Zinc Transport in Rice: Dilemma between optimal plant requirement and human nutrition.

Zinc (Zn) is an essential micronutrient for both plants and animals, while Zn deficiency in crops and humans is a global problem affecting crop productivity and human health. Since plants and humans differ in their Zn requirement, there is a dilemma between plant nutrition and human nutrition. In this review, we focus on the transport system of Zn from soil to grain in rice (Oryza sativa), which is a major dietary source of Zn for people subsiding on rice-based diets. We describe transporters belonging to different family, which are involved in the uptake, vacuolar sequestration, root-to-shoot translocation and distribution of Zn. We also discuss the possible regulation mechanism of these transporters. Several examples are given on enhancing Zn accumulation and bioavailability in rice grains through manipulation of genes highly expressed in the nodes, where Zn is highly deposited. We finally provide our perspectives toward breeding rice cultivars with both increased tolerance to Zn-deficiency stress and high Zn density in rice grains.