Climate change caused by increasing atmospheric CO2 is a major environmental problem of the 21st century. There has been much discussion about how to reduce CO2 output and prevent global warming. In this respect, plants are an important part of the overall picture as they are primary CO2 consumers and are directly challenged by increasing CO2 levels. Moreover, plants vary in their responses to elevated CO2. Plants that adapt better to this change are expected to out-compete their neighbors, which would cause instability in present ecosystems and unpredictable changes in weather and climate.

In plants, CO2 uptake and water release occur through stomata. Stomata are formed by a pair of highly specialized epidermal cells, termed guard cells, and their opening and closing must be tightly controlled for optimal plant performance. It has been known for a long time that guard cells respond to high CO2 by closing their stomata. However, only recently have the molecular and cellular mechanisms for sensing and responding to high CO2 concentrations begun to be understood. CO2 is now known to have a direct effect on guard cells and to elicit stomatal closing through complex molecular interactions between currently ill-defined positive and negative factors.

Our research into the role of ABC transporters in guard cell regulation resulted in the identification of an ABCB-type ABC transporter that is strongly expressed in guard cells and localized at the plasma membrane. We observed in intact leaves that, under elevated CO2 conditions, deletion mutants of AtABCB14 closed their stomata more rapidly than their wild-type counterparts, whereas AtABCB14-overexpressing mutants closed their stomata only partially. Further detailed analyses using E. coli and HeLa cell revealed that AtABCB14 plays a role as a malate importer. Thus, we conclude that AtABCB14 negatively regulates stomatal movement by transporting malate into the guard cell under elevated CO2 condition.

These results are entirely novel and have strong implications for our current knowledge about the regulation of pore size under high CO2 condition. A topic that has not alone major repercussions for basic plant science but also for agriculture, especially within the perspective of rising atmospheric CO2 concentrations and the need to assure adequate food production for future generations.

In addition, these results are very exciting for the broad and diverse ABC transporter community which is composed of scientists studying ABC transporters in all kingdoms of life, from prokaryotes to human. According to the reports up to now, ABC proteins of the same sub-family have similar functions and their functions are conserved between organisms also. In fact, many functional studies of genes were performed using homology with already identified genes. Thus, our studies may be helpful for identifying unknown roles of ABC proteins, and provide clues to solve the functions of animal ABC proteins for which the mutants are difficult to obtain.

Professor Youngsook Lee
Department of Life Science
Tel: +82-54-279-8185
Fax: +82-54-279-2199
Email: ylee@postech.ac.kr

Dr. Miyoung Lee
Department of Life Science
Tel: +82-54-279-5980
Fax: +82-54-279-2199
E-mail: anny98@postech.ac.kr