What are you aiming to achieve?

Plants grow by taking in minerals via their roots from the soil. We are aiming to explain the mechanism by which plants control their mineral uptake. The main role in mineral uptake is played by a group of proteins known as transporters. Transporters are buried in the cell membranes, and function by promoting the permeation of substances through the membranes. We have discovered two types of transporters for boron, a mineral necessary to plants.

Fig. 1 Position of two types of boron transporters in the epidermal cells of the root of Arabidopsis thaliana

Figure 1 shows these transporters visualized by fusing them to fluorescent proteins. Epidermal cells in the root of Arabidopsis thaliana plant contain a transporter known as NIP5;1 (mCherry-NIP5;1: red), which is present on the cell membrane on the side that faces the soil, and takes boron into the cell interior, while a transporter known as BOR1 (BOR1-GFP: green), which works to export boron from the cells to the exterior, is present on the cellular membrane on the side facing the stele. As a result, boron from the soil is taken into cells by NIP5;1, and exported in the direction of the stele by BOR1. It is important for transporters to be positioned in appropriate places in order to transport a mineral in a specific direction. We are researching the mechanism by which transporters are unevenly distributed within the cell membranes.

We have also discovered that the boron transporter BOR1 is eliminated from the cellular membrane, and decomposes, if the concentration of boron in the environment rises (Fig. 2). The cell decomposes the transporter if it becomes unnecessary or starts to get in the way. We are looking into how the plant detects the concentration of minerals and goes on to control the quantity of transporters.

 

What sort of organisms do you use, and in what type of experiments?

Fig. 2 Degradation of boron transporters in the root of Arabidopsis thaliana

Our research is mainly centered on the Arabidopsis thaliana plant, which is known as a model plant. Arabidopsis thaliana is not a crop, but it is genetically suited as a perfect subject for research and shares common molecular aspects with many plants. We also use E. coli and budding yeasts in the course of our research.

We use genetic methods in order to look at the mechanisms behind plant cells detecting mineral concentrations, and controlling transporter positions and quantities. By looking at how the positioning or quantity of a transporter changes if a particular genetic function is missing or altered, we can understand the role of that particular gene.

In order to be able to “look at” the position of transporters in plants, we fuse the transporters to fluorescent proteins such as GFP (green fluorescent protein) and mCherry (a type of red fluorescent protein). We use transformation technology to introduce these proteins into the plant, and then use a fluorescence microscope to observe them in living form. As in Figure 1, we are able to see the position of multiple proteins by observing the different colored fluorescent proteins at the same time, and we can trace changes in real time.

 

How does this contribute to agriculture?

The surrounding mineral environment is important for the development of plants. Due to mineral concentrations being too low or too high, roughly 70% of the world’s arable land is covered by what is known as “problem soil”, which results in low crop yields. Plants are, however, able to grow even with a certain amount of variation in mineral quantity. One way of dealing with this is thought to be by detecting the concentration of minerals and then controlling the position and quantity of transporters in response. We are aiming to understand this intrinsic mechanism within plants, and apply it to other areas. If we can increase the innate ability of a particular crop, or transfer it to another crop, it may become possible to grow them in problem soil. We have succeeded in creating an Arabidopsis thaliana that grows well in low boron environments by increasing its quantity of boron transporters. In the future, by understanding more detail about the mechanism of transporter control, we will be able to create plants that grow well in a wide range of mineral environments, and connect this with applications that would allow plants to store minerals in specific tissue.