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Title: CYTOKININ AND METALS REGULATE A TOBACCO METALLOTHIONEIN-LIKE GENE

Author
item THOMAS, JOHN - UNIV OF MICHIGAN
item PERRON, MIKE - UNIV OF MICHIGAN
item LAROSA, P - UNIV OF NEBRASKA
item Smigocki, Anna

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2004
Publication Date: 1/1/2005
Citation: Thomas, J.C., Perron, M., Larosa, P.C., Smigocki, A.C. 2005. Cytokinin and metals regulate a tobacco metallothionein-like gene. Physiologia Plantarum. 123-262:271.

Interpretive Summary: Disease and pest problems and environmental stresses reduce the amount of food we produce from crops. This increases production costs for the farmer, raising food prices. Primary control of diseases and pests relies on chemicals that are not always effective, that need to be reapplied during the growing season, and that can damage our environment. Safer approaches need to be developed to effectively combat environmental stresses. We discovered that plants become resistant to a number of insects when they produce more of a particular plant hormone (cytokinin). We are investigating how cytokinin imparts resistance by studying what other traits (genes) are controlled by cytokinin. One of the genes we found to be regulated by cytokinin has been linked to environmental stresses (viral attack, wounding, toxic heavy metals). Tobacco plants overproducing cytokinin maintained similar levels of the gene product under stressed (toxic heavy metals) and unstressed conditions, whereas plants that did not make extra cytokinin had reduced levels of this gene product. Elevated levels of cytokinin were advantageous for survival of the stressed plants because the function of the gene implicated in the detoxification of heavy metals was preserved. This information will be used by scientists to increase our knowledge of plant stress response mechanisms and lead to the development of novel approaches for reducing the usage of harmful chemicals.

Technical Abstract: To isolate cytokinin responsive genes, Nicotiana plumbaginifolia shoots/rosettes containing the heat shock inducible isopentenyl transferase (ipt) gene (HS-ipt) were heat shocked and used to prepare a cDNA library that was screened with a HS-induced subtractive probe. The cDNA clone pCkn16A1 (Accession U35225) was recovered and found to contain an open reading frame predicted to be a metallothionein-like gene (MTL2). DNA analysis suggested that the MT-L2 gene was a member of a small gene family. In mature leaves of non-transformed N. plumbaginifolia and N. tabacum, copper stress stimulated a significant loss of MT-L2 mRNA transcripts. Under non-copper stressed conditions, HS-ipt induced (N. plumbaginifolia) or light induced (SSU-ipt) (N. tabacum) plants contained greater MT-L2 transcript concentrations than non-transformed or GUS transformed controls. Subsequent copper stress did not alter MT-L2 mRNA levels in the ipt containing and cytokinin accumulating transgenic plants. Cytokinin mediated increases in MT-L2 transcripts existing prior to or during copper stress could contribute to an observed 8-fold accumulation of copper in mature leaves compared to non-transformed plants. We conclude that tobacco MT-L2 mRNA copper responsiveness may be modulated by endogenous cytokinin supply.