Optimisation of nutrient transport processes by plants -boron transport as an example

摘要

Boron is an essential micronutrient for plants and is also toxic in high concentrations. In a number of countries, boron deficiency and toxicity hamper agricultural production. One of the strategies to overcome the problem is to improve boron transport/utilization properties of crop plants. For this it is important to understand boron transport mechanisms at the molecular level. Boron transporters were not known until several years ago. We identified BOR1 as the first boron transporter required for efficient xylem loading of boron (B). Arabidopsis and rice have seven and four BOR1 or BORl-like genes, all likely to encode efflux transporters, with different physiological functions and location within the cell. We also identified NIP5;1, a protein similar to aquaporin, as a transporter required for efficient B uptake. Expression of B0R1 and NIP5;1 is both upregulated under B deficient conditions but with different mechanisms. BOR1 accumulates in plasma membrane under low B conditions, and degraded through endocytosis under sufficient B supply. NIP5;1 is transcriptionally upregulated under low B conditions. Recently we have been successful in generating transgenic plants that are tolerant to low or high boron. In rice, OsBORl is required for efficient boron uptake and growth under B-limitation.