Poster: Vegetative Development

Abs # 420: Involvement of SRD2-mediated snRNA transcription in dedifferentiation and meristem neo-formation

Presenter:	Ohtani, Misato , ss27182@mail.ecc.u-tokyo.ac.jp
Authors	Ohtani, Misato  (A)   Munetaka, Sugiyama  (A)
Affiliations:	(A): Botanical Gardens, Graduate School of Science, The University of Tokyo

Organogenesis in vitro, indicative of totipotency of plant cells, starts with dedifferentiation of differentiated somatic cells to acquire competence with respect to cell proliferation and organ redifferentiation. Then cells proliferate to form calli or primordia and in the resultant mass of cells, neo-formation of apical meristems take place. srd2 is a temperature-sensitive mutant of Arabidopsis thaliana that is defective in both two key events of organogenesis in vitro, i.e., dedifferentiation and meristem neo-formation, but is almost normal in cell proliferation per se. Hence this mutant has been expected to provide important clues for understanding mechanisms of organogensis in vitro and totipotency expression. Positional cloning of the responsible gene of this mutant, SRD2, indicated that it is correspondent to At1g28560. The predicted product shares sequence similarity with human SNAP50, a subunit of SNAPc (snRNA activating protein complex), which was identified as an activator of in-vitro snRNA transcription. RNA gel blot analysis revealed that the level of snRNA increased in hypocotyl explants induced to form callus, and that this increase was inhibited by the srd2 mutation. The SRD2 mRNA was accumulated transiently during dedifferentiation of hypocotys in response to auxin and cytokinin. These findings suggest that SRD2 functions in the up-regulation of snRNA transcription, which is involved in dedifferentiation as a prerequisite for initially incompetent cells to re-enter the cell cycle. Our recent analysis showed that the SRD2 mRNA increased again in calli or primordia just before establishment of apical meristems. Based on the results, we will discuss the entire process of organogenesis in vitro from the viewpoint of the SRD2-mediated snRNA transcription.