The Cytosolic O-Acetylserine(Thiol)Lyase Gene Is Regulated by Heavy Metals and Can Function

The Cytosolic O-Acetylserine(thiol)lyase Gene Is Regulated by Heavy Metals and Can Function in Cadmium Tolerance.

Jose R. Domýnguez-Solý’s, Gloria Gutierrez-Alcala , Luis C. Romero, and Cecilia Gotor

From the Instituto de Bioquýmica Vegetal y Fotosýntesis, Centro de Investigaciones Cientýficas Isla de la Cartuja, Consejo Superior de Investigaciones Cientificas and Universidad de Sevilla, Avda Americo Vespucio s/n, 41092 Sevilla, Spain

THE JOURNAL OF BIOLOGICAL CHEMISTRY Vol. 276, No. 12, Issue of March 23, pp. 9297–9302, 2001

Widespread contamination,

Bioremediation,

Hyper-accumulator,

Cadmium,

CdCl2 used,

Retreival.

Process of tolerance led by the synthesis of phytochelatins to chelate metal ions. Stored in vacuole once inactivated. Phytochelatins synthesised from glutathione in response to stress from heavy metals.

Microscope photograph of Glutathione

Courtesy of Florida State University

Cysteine biosynthesis – final step catalysed by:

O- acetylserine(thiol)lyase enzyme (OASTL)

OASTL is formed from L-serine catalysed by Serine acetyltransferase enzyme.

Both these enzymes are found in three locations: cytosol, chloroplast and mitochondria.

The experiment looks at induction of OASTL by Cd, and its involvement in Cd tolerance, by overexpression of the corresponding cDNA. The researchers isolated the Atcys-3A gene (cDNA) encoding the cytosolic isoform of OASTL from Arabidopsis thaliana. In situ hybridization studies showed the highest expression of Atcys-3A mRNA in trichomes of either leaf or stem.

Atcys–3A gene is regulated by salt stress and abcissic acid.

Plant Transformation

To measure the effect of cadmium on Atcys-3A transcript abundance. plants were fed 50m of CdCl2.

Atcys-3A shows a seven fold increase after 18 hours, with OASTL activity showing a 2.5 fold increase.

Circadian experiments using the CCA1 gene as a positive control showed there was no diurnal rhythm of Atcys-3A over 60 hours, suggesting that cadmium is the cause of the increased activity.

Table 1 has been redrawn and charted below

Next step

Cadmium tolerance in transformed plants overexpressing the Atcys-3A gene.

Resistance to cadmium by Atcys-3A plants means that cysteine is a main factor for tolerance as well as in forming glutathione?

Cystine (lacks free thiol group of cysteine) was added to avoid a reaction occurring in the medium. The pBI121 control plants were used in this experiment, being given 200μm cystine and 250μm of cadmium.

Mature transformed plants were then given cadmium at a concentration of 250μm for 14 daysand leaves were analysed by atomic emissiom spectrometry. The results are in the table below and graphed

Comparison of transformed plants and wild type at various concentrates. Graph above shows the cadmium content of leaves. Graph below shows the glutathione content of leaves.

References

University of Wales:

Florida State University: