Ildoo Hwang, Ph.D.

Associate Professor
Department of Life Science
Division of Molecular and Life Sciences
Plant Biochemistry

 
E-mail  ihwang@postech.ac.kr
Phone  054-279-2291
Laboratory  Development Signaling Network Lab.

Profile |  Research Interests  |  Selected Publications

Profile

Research Interests

Our main interests are to elucidate intracellular signal transduction pathways controlling plant growth and development, and to develop new tools for agricultural and environmental improvement. We are currently focused on the elucidation of cytokinin signal transduction mechanism in plants.

Cytokinins are essential plant hormones that are involved in the regulation of cell division, and diverse processes of plant growth and development. These processes include senescence, apical dominance, shoot meristem initiation, leaf and root differentiation, and chloroplast biogenesis. Cytokinins can reprogram terminally differentiated cells into stem cells and promote subsequent shoot regeneration indefinitely in cultured cells in combination with another phytohormone, auxin. Recent genetic and molecular studies in various plant species have suggested the involvement of two-component signaling proteins in cytokinin signal transduction.

Two-component systems - consisting of a histidine protein kinase that senses the input and a response regulator that mediates the output - control signal transduction pathways in many prokaryotes and in some eukaryotes (Fig. A, B). The signaling pathway is initiated when a histidine protein kinase sensor, modulated by an environmental cue, phosphorylates its own conserved histidine residue and transfers the phosphate to a conserved aspartate residue of a response regulator. In some cases, additional phosphotransfer steps may intervene between the histidine protein kinase and response regulator, mediated by a histidine phosphotransmitter.

The completion of the Arabidopsis genome sequence has revealed 54 genes encoding putative AHK, AHP and ARR proteins, suggesting an important involvement of the ancient and conserved signaling mechanism in many facets of plant cell regulation.

The development of the Arabidopsis protoplast system has enabled a functional genomic analysis of the two-component regulators, and deciphered a cytokinin signaling pathway in Arabidopsis. The pathway integrates multiple histidine protein kinase activities to common AHP proteins, which serve as cytoplasm/nuclear shuttles, and to distinct ARR proteins in the nucleus.

We use a combinational approach with genetic, genomic, and biochemical tools to elucidate the details in cytokinin perception, protein-protein interactions, and target gene expressions essential in cytokinin signaling. We will further determine how cytokinin, with a conserved short signaling circuitry, control cell division, and diverse processes of plant growth at different development stages.

Selected Publications 

1. Hass, C., Lohrmann, J., Albrecht, V., Sweere, U., Hummel, F., Yoo S.,, Hwang I., Zhu, T., Sch?er E.,, Kudla, J., and Harter K., 2004,  "The response regulator 2 mediates ethylene signalling and hormone signal integration in Arabidopsis", EMBO J, Vol.23(16), pp.3290-302 the European Molecular Biology Organization
2. Moore, B., Zhou, L., Rolland, F., Hall, Q., Cheng, W., Liu, Y., Hwang, I., Jones, T., and Sheen, J. Role, 2003, "of the Arabidopsis Glucose Sensor HXK1 in Nutrient, Light, and Hormonal Signaling", Science, Vol.300(#5617), pp.332-336
3. Hwang I, Chen HC, Sheen J, 2002, Two-component signal transduction pathways in Arabidopsis. Plant Physiol., 129(2):500-15.
4. Hwang I, Sheen J, 2001, Two-component circuitry in Arabidopsis cytokinin signal transduction. Nature. 413(6854):383-9.
5. Sze H, Liang F, Hwang I, Curran AC, Harper JF, 2000, Diversity and regulation of plant Ca2+ pumps: insights from expression in yeast. Annu Rev Plant Physiol Plant Mol Biol. 51:433-62.
6. Hwang I, Sze H, Harper JF, 2000, A calcium-dependent protein kinase can inhibit a calmodulin-stimulated Ca2+ pump (ACA2) located in the endoplasmic reticulum of Arabidopsis. Proc Natl Acad Sci U S A. 97(11):6224-9.
7. Curran AC, Hwang I, Corbin J, Martinez S, Rayle D, Sze H, Harper JF, 2000, Autoinhibition of a calmodulin-dependent calcium pump involves a structure in the stalk that connects the transmembrane domain to the ATPase catalytic domain. J Biol Chem. 275(39):30301-8.
8. Hwang I, Harper JF, Liang F, Sze H, 2000, Calmodulin activation of an endoplasmic reticulum-located calcium pump involves an interaction with the N-terminal autoinhibitory domain. Plant Physiol. 122(1):157-68.

Division of Molecular & Life Sciences| POSTECH