MOLECULAR ANALYSIS OF PLANT ORGAN AND TISSUE DEVELOPMENT

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This research is divided into two projects.1. Organ separation and shoot meristem formation I have isolated the cuc mutant in Arabidopsis thaliana, which seedlings have fused cotyledons and no shoot apical meristem. This mutant was caused by double mutations in CUCI and CUC2 genes and CUC2 genes was cloned. In this research, we made clear next 4 points. (1) The CUC genes were essential for initiation of STM expression to form shoot apical meristem. (2) STM was required for proper spatial expression of CUC2 at later stages to separate cotyledons. (3) CUC2 was expressed at boundaries between shoot apical meristem and leaf primordia, between inflorescence meristem and floral meristem, and among each organs of flowers. (4) CUCs were essential to form intact gynoecium and ovules in flowers.2. Shoot gravitropism ; Shoot shows negative gravitropism. To investigate molecular mechanisms of shoot gravitropism, we have isolated many reduced-gravitropic mutants from Arabidopsis thaliana and identified 9 new loci relating to shoot gravitropism, SGRl-7, RHG and SLR.In this research, we made clear next 4 points. (1) The SGRl, which encodes bZIP type transcription factor, and SGR7 were essential for endoderm cell differentiation in hypocotyl and inflorescence stem and endoderm cells were gravity perception cells in these organs. (2) The SLR gene encodes JAA 14 gene, which was a nuclear protein and important in auxin signaling pathway. (3) SGR2 was important for both shoot gravitropism and embryogenesis. (4) sgr4 was abnormal in amyloplastlocalization and movement in endoderm cells of hypocotyl and inflorescence stems causing reduced gravitropism.