2006년 4월 6일 오후 4시 30분
The Roles of RNA-Binding Proteins in Plant Stress Responses
Hunseung Kang (강훈승)
Department of Plant Biotechnology, Chonnam National University
(전남대학교 농업생명과학대학 식물생명공학부)
Although a number of studies have demonstrated that RNA-binding proteins (RBPs) are involved in plant responses to environmental stresses, the functional roles of RBPs under stress conditions are largely unknown. To understand the function of RBPs and the mechanism by which RBP-mediated posttranscriptional regulation of gene expression in plants under various environmental stresses, the gene families encoding glycine rich-RBP (GR-RBP), zinc finger-RBP, and cold shock domain-RBP (CSD-RBP) were characterized for their nucleic acid-binding property, expression pattern and function in stress responses in Arabidopsis thaliana. Nucleic acid-binding capabilities of the RBPs vary depending on the types of RBPs. All the RBPs investigated were highly up regulated by cold stress, and were differently regulated by drought or high salinity stress. Analyses of the T-DNA tagged knockout mutants and overexpression transgenic plants revealed that RBPs play fundamental roles in cold, salt, or drought stress adaptation process in plant. Freezing test and heterologous expression of RBPs in Escherichia coli revealed that RBPs contribute to freezing tolerance in Arabidopsis and help E. coli grow and survive better during cold shock. Two-dimensional gel and proteome analyses suggest several target genes modulated by each RBPs. These results reveal that GR-RBPs, CSD-RBPs, and zinc finger-RBPs have multiple functions in plant response to various stresses, and particularly play roles as RNA chaperones during cold or freezing adaptation process. The current findings, limitations, and future prospects of RNA-binding proteins in plant responses to diverse environmental stimuli will also be discussed.
Lignan Biosynthesis in Larrea tridentata: Enantiospecific Aromatic Hydroxylation of Larreatricin
Creosote bush (Larrea tridentata) was widely used in traditional medicine among indigenous people of America for digestive disorders, rheumatism, venereal diseases and sores. Nordihydroguaiaretic acid (NDGA), the major constituent of its resinous exudate (5-10 % of leaf dry weight), is a powerful antioxidant and has been employed in non-food applications such as stabilizing polymer, rubber, perfumery oil and photographic formulations. Beside NDGA, creosote bush accumulates a vast array of 8-8¢ linked allyphenol-derived lignans. Of which, 3¢-O-methyl-NDGA and methylated/ acetylated NDGA derivatives has antiviral activities against HIV, herpes simplex virus and/or human papilloma virus.
Larreatricin, presumed coupling product of an allyphynol, anol, is considered to be an important intermediate involving regiospecific hydroxylation at C-3¢ in the biosynthesis of lignans in L. tridentata. A polyphenol oxidase catalyzing 3¢-hydroxylation of larreatricin to 3¢-hydroxylarreatricin was purified from the leaves of creosote bush by DEAE-Sepharose, Hydroxylapatite, and Phenyl Sepharose column chromatographies. The enzyme has a molecular weight of ~43 kD, and a broad pH optimum of pH 6 - 8. The enzymatic reaction is enantiospecific, with larreatricin 3¢-hydroxylase selectively introducing a hydroxyl group into (+)-larreatricin but not the corresponding enantiomeric form, (-)-larreatricin.