Manipulating phloem iron transport using the phloem-specific promoter OsSUT1 enhances grain iron accumulation in rice

Human diets are commonly deficient in iron. Hence, increasing the iron content in rice, a major staple crop globally, will help overcome this iron deficiency. The phloem is an important route for iron distribution. However, little is known about the effects of manipulating iron transport in the phloem on iron content. The phloem-specific OsSUT1 promoter is used to drive the expression of iron transport genes OsYSL9 and OsIRT1. The phloem exudate iron content, iron harvest index and remobilization contribution rate are enhanced in pOsSUT1::OsYSL9 (SY) and pOsSUT1::OsIRT1 (SI) transgenic lines. The iron content of brown rice in SY and SI lines is increased by 1.27- and 1.36-fold, respectively. The iron content of milled rice is also increased by 1.44- and 1.60-fold, respectively. The grain weight of SY and SI lines is higher than that of wild type. Furthermore, the chalky rice rate and chalkiness degree are significantly decreased in the SY and SI lines due to a longer active grain-filling period. Overexpression of iron transport genes under the control of the phloem-specific promoter can increase the iron content in grains and also improve the milling and appearance quality of rice.