Abstract:

The conversion of putrescine to spermidine in the biosynthetic pathway of plant polyamines is catalyzed by two closely related spermidine synthases, SPDS1 and SPDS2, in Arabidopsis. In the yeast two-hybrid system, SPDS2 was found to interact with SPDS1 and a novel protein, SPMS (spermine synthase), which is homologous with SPDS2 and SPDS1. SPMS interacts with both SPDS1 and SPDS2 in yeast and in vitro. Unlike SPDS1 and SPDS2, SPMS failed to suppress the speDelta3 deficiency of spermidine synthase in yeast. However, SPMS was able to complement the speDelta4 spermine deficiency in yeast, indicating that SPMS is a novel spermine synthase. The SPDS and SPMS proteins showed no homodimerization but formed heterodimers in vitro. Pairwise coexpression of hemagglutinin- and c-Myc epitope-labeled proteins in Arabidopsis cells confirmed the existence of coimmunoprecipitating SPDS1-SPDS2 and SDPS2-SPMS heterodimers in vivo. The epitope-labeled SPDS and SPMS proteins copurified with protein complexes ranging in size from 650 to 750 kD. Our data demonstrate the existence of a metabolon involving at least the last two steps of polyamine biosynthesis in Arabidopsis.

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A Polyamine Metabolon Involving Aminopropyl Transferase Complexes in Arabidopsis

^{Unitat de Fisiologia Vegetal, Facultat de Farmàcia, Universitat de Barcelona, Diagonal 643, 08028-Barcelona, Spain}

^{Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia–Consejo Superior de Investigaciones Científicas, Avda de los Naranjos s/n, 46022 Valencia, Spain}

^{Max-Planck-Institut für Züchtungsforschung, Carl-von-Linné-Weg 10, D-50829 Köln, Germany}

^{To whom correspondence should be addressed. E-mail}se.bu.raf.aicamraf@nanrefa; fax 34-93-4029043

Received 2002 Apr 22; Accepted 2002 Jun 17.

Abstract

The conversion of putrescine to spermidine in the biosynthetic pathway of plant polyamines is catalyzed by two closely related spermidine synthases, SPDS1 and SPDS2, in Arabidopsis. In the yeast two-hybrid system, SPDS2 was found to interact with SPDS1 and a novel protein, SPMS (spermine synthase), which is homologous with SPDS2 and SPDS1. SPMS interacts with both SPDS1 and SPDS2 in yeast and in vitro. Unlike SPDS1 and SPDS2, SPMS failed to suppress the speΔ3 deficiency of spermidine synthase in yeast. However, SPMS was able to complement the speΔ4 spermine deficiency in yeast, indicating that SPMS is a novel spermine synthase. The SPDS and SPMS proteins showed no homodimerization but formed heterodimers in vitro. Pairwise coexpression of hemagglutinin- and c-Myc epitope–labeled proteins in Arabidopsis cells confirmed the existence of coimmunoprecipitating SPDS1-SPDS2 and SDPS2-SPMS heterodimers in vivo. The epitope-labeled SPDS and SPMS proteins copurified with protein complexes ranging in size from 650 to 750 kD. Our data demonstrate the existence of a metabolon involving at least the last two steps of polyamine biosynthesis in Arabidopsis.

Abstract

Acknowledgments

The authors thank H. Tabor and N. Hamasaki-Katagiri for providing the yeast speΔ3 and speΔ4 mutants and A. Pegg for supplying data before publication, as well as members of the Arabidopsis Genetics Group at the Max-Planck-Institut für Züchtungsforschung and N. Jovanovic (Universitat de Barcelona) for their help in this study. This work was supported by grants from the Ministerio de Ciencia y Tecnología (BIO-99-453 to A.F.T. and Bio99-1201-CO2-1 to J.C.) and the Deutsch Forschungsgemeinschaft (KO 1438/3-2 to C.K.).

Acknowledgments

Notes

Article, publication date, and citation information can be found at www.plantcell.org/cgi/doi/10.1105/tpc.004077.

Notes

Article, publication date, and citation information can be found at www.plantcell.org/cgi/doi/10.1105/tpc.004077.

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