Chair Professor National Chung Hsing university Taichung, Taichung, Taiwan (Republic of China)
Body of Abstract: How cell division is suppressed in differentiated cells but not meristematic cells and further causes the endoreduplication is largely unknown in plants. Here, we demonstrate that the Arabidopsis Yippee-like (YPEL) gene SUPPRESSOR FOR CELL DIVISION (SCD) was constitutively expressed in all tissues except meristematic cells. Importantly, the SCD proteins were constantly degraded in non-dividing cells and were activated to suppress cell division once these well-differentiated cells underwent abnormal cell division. Accelerated growth and increased leaf size were observed in 35S::SCD RNAi plants. In contrast, growth was significantly inhibited due to the production of compromised meristem structures and a lack of the cell division in shoot and root apical meristems in 35S::SCD plants. Furthermore, suppression of cell growth in the tobacco cell line BY-2 and the human embryonic kidney cell line HEK 293T was observed after transfection with SCD. In addition, transgenic Arabidopsis ectopically expressing SCD orthologue PaSCD from Phalaenopsis orchid showed similar altered phenotype as seen in 35S::SCD Arabidopsis. Flow-cytometric analysis demonstrated that proportion of 2C and 4C peaks clearly reduced whereas 32C and 64C peaks increased in 35S::SCD and 35S::PaSCD Arabidopsis. In contrast, 2C and 4C peaks increased whereas 32C and 64C peaks reduced in 35S::SCD RNAi Arabidopsis. Further analysis indicated that cyclin CYCB1,1 level is reduced in 35S::SCD, 35S::PaSCD and increased in 35S::SCD RNAi plants. These results indicate the efficiency for cell cycle entry to endocycle increased in 35S::SCD, 35S::PaSCD and reduced in 35S::SCD RNAi Arabidopsis. Our data show that SCD acts dual roles in inhibiting cell division and promoting the endoreduplication in plants.