Inhibition of Sucrose Source-to-Sink Transport Reduces Iron Accumulation in Rice.

Iron is an essential element for plants growth and development. Biofortification has become an efficient way for iron accumulation in grains to enhance the nutritional quality of crops. Both iron and sucrose are transported via phloem during grain filling in rice. However, the relationship between iron and sucrose transport remains unclear. In this study, we aimed to elucidate the relationship between sucrose transport and iron accumulation in rice. We first found that the efficient iron accumulated stage and sucrose unloading stage overlapped at 5–10 DAF during grain filling. The close relationship was further validated by transgenic lines (Y2 and Y6) overexpressing yeast (Y) invertase (INV). The sucrose efflux rate in phloem decreased by 40.1% and 30.6%, and the iron efflux rate in phloem was also reduced by 73.7% and 51.0% in Y2 and Y6, respectively. Thus, the iron content in grains was decreased. The transcriptome analysis on grains of WT and Y2 at 10 DAF was used to compare the difference in carbohydrate and iron metabolism. Seven upregulated DEGs and twenty-four downregulated DEGs related to carbohydrate metabolism were identified in Y2. The expression levels of starch synthesis and sugar transport genes in Y2 were lower than those in WT. The expression levels of iron-related genes, including OsTOM1, OsNAS1, OsNAS2, OsIRT1, OsYSL9, and OsOPT7, were significantly downregulated in Y2. These results indicated that blocking photoassimilates allocation between source and sink reduces iron accumulation in grains. [ABSTRACT FROM AUTHOR]