Professor Youngsook Lee (Division of Integrative Biology and Biotechnology) and her team have found a transporter carrying abscisic acid (ABA), a stress hormone, synthesized in plants undergoing stresses like extreme climate or salinity. Their results integrate ABA dependent signaling and transport processes, and it is expected to open a new venture for the engineering of drought-tolerant plants.

They have succeeded to find the existence of transporter ABCG40 that can transport ABA, a hormone known to be produced in responses to environmental stress such as extreme temperatures, high salinity, or drought and plant pathogens. In both animals and plants, hormones are known to play essential roles in the regulation of growth, development, and environmental response, and they are circulated throughout the organism in part by the extracellular fluid. Plant hormones are known to be transported over long distances, such as auxin and ABA. These two are weak acids, and thus, they exist in either protonated, uncharged or in anionic forms depending on the prevailing pH. In drought condition, the pH of plant extracellular fluid increase. Therefore, for effective transportation of anionic forms ABA into the cells, plant needs protein carriers.

For ABA to be able to protect a plant, it should be imported inside of the plant cell, but no transporter has been identified before. The ABCG40 proteins that absorb ABA quickly into cells, and it activates stress-tolerant genes inside cells. Drought-stress experiments provided further evidence that AtABCG40 is integral to stress tolerance. Plants were grown for 2 weeks under standard conditions, and water is subsequently withheld. Leaves of the two mutant lines (abcg40-1, abcg40-2) withered faster than those of the wild-type (WT) plants (see figure A).

Stomata of abcg40 plants are less sensitive to ABA. In figure B, the delayed elevation of leaf temperature after ABA treatment of abcg40 plants was compared with wild-type (WT). Leaf temperature was monitored using an Infrared Thermal Imaging Camera.

Considering the fact that the rapid adjustment to a stress, such as drought stress, is a prerequisite for plant survival, these results have significant potential to further applications. “This finding of uptake process of ABA and the crucial role of the transporter ACBG40 may help develop a plant that is adaptable to the extreme conditions of environmental stresses,” Professor Lee commented.

Professor Enrico Martinoia, a renowned professor in the field of plant ABC transporters from Switzerland, has participated in this research. The results are published on the January 18 issue of Proceedings of National Academy of Science of USA (PNAS). This research is supported by the Ministry of Education, Science and Technology, and National Research Foundation of Korea.