Atsuhiko Shinmyo

cis‐Regulatory Elements of the Peroxidase Gene in Arabidopsis thaliana Involved in Root‐Specific Expression and Responsiveness to High‐Salt Stress

The pattern of organ-specific expression of Arabidopsis thaliana peroxidase was similar to that in horseradish. Tobacco plants transformed with the gus gene fused to the -580 bp deletion (Ea-580) of A. thaliana exhibited high GUS expression in roots. Gel retardation and footprinting analyses showed that at least three domains of fragment between -172 and -1 bp have cis-acting element activities. Several physiological functions for plant peroxidases have been suggested; for example, a metabolic adaptation to salinity in the environment can be induced by certain specific elements of the peroxidase gene. The prxEa promoter fragments (Ea-580 and Ea-390) show multiple cis-acting elements in the control of expression in high-salt stress. These data suggest that the DNA-binding factor may be involved in the regulation of gene expression in specific organ and salt stress.

Control of the G1/S Phase Transition in Tobacco BY-2 Cells

The ability of cells to clonally replicate is central to life, and the co-ordinated regulation of cell division with cell growth and differentiation is required for the development of multicellular organisms. The cell division cycle consists of DNA replication and the allocation of identical genetic information to two daughter cells through mitosis and cell division. As in other eukaryotic cells, the plant cell cycle consists of four different phases representing DNA synthesis (S phase) and mitosis (M phase) separated by two gaps, the G1 and G2 phases, such that cells pass in order through M, G1, S, and G2 phases. Although progression through the cell cycle is regulated at both the G1/S and G2/M phase transitions, the major checkpoint of cell division commitment occurs at the G1 phase. Once cells have passed through this checkpoint, they become irreversibly committed to complete the cell cycle (Murray et al. 2001; Oakenful et al. 2002).