11:10-12:00, Rm 103

The Early Stage of Plant Development: Seed Dormancy and GerminationS4-1Waking up in time, seed dormancy explained at the molecular levelWim J.J. SoppeDepartment of Plant Breeding and Genetics, Max Planck Institute for Plant Breeding Research,Carl-von-Linné-Weg 10, 50829 Cologne, GermanyPlants are sessile organisms whose survival depends on the adjustment of their life cycleto environmental and seasonal changes. The life cycle is determined by the timing of twomajor developmental transitions, germination and flowering. The control of flowering timeis increasingly well understood at the molecular level, but the regulation of germination isstill largely unclear. Germination timing is controlled by seed dormancy, which is definedas the incapacity of a viable seed to germinate under favourable conditions. In the modelplant Arabidopsis, dormancy is induced during the maturation of seeds in the silique andreleased by imbibition of seeds at low temperatures (stratification) or dry storage (afterripening).Seed dormancy is determined by the balance between the plant hormonesabscisic acid and gibberellins. High levels of abscisic acid are required for the induction ofseed dormancy, while gibberellins are necessary for germination. Physiological andgenetic research on seed dormancy identified additional roles for ethylene, sugars,phytochrome, brassinosteroids and nitrate. However, our knowledge about the molecularregulation of seed dormancy and its control by environmental factors is limited. To revealthe molecular mechanisms that determine the induction and release of seed dormancy,my research group has analysed and cloned Arabidopsis mutants with reduced dormancylevels. The underlying genes could be divided in two groups. The first group consists ofgenes with a general role in plant development that are expressed in all plant tissues.Transcription elongation factors are overrepresented in this group and most of thesegenes are upregulated towards the end of seed maturation. Interestingly, this upregulationis correlated with a strong reduction in nuclear size during seed maturation, whichsuggests that transcription elongation factors are required to facilitate gene expression innuclei with reduced volume. An example of a gene belonging to this group is HUB1,which encodes a C3HC4 RING finger protein that is required for monoubiquitination ofhistone H2B. We observed altered expression levels for several dormancy genes in thehub1 mutant towards the end of seed maturation. The second group consists ofdormancy genes with a seed-specific expression. The gene DELAY OF GERMINATION1 (DOG1), which is expressed during seed maturation and encodes a protein withunknown function, belongs to this group. DOG1 is essential for seed dormancy becausethe dog1 mutant is completely non-dormant. DOG1 expression is upregulated by reducedtemperatures during seed maturation. Higher levels of DOG1 protein in ripe seeds requirean increasing after-ripening time to release seed dormancy. DOG1 is alternatively splicedand we have shown that DOG1 function requires binding between its different proteinisoforms. In this seminar, I will present our present understanding of the molecularmechanism of seed dormancy in Arabidopsis and focus on the roles of transcriptionelongation factors and DOG1.S4-3Role of ABA signaling components in seed germinationSun-ji Lee and Soo Young KimDepartment of Molecular Biotechnology & Kumho Life Science Laboratory, College of Agriculture& Life Sciences, Chonnam National University, Gwangju 500-757, KoreaAbscisic aicd (ABA) is a phytohormone that regulates various aspects of plantdevelopment. During vegetative growth, ABA controls adaptive responses to variousabiotic stresses. During seed development, ABA regulates the synthesis of storagecomponents. Another important function of ABA is to protect embryos in dry seeds and toprevent them from precocious germination. Our lab is interested in identifying regulatorycomponents of ABA response, and one of the approaches we are employing is activationtagging. We screened a library of Arabidopsis activation-tagged seed pools and isolated anumber of ABA response mutants. One of them was selected for further study, and wewill present the result in the meeting. Briefly, the mutant was ABA-insensitive, and T-DNAwas inserted into the gene encoding one of the Raf-family MAPKKKs in the mutant. Inrecapitulation experiments, we observed a similar phenotype in SALK knockout mutants.To investigate the function of the gene further, we also prepared and analyzedoverexpression (OX) lines. One of the strong phenotypes observed in the OX lines isdelayed seed germination: we observed several days of delay in radical emergence, and,in some transgenic lines with higher expression levels of the MAPKKK gene, germinationdid not occur.S4-4Control of seed germination by posttranslational histone modificationYoo-Sun NohSchool of Biological Sciences, Seoul National University, Seoul 151-747, KoreaSeed germination, which distinguishes post-embryonic development from embryonicdevelopment, is one of the important developmental phase transitions in seed plants. Foroptimal survival, various environmental and endogenous factors should be monitoredproperly to determine appropriate timing for seed germination. Among environmentalfactors, light is perceived by phytochromes and promotes seed germination. Lightdependentactivation of phytochromes modulates ABA and GA levels by regulating boththeir metabolic and signaling pathways. Several negative regulators of seed germinationthat act when phytochromes are inactive have been reported. However, neither positiveregulators of seed germination nor direct mechanisms for the regulation of the hormonallevels have been reported. Here we report that two functionally redundant histonemodifiers act as positive regulators of seed germination. We show that loss of thesefactors leads to reduced germination efficiency when red light pulse is treated. Our studyalso shows the control of some key germination genes and modification of theirchromatins by these novel factors as well as a regulatory pathway involving them.S4-2Collaborative regulation of seed germination by PIL5 and othertranscription factorsJeongmoo Park, Hyojin Kang, Woohyun Kim, Junhyun Kim and Giltsu ChoiDepartment of Biological Sciences, KAIST, Daejeon 305-701, KoreaPIL5, also known as PIF1, is a phytochrome-interacting basic helix-loop-helix transcriptionfactor that inhibits seed germination in Arabidopsis. It binds to G-box elements (CACGTG)present in various promoters and regulates the expression of genes associated with thosepromoters. A genome wide analysis of its binding sites coupled with a gene expressionanalysis indicated that PIL5 binds to 748 sites and regulates the expression of 166 geneseither positively (105 genes) or negatively (61 genes) in imbibed seeds. The 166 genesinclude various hormone signaling genes and various cell wall modifying enzyme genes.These analyses suggested that the phytochrome-PIL5 signaling module regulates seedgermination by coordinating hormone signaling and cell wall properties in imbibed seeds.We further investigated why PIL5 binds to only a subset of G-box elements out of 29,251G-boxes in the genome. Our analysis indicates that many PIL5-bound G-boxes arecoupled with other elements. These coupling elements can also partially explain non G-box PIL5-binding sites. Taken together, our data suggest that that PIL5 binds to its targetin the presence of coupling transcription factors.S5-1Targeting of α-chain of the nascent-polypeptide-associated complex(NACA) induces mitotic arrest of tumor cell cycleMIN-JEONG KIM, MI-JIN LEE, MI-NA SEOL, GYUNG-RAN YU, HEE-JUNG YOO, IN-HEE KIM, DAE-GHON KIMDivision of Gastroenterology and Hepatology, Departments of Internal Medicine, ChonbukNational University Medical School and Hospital, Jeonju, Jeonbuk, KoreaNACA (the αchain of the nascent-polypeptide-associated complex), a transcriptional coactivator,was preferentially expressed in hepatocellular carcinomas (HCCs) andhepatoma cell lines. However, the biological implication of overexpression and theusefulness of therapeutic target in HCC remain elucidative. NACA was overexpressed inHCCs, which is positively correlated with Edmondson differentiation grades and TNMstages (P = .001 and P = .048, respectively). The knockdown of NACA resulted indecrease of tumor cell proliferation and soft agar colony generation in experimental cellculture. NACA shRNA inhibited the expression and phosphorylation of extracellularsignal-regulated kinase 1 and 2 (ERK1 and 2), a member of the MAP kinase family.Interestingly, NACA overexpression was observed during the mitotic stage of cell cyclephase and its knock-down resulted in G2/M arrest in HCC cells, which was correlated withdownregulation of G2/M cyclins and related molecules. The knock-down of NACA alsoinhibited HCC growth in xenoplanted mice. Conclusion: NACA gene silencing usinglentiviral delivery of shRNA inhibited tumor cell growth in vitro and in vivo throughinhibition ERK signaling and mitotic arrest of tumor cell cycle. Therefore, this strategy maybe useful as a novel therapeutic modality for HCC.72 Korean Society for Biochemistry and Molecular Biology