Iron (Fe) is an essential element for both plant growth and human health. However, its availability in soils, particularly in alkaline conditions, is often limited. Rice (Oryza sativa) uniquely utilizes a combination of two iron uptake strategies: Strategy I and Strategy II. The specific roles of the transporters OsIRT1 and OsIRT2 within Strategy I have remained elusive due to the absence of suitable mutants.

In a study published in Plant Physiology and Biochemistry, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences identified the pivotal role of two specific genes, OsIRT1 and OsIRT2, in the process of iron uptake in rice plants, and revealed that this form of iron is the most accessible in the flooded paddies that characterize these plants' typical growing environment.

By employing CRISPR-Cas9 gene editing technology, researchers generated loss-of-function mutants for OsIRT1 and OsIRT2 separately and in combination. They then investigated the impact of these proteins on the symptoms of Arabidopsis Atirt1 deficiency through transgenic experiments.

Researchers found that OsIRT1 and OsIRT2 played important roles in Fe(II) uptake by rice, especially under iron deficiency conditions. The shoot and seed iron concentrations were significantly decreased in the mutant plants compared to the wild-type rice; however, this was only under conditions where soluble ferrous iron (Fe(II)), which is abundant in flooded rice fields, was available. This finding indicated that OsIRT1 and OsIRT2 are indispensable for Fe(II) uptake.

Moreover, researchers found that the transcription factor OsPRI1, a member of the OsbHLH IVc family, directly bound to and activated the promoters of both OsIRT1 and OsIRT2 in conditions of iron scarcity. Both OsIRT1 and OsIRT2 successfully alleviated iron-deficiency symptoms in a well-documented Arabidopsis mutant devoid of its native IRT1 transporter, verifying their functional competence in iron assimilation.

"We have verified that OsIRT1 and OsIRT2 serve as the principal gatekeepers for the absorption of essential ferrous iron in rice paddies. Their disruption leads to a decrease in the iron content within the grain," said LIANG Gang from XTBG.