Nicotianamine synthases regulate the biosynthesis of two mineral chelators key for rice grain biofortification, nicotianamine (NA) and 2′-deoxymugineic acid (DMA). We produced transgenic rice expressing OsNAS2 under the OsRCc3 promoter (RcN2) and mutated OsLpa1 in these (lpa1 RcN2) and the wild-type (lpa1) to enhance essential mineral accumulation in grains while lowering phytic acid (PA) levels. NA and DMA contents were higher in the brown grains of RcN2, lpa1 RcN2, and lpa1 plants. The grains of these lines accumulated increased levels of essential minerals, with lpa1 RcN2 exhibiting the greatest increases. PA-bound iron and zinc levels were lower in lpa1 and lpa1 RcN2 grains, while NA- and DMA-bound iron and zinc levels were higher in RcN2, lpa1 RcN2, and lpa1 grains. Field-grown RcN2 plants showed no significant growth penalties, unlike lpa1 and lpa1 RcN2. Furthermore, lpa1 and lpa1 RcN2 grains were chalky, a property that facilitates rice flour production.
Rahman et al. (Wed,) studied this question.