The Roles of NRT1 Transporters in Nitrate Transport and Signaling
Nitrogen fertilizer is essential to increase crop yield. But, production of N fertilizer consumes 1% of world energy, and poses the highest input cost for many crops. Nevertheless, only 30% to 50% of N fertilizer applied can be utilized by crops, and the remainder leads to production of greenhouse gas or eutrophication of rivers and oceans. For most plants, nitrate is the primary nitrogen source. In order to find new strategy to enhance nitrogen utilization efficiency, we took several approaches to understand how nitrate is uptaken, translocated and sensed in plants.
Nitrate concentrations in the soil can vary in four orders of magnitude, ranging from uM to mM. To cope with such fluctuating situations, plant has evolved several strategies including multiple uptake systems, efficient nitrate allocation, and delicate sensing mechanisms. Study of NRT1 transporters in Arabidopsis helps us to understand how plants survive under N deficiency and N superabundance. Young developing leaves demand higher levels of nutrients, but acquire less nutrients from xylem stream due to low transpiration rate. In N deficient condition, nitrate transporter NRT1.7, expressed in the phloem of the minor vein of the old leaves, help to retrieve excess nitrate stored in the old leaves to feed young developing leaves. While in high nitrate condition, NRT1.11/12, expressed in the phloem of the petiole of full-size leave, mediate xylem to phloem transfer of nitrate to feed young leaves. These studies indicated that plants use different strategies to fulfill the high nutrient demand of the young developing leaves under nitrate sufficient or deficient conditions.
Dr. Yi-Fang Tsay
- Research Fellow, Institute of Molecular Biology, Academia Sinica, Taiwan
- Coordinator, Taiwan International Graduate Program in Molecular and Cell Biology (MCB)