Over-expression of the MxIRT1 Gene Increases Iron and Zinc Content in Rice Seeds

Iron and zinc are essential in plant and human nutrition. Iron deficiency has been one of the causes of human mortality, especially in developing countries with high rice consumption. MxIRT1 is a ferrous transporter that has been screened from an iron-efficient genotype of the apple tree, Malus xiaojinensis Cheng et Jiang. In order to produce Fe-biofortified rice with MxIRT1 to solve the Fe-deficiency problem, plant expression vectors of pCAMBIA1302-MxIRT1:GFP and pCAMBIA1302-anti MxIRT1:GFP were constructed that led to successful production of transgenic rice. The transgenic plant phenotypes showed that the expression of endogenous OsIRT1 was suppressed by anti-MxIRT1 in antisense lines that acted as an opposing control, while sense lines had a higher tolerance under Zn- and Fe-deficient conditions. The iron and zinc concentration in T3 seeds increased by three times in sense lines when compared to the wild type. To understand the MxIRT1 cadmium uptake, the MxIRT1 cadmium absorption trait was compared with AtIRT1 and OsIRT1 in transgenic rice protoplasts, and it was found that MxIRT1 had the lowest Cd uptake capacity. MxIRT1 transgenic tobacco-cultured bright yellow-2 (BY-2) cells and rice lines were subjected to different Fe conditions and the results from the non-invasive micro-test technique showed that iron was actively transported compared to cadmium as long as iron was readily available in the environment. This suggests that MxIRT1 is a good candidate gene for plant Fe and Zn biofortification.