Research Area

 1. Symbiotic Nitrogen Fixation

A] An actinomycete, Frankia, participate in symbiotic associations with variety of woody plants such as Alnus and Elaeagnus. The host plants have been used in forestry and land reclamation due to nitrogen-fixing ability of their root nodules. Although many Frankia strains are available, there have been few studies on their molecular genetics mainly due to their slow growth rate and lack of transformation system. We isolated symbiont Frankia sp. EuIK1, EuIK2 and SNU014201 from root nodules of Elaegnus umbellata and Alnus hirsuta. We have cloned nif-H, D, K, E, N, X, W, Z, B, U, S, A genes from EuIK1, and analyzed their sequences as well as expression patterns. Now, we focus on molecular mechanism of nif-gene expression.

B] Molecular studies on root nodule formation on plant's side have been poorly understood, especially in host plants of Frankia.. We have isolated several genes such as Asparagine synthetase, Glutamine synthetase, Chitinase, polyubiquitin, aminoaspartate transferase II, from Elaeagnus umbellata, that are expressed specifically or strongly in root nodule by using competitive differential screening. Now, we focus on their expression pattern by localization in root nodule.

2. Plant's Response to Environmental Stress

A) Plant's Response to Oxidative Stress

Reactive oxygen species (ROS) are toxic by-products of oxidative metabolism. They can react indiscriminately with DNA, proteins, lipids, and almost any constituent of cells. The electron-transport chains present within the different subcellular compartments are well documented sources of ROS. Both enzymic and nonenzymic mechanisms have evolved to overcome oxygen toxicity. These include antioxidants such as glutathione, ascorbate, and ¥á-tocopherol, and enzymes such as glutathione reductase which reduces glutathione, catalase and peroxidases which removes H₂O_2, and superoxide dismutase (SOD) which converts superoxide to hydrogen peroxide. We have focused on these enzymes in small radish and red pepper. We isolated Cu/Zn-, Mn-, and FeSOD cDNAs, three catalase, two peroxidase and one GR clones, and examined their expression patterns during development and under stress condition. We now focus on the regulation mechanism of their expression.

B) Expression Mechanism of Genes Involved Flavonoids Biosynthesis

A tremendous array of plant natural products is synthesized from phenylalanine via a series of biosynthetic pathways collectively termed phenylpropanoid metabolism. Phenylpropanoid metabolism required for the synthesis of all phenylpropanoid metabolite and specific branch pathways. Among the best studied of these pathways are those leading to the synthesis of flavonoids (key enzymes include PAL, CHS, CHI) and lignin (key enzyme include CAD). We isolated cDNA clones of CHI, CHS from small radish and studied their tissue specific expression through northern hybridization. We continue studies on the clonning of other genes such as DFR, and their expression patterns under variety of stress condition.