Constitutive expression of a barley Fe phytosiderophore transporter increases alkaline soil tolerance and results in iron partitioning between vegetative and storage tissues under stress

Cereals have evolved chelation systems to mobilize insoluble iron in the soil, but in rice this process is rather inefficient, making the crop highly susceptible to alkaline soils. We therefore engineered rice to express the barley iron-phytosiderophore transporter (HvYS1), which enables barley plants to take up iron from alkaline soils. A representative transgenic rice line was grown in standard (pH 5.5) or alkaline soil (pH 8.5) to evaluate alkaline tolerance and iron mobilization. Transgenic plants developed secondary tillers and set seeds when grown in standard soil although iron concentration remained similar in leaves and seeds compared to wild type. However, when grown in alkaline soil transgenic plants exhibited enhanced growth, yield and iron concentration in leaves compared to the wild type plants which were severely stunted. Transgenic plants took up iron more efficiently from alkaline soil compared to wild type, indicating an enhanced capacity to increase iron mobility ex situ. Interestingly, all the additional iron accumulated in vegetative tissues, i.e. there was no difference in iron concentration in the seeds of wild type and transgenic plants. Our data suggest that iron uptake from the rhizosphere can be enhanced through expression of HvYS1 and confirm the operation of a partitioning mechanism that diverts iron to leaves rather than seeds, under stress.