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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Impact of Reduced O-Acetylserine(thiol)lyase Isoform Contents on Potato Plant Metabolism¹

Institut für Botanik, Universität Hannover, D–30419 Hannover, Germany (A.R., J.P.); and Max-Planck-Institut für Molekulare Pflanzenphysiologie, Department of Molecular Physiology, D–14476 Golm, Germany (K.R., R.H., H.H.)

Plant cysteine (Cys) synthesis can occur in three cellular compartments: the chloroplast, cytoplasm, and mitochondrion. Cys formation is catalyzed by the enzyme O-acetylserine(thiol)lyase (OASTL) using O-acetylserine (OAS) and sulfide as substrates. To unravel the function of different isoforms of OASTL in cellular metabolism, a transgenic approach was used to down-regulate specifically the plastidial and cytosolic isoforms in potato (Solanum tuberosum). This approach resulted in decreased RNA, protein, and enzymatic activity levels. Intriguingly, H₂S-releasing capacity was also reduced in these lines. Unexpectedly, the thiol levels in the transgenic lines were, regardless of the selected OASTL isoform, significantly elevated. Furthermore, levels of metabolites such as serine, OAS, methionine, threonine, isoleucine, and lysine also increased in the investigated transgenic lines. This indicates that higher Cys levels might influence methionine synthesis and subsequently pathway-related amino acids. The increase of serine and OAS points to suboptimal Cys synthesis in transgenic plants. Taking these findings together, it can be assumed that excess OASTL activity regulates not only Cys de novo synthesis but also its homeostasis. A model for the regulation of Cys levels in plants is proposed.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.057125.

^* Corresponding author; e-mail hesse{at}mpimp-golm.mpg.de; fax 49–331–567898247.

Received November 23, 2004; returned for revision January 3, 2005; accepted January 3, 2005.

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