Stanislav's lab

 

 

NEW PUBLICATION
Watch out for newest review of sulfur metabolism
Takahashi H., Kopriva S., Giordano M., Saito K., Hell R. (2011) Sulfur Assimilation in Photosynthetic Organisms: Molecular Functions and Regulations of Transporters and Assimilatory Enzymes. Annu. Rev. Plant Biol., 62, 157-184.

 

Our research in plant nutrition is oriented on understanding the molecular basis of nutrient use efficiency and control of nutrient uptake and assimilation. A great part of our research concentrates on assimilation of sulfate, especially the key enzyme of the pathway the adenosine 5'-phosphosulfate reductase (APR). Using a combination of biochemical, physiological, and molecular methods we have shown that:
1. Sulphate assimilation is coordinated with the assimilation of nitrate and carbon. We demonstrated that nitrogen deficiency specifically affects the activity and mRNA level of APR and that feeding various nitrogen-containing compounds to nitrogen-starved plants rapidly increases flux through the sulphate assimilation pathway (Koprivova et al. 2000). We showed that APS reductase is regulated by light and sugars and that its transcript levels and enzyme activity undergo a diurnal rhythm (Kopriva et al. 1999). We demonstrated that in plants treated with sucrose or glucose APR was induced whereas the activity was strongly reduced in plants grown in CO2 free air (Kopriva et al. 1999; Kopriva et al. 2002; Hesse et al. 2003). We also revealed that APS reductase is regulated by salt stress at a post-transcriptional level in a complex, abscisic acid-independent manner (Koprivova et al 2008).
2. APS reductase is the enzyme controlling the flux through sulphate assimilation (Vauclare et al. 2002). In collaboration with O. Loudet and F. Daniel-Vedele (INRA Versailles) we have exploited Arabidopsis natural variation in combination with QTL analysis to show that sulphate content variation between Arabidopsis wild type accessions 'Bay-0' and 'Shahdara' is controlled by APS reductase (Loudet et al. 2007).
3. In a multidisciplinary approach with several laboratories we have characterised the biochemical mechanism of APS reductase. This work revealed that the APS reductase contains an iron-sulphur centre as a co-factor, forms a reaction intermediate with sulphite covalently bound to the protein, and that free sulphite is the product of the reaction (Suter et al. 2000; Kopriva et al. 2001; Weber et al. 2000). Our broader investigation of the function of APS reductase, using functional genomics in the moss Physcomitrella patens, led to the key discovery of a new alternative enzyme in mosses (Koprivova et al. 2002). This enzyme has been recently characterised as a novel form of APS reductase, APR-B, independent from the FeS chemistry (Kopriva et al. 2007; Wiedemann et al. 2007). We identified APR-B-like isoforms of APS reductase in genomes of several microalgae and showed by detailed phylogenetic analysis that this isoform evolved from a bacterial or fungal 3'-phosphoadenosine 5'-phosphosulphate reductase and not from the FeS containing APS reductase (Patron et al. 2008).
4. APS kinase is important for accumulation of glucosinolates and for partitioning of sulfur between primary and secondary metabolism. We carried out a systematic analysis of APS kinase gene family in Arabidopsis. Disruption of two of the 4 APS kinase genes, APK1 and APK2, resulted in a 90% reduction in the levels of the major group of sulfated metabolites, the glucosinolates. The reduction in glucosinolates was accompanied by increased levels of glutathione, indicating that a reduction in APS kinase activity channels sulfur towards primary metabolism (Mugford et al. 2009, 2011).

We have initiated new projects on genetic dissection of regulation of plant sulfate assimilation and nutrient use efficiency. In addition, within the Earth and Life Systems Alliance we analyse sulfur metabolism in marine microalgae.

Dr Stanislav Kopriva's curriculum vitae