Enhancing tolerance of rice to alkaline soils using genes involved in Fe acquisition in plants.

One of the widest ranging abiotic stresses in world agriculture arises from low iron (Fe) availability due to high soil pH, with 30% of arable land too alkaline for optimal crop production. To aquire Fe, Graminaceous plants use a chelation strategy and release phytosiderophores from their roots to chelate Fe (III) in the soil. Non-graminaceous plants differ from graminaceous plants in acquiring Fe, ferric reduction on root surface being the first step of iron uptake. Rice is very susceptible to low Fe availability. We enhanced the tolerance of rice to Fe deficiency in calcareous soils by introducing the barley genes participating in the phytosiderophore synthesis and tested these transgenic rice lines in a field experiment on a calcareous soil under paddy conditions. We showed that introducing barley genes involved in the synthesis of phytosiderophore into rice is an effective, practical method to improve agricultural productivity in calcareous soils. We also improved the tolerance of rice to Fe deficiency by increasing the ferric reductase activity of root cells by introducing the engineered gene refre1-372. To understand the molecular mechanisms that regulate Fe acquisition in plants, we analyzed the promoter region of the barley Fe deficiency inducible IDS2 gene and identified two novel cis-acting elements, IDE1 and IDE2. We identified two rice transcription factors, IDEF1 and IDEF2, which specifically bind to IDE1 and IDE2, respectively. The enhanced expression of transcription factors resulted in increased phytosiderophore secretion and tolerance to low Fe availability in a calcareous soil.