Poster: Vegetative Development

Abs # 434: How the nucleus is degraded during developmentally programmed cell death?

Presenter:	Fukuda, Hiroo , fukuda@biol.s.u-tokyo.ac.jp
Authors	Fukuda, Hiroo  (A) (B)  Obara, Keisuke  (A)   Kuriyama, Hideo  (B)   Ito, Jun  (A)
Affiliations:	(A): Dept of Biol Sci, Grad Sch. of Sci, Univ. of Tokyo (B): Pl Sci Center, RIKEN

In most multicellular organisms, programmed cell death (PCD) is built into the process of their normal development and growth. One of key events in PCD is nuclear degradation. We found that in PCD during tracheary element (TE) differentiation, apart from apoptosis in animals, the vacuole plays a central role in the nuclear degradation. Serial observation of the nucleus in differentiating TEs revealed that nuclear DNA is degraded only after the vacuole ruptures. This fact suggests that a DNase responsible for nuclear DNA degradation accumulates in the vacuole during TE PCD. We found out a S1-type nuclease designated ZEN1, whose mRNA accumulates in TE PCD-specific manner. Enzymatic characterization of ZEN1 revealed that this enzyme could degrade nuclear DNA in vitro with other cytoplasmic factors, and the removal of this enzyme with a specific antibody did not cause DNA degradation, demonstrating that ZEN1 is a key nuclease for nuclear DNA degradation. Indeed the introduction of an antisense construct of ZEN1 into differentiating TEs suppressed nuclear degradation but not vacuole rupture. Analysis of subcellular localization of ZEN1 with an electron microscope and cultured tobacco cells harboring ZEN1 revealed that ZEN1 is targeted into the vacuole via the ER and the Golgi apparatus in differentiating TEs. We also found other nucleases that may be involved in nuclear degradation in TE PCD. Based on these findings, we will discuss how the nucleus is degraded during TE PCD.