Poster: Vegetative Development

Abs # 439: Spermidine synthase genes are essential for survival of Arabidopsis thaliana

Presenter:	Takahashi, Taku , perfect@sci.hokudai.ac.jp
Authors	Takahashi, Taku  (A)   Imai, Akihiro  (A)   Matsuyama, Takashi  (B)   Hanzawa, Yoshie  (A)   Tamaoki, Masanori  (B)   Saji, Hikaru  (B)   Shirano, Yumiko  (C)   Kato, Tomohiko  (D)   Hayashi, Hiroaki  (E)   Shibata, Daisuke  (C) (D)  Tabata, Satoshi  (D)   Komeda, Yoshibumi  (A) (E)
Affiliations:	(A): Division of Biological Sciences, Hokkaido University (B): National Institute for Environmental Studies (C): Mitsui Plant Biotechnology Research Institute (D): Kazusa DNA Research Institute (E): The University of Tokyo

The cellular polyamines putrescine, spermidine and spermine are ubiquitous nitrogen compounds that are generally recognized as being necessary for orderly patterns of growth and development in most organisms. In plants, they have been implicated in a variety of cellular processes, including control of cell division, response to stress, root formation, flowering, and retardation of senescence. We have previously revealed that disruption of the ACAULIS5 gene, which encodes spermine synthase in Arabidopsis thaliana, results in a severely dwarfed phenotype (Hanzawa et al., 2000). However, no direct genetic evidence indicating the significance of spermidine in plant cells has been obtained. The Arabidopsis genome has two genes encoding spermidine synthase, SPDS1 and SPDS2. In this study, we isolated T-DNA insertion mutants of both of these genes. While each mutant allele showed normal growth, the reciprocal cross gave birth to no double-mutant plants in an F2 population. We found that the double-mutant seeds were abnormally shrunken and had an embryo arrested at the heart stage. They contained no detectable level of spermidine and increased level of its precursor, putrescine. A nearly identical seed phenotype was also observed among the F2 seed population from the cross between the spds2-1 allele and SPDS1 RNAi transgenic lines. These results indicate that mutants defective in the function of spermidine synthase are embryonically lethal and are consistent with the fact that polyamines are absolutely required for eukaryotic cell growth.