臨時生物科学セミナー（第１６２回）

　　日　時：平成２０年４月１０日（木）　�@１６：００〜１７：１０

　　　　　　　　　 �A１７：２０〜１８：３０

場　所：理学部２号館　第二講義室（２２３号室）

�@１６：００〜１７：１０

講演題目：Cytokinin action in the vasculature development of Arabidopsis

講演者名：Prof. Ildoo Hwang

講演概要

Cytokinins play essential roles in cell division and vascular tissue development. While cytokinin signals are perceived by the histidine kinase receptors AHK2, AHK3, and AHK4/CRE1/WOL, recent genetic analyses indicate the existence of additional cytokinin signaling pathway in Arabidopsis. Here we show that histidine kinase CKI1 constitutively activates the cytokinin signaling pathway. CKI1 induces expression of cytokinin-responsive type-A ARRs and ARR2 phosphorylation in cytokinin-deficient and wild-type protoplasts and dominant negative CKI1 allele suppresses AHKs-dependent activation of ARR6. CKI1 expression was found in vascular tissues, root tip and shoot apex. Ectopic expression of CKI1 causes abnormal cell division and differentiation in the vascular bundles of inflorescence stems and in axillary meristems. Reduction of CKI1 expression in plants by RNA interference or T-DNA insertion reveals aberrations in the inflorescence vascular tissue development. These results suggest that the constitutive CKI1 activity connects to two-component circuitry mediated by cytokinin signaling and regulates vascular tissue development in Arabidopsis.

�A１７：２０〜１８：３０

講演題目：Regulation of cell division and cell differentiation in shoot apical meristem and leaves

講演者名：Dr. Gyung-Tae Kim

Department of Molecular Biotechnology, Dong-A University, Busan 604-714, Korea

講演概要

Leaf shape is controlled early on by initiation at the shoot apical meristem (SAM), as well as by changes in the rates and planes of cell division and the polarity-dependent differentiation of leaf cells. Recent study of Kip-related proteins (KRPs), which are inhibitor of cyclin-dependent kinase (CDK), indicated that negative regulation of cell division plays an important role in plant morphogenesis. To investigate how KRPs control SAM structure and leaf morphology, we have characterized transgenic Arabidopsis overexpressing KRP families. Transgenic plants overexpressing KRPs commonly had reduced size of leaves with serration and resulted in small size of plant. Interestingly, rolling up and curvature phenotype of leaves was observed only in transgenic plants overexpressing KRP6. These results suggested that KRP family might have different roles in tissue level and developmental stages.

On the other hand, our genetic study of deformed root and leaf1 (drl1) mutant, which produces narrow, filament-like leaves and defective meristems, revealed that DRL1 is involved in the regulation of SAM activity and leaf polarity. The DRL1, which encodes Elongator-associate protein, is universally conserved in prokaryotes and eukaryotes. Our study suggests that DRL1 might positively regulate leaf polarity and SAM activity via controlling cell proliferation and differentiation. Taken together, I will discuss about the regulation of cell division and cell differentiation in SAM and leaves.

　東京大学理学部生物学科植物学コース