Manipulation of thiol contents in plants

Citation
R. Hofgen et al., Manipulation of thiol contents in plants, AMINO ACIDS, 20(3), 2001, pp. 291-299
Citations number
34
Categorie Soggetti
Biochemistry & Biophysics
Journal title
AMINO ACIDS
ISSN journal
09394451 → ACNP
Volume
20
Issue
3
Year of publication
2001
Pages
291 - 299
Database
ISI
SICI code
0939-4451(2001)20:3<291:MOTCIP>2.0.ZU;2-D
Abstract
As sulfur constitutes one of the macronutrients necessary for the plant lif e cycle, sulfur uptake and assimilation in higher plants is one of the cruc ial factors determining plant growth and vigour, crop yield and even resist ance to pests and stresses. Inorganic sulfate is mostly taken up as sulfate from the soil through the root system or to a lesser extent as volatile su lfur compounds from the air. In a cascade of enzymatic steps inorganic sulf ur is converted to the nutritionally important sulfur-containing amino acid s cysteine and methionine (Hell, 1997; Hell and Rennenberg, 1998; Saito, 19 99). Sulfate uptake and allocation between plant organs or within the cell is mediated by specific transporters localised in plant membranes. Several functionally different sulfate transporters have to be postulated and have been already cloned from a number of plant species (Clarkson et al., 1993; Hawkesford and Smith, 1997; Takahashi et al., 1997; Yamaguchi, 1997). Follo wing import into the plant and transport to the final site of reduction, th e plastid, the chemically relatively inert sulfate molecule is activated th rough binding to ATP forming adenosine-5 ' -phosphosulfate (APS). This enzy matic step is controlled through the enzyme ATP-sulfurylase (ATP-S). APS ca n be further phosphorylated to form 3 ' -phosphoadenosine-5 ' -phosphosulfa te (PAPS) which serves as sulfate donor for the formation of sulfate esters such as the biosynthesis of sulfolipids (Schmidt and Jager, 1992). However , most of the APS is reduced to sulfide through the enzymes APS-reductase ( APR) and sulfite reductase (SIR). The carbon backbone of cysteine is provid ed through serine, thus directly coupling photosynthetic processes and nitr ogen metabolism to sulfur assimilation. L-serine is activated by serine ace tyltransferase (SAT) through the transfer to an acetyl-group from acetyl co enzyme A to form O-acetyl-L-serine (OAS) which is then sulhydrylated using sulfide through the enzyme O-acetyl-L-serine thiol lyase (OAS-TL) forming c ysteine. Cysteine is the central precursor of all organic molecules contain ing reduced sulfur ranging from the amino acid methionine to peptides as gl utathione or phytochelatines, proteines, vitamines, cofactors as SAM and ho rmones. Cysteine and derived metabolites display essential roles within pla nt metabolism such as protein stabilisation through disulfide bridges, stre ss tolerance to active oxygen species and metals, cofactors for enzymatic r eactions as e.g. SAM as major methylgroup donor and plant development and s ignalling through the volatile hormone ethylene. Cysteine and other metabol ites carrying free sulfhydryl groups are commonly termed thioles (confer Pi g. 1). The physiological control of the sulfate reduction pathway in higher plants is still not completely understood in all details. The objective of this paper is to summarise the available data on the molecular analysis an d control of cysteine biosynthesis in plants, and to discuss potentials for manipulating the pathway using transgenic approaches.