Negative and positive regulators

In most plant systems analyzed so far sulfate, cysteine and GSH are described as negative regulators and OAS as positive regulator of sulfur genome (Hell 1997, Droux 2004). Analysis of the abundance of ATP-S1 and APS reductase mRNAs in Vitis vinifera cells as a response to sulfate deficiency, sulfate

AtSeraG;2

Fig. 7. Phylogenetic analysis of serine acetyl transferase amino acid sequences from Arabidopsis thaliana and hypothetical protein sequences of Vitis vinifera with homology to A. thaliana. Accession numbers from NCBI: Arabidopsis thaliana: AtSerat1;1, NP_200487.1; AtSerat2;1, NP_175988; AtSerat2;2, NP_187918; AtSerat3;1, NP_565421.1; AtSerat3;2, NP_195289.3; Vitis vinifera: Vv1-7, each sequence is indicated in the tree by the correspondent NCBI accession number. Alignments performed using the T-COFFEE web service (Notredame et al. 2000) and the resulting unrooted tree drawn using TreeView version 1.6.6 (Page 1996).

AtSeraG;2

re-supply, GSH, cysteine or OAS addition (Fig. 9) confirmed that SO42- and the thiol metabolites cysteine and GSH are strong negative regulators of APR expression (Vauclare et al. 2002). OAS has been considered as a general regulator of gene expression in response to sulfur nutrition (Hirai et al. 2003). Supply of exogenous OAS to various higher plant systems showed that it can have a limiting effect on cysteine synthesis (Neuenschwander et al. 1991) and it can also cause de-repression of sulfate reduction pathway (Hatzfeld et al. 1998). In Vitis cells growing in sulfur medium the effect of OAS was responsible for a 4-fold de-repressing of APSR expression and a 3-fold in ATP-S. The up-regulation of grapevine ATP-S is of the same order of magnitude as ATP-S activity in maize cells treated with OAS (Clarkson et al. 1999).

Fig. 8. Relative expression of the genes for of the sulfate assimilation enzymes in Vitis vinifera cv Touriga Nacional cells after 7 days under sulfate deprivation (-S) conditions. mRNA was analyzed as in Fig. 2 (Tavares et al. unpublished).

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