In Arabidopsis, cadmium exposure triggers SPL7-dependent copper deficiency responses, including increased copper uptake through COPT transporters, and these responses are required for basal cadmium tolerance.
Authors
- Gayomba, S. R., Jung, H., Yan, J., Danku, J., Rutzke, M. A., Bernal, M., Krämer, U., Kochian, L. V., Salt, D. E., & Vatamaniuk, O. K., Metallomics, 2013
What was studied
The study titled “The CTR/COPT-dependent copper uptake and SPL7-dependent copper deficiency responses are required for basal cadmium tolerance in A. thaliana” investigates whether exposure to the toxic heavy metal cadmium (Cd) disturbs copper (Cu) homeostasis in the model plant Arabidopsis thaliana. Plants maintain Cu balance in two ways: by reallocating Cu among the major Cu enzymes through microRNAs, and by regulating Cu transporters of the CTR/COPT family. Both are controlled by the transcription factor SPL7. Because cadmium is non-essential and competes with essential elements for cellular binding sites, the authors asked whether Cd affects Cu uptake and whether Cu homeostasis contributes to Cd tolerance. They measured Cu accumulation and transporter gene expression, and compared the Cd sensitivity of wild-type plants, copt transporter mutants, plants overexpressing COPT6, and spl7 mutants.
Who was studied
The research used Arabidopsis thaliana seedlings: wild-type plants; single and triple copt1 copt2 copt6 mutants lacking plasma-membrane Cu uptake transporters; transgenic plants ectopically expressing COPT6; and the spl7-1 mutant, which lacks the master regulator of the Cu deficiency response. No food crops or human subjects were studied. Arabidopsis is a laboratory model used to work out the genetic mechanisms of metal uptake and tolerance in plants.
Most important findings
| Critical Points | Details |
|---|---|
| Cadmium raises copper uptake | Cadmium stimulated Cu accumulation in the roots of A. thaliana and increased mRNA expression of three plasma-membrane Cu uptake transporters: COPT1, COPT2 and COPT6. |
| Copper uptake supports cadmium resistance | Analysis of the Cd sensitivity of single and triple copt1 copt2 copt6 mutants, and of plants ectopically expressing COPT6, indicated that Cu uptake is an essential component of Cd resistance. |
| Cadmium mimics copper deficiency | Cd-induced expression of the COPT transporters occurs partly by mimicking the SPL7-dependent transcriptional Cu deficiency response. This response also involves the Cu reallocation system: miRNA398 and the superoxide dismutases FSD1, CSD1 and CSD2. |
| SPL7 is required for basal tolerance | spl7-1 seedlings accumulated up to 2-fold less Cu in their roots than wild-type plants, were hypersensitive to Cd, and were more sensitive to Cd than the triple copt mutant. |
| Overall conclusion | Exposure to excess Cd triggers SPL7-dependent Cu deficiency responses, including Cu uptake and reallocation, and these responses are required for basal Cd tolerance in A. thaliana. |
Key implications
This research shows that the toxicity of a non-essential metal like cadmium cannot be separated from the plant's handling of essential micronutrients: Cd exposure pushes the plant into a copper-deficiency-like state, and the plant's ability to take up and reallocate copper helps it tolerate Cd. For heavy metal testing, the study is a reminder that essential and toxic metals interact inside the plant, so the uptake of one can depend on the status of another. The work was done in a laboratory model plant, so its findings on specific transporters and regulators will need confirmation before they can be applied to edible crops.
Citation
Gayomba, S. R., Jung, H., Yan, J., Danku, J., Rutzke, M. A., Bernal, M., Krämer, U., Kochian, L. V., Salt, D. E., & Vatamaniuk, O. K. (2013). The CTR/COPT-dependent copper uptake and SPL7-dependent copper deficiency responses are required for basal cadmium tolerance in A. thaliana. Metallomics, 5(9), 1262–1275.
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