain Fe concentrations were observed when Y and T approaches were combined (YT approach). However, the polished grain Fe concentrations further increased by 5.1- to 9.3-fold compared with the NT line, when YT approach was combined with the endosperm-specific expression of FERRITIN (YTF approach), or when YTF approach was combined with the constitutive expression of NICOTIANAMINE SYNTHASE (YTFN approach). Total grain weight per plant in most Y, T, YT, and YTFN lines was comparable to that in the NT line, while it was significantly decreased in most YTF lines. The novel approaches reported in this study expand the portfolio of genetic engineering strategies that can be used for Fe biofortification in rice.