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Functional Analysis of Methylthioribose Kinase Genes in Plants

Margret Sauter, Kenneth A. Cornell, Sára Beszteri and Guillaume Rzewuski
Plant Physiology
Vol. 136, No. 4 (Dec., 2004), pp. 4061-4071
Stable URL: http://www.jstor.org/stable/4356759
Page Count: 11
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Functional Analysis of Methylthioribose Kinase Genes in Plants
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Abstract

Through a biochemical and a genetic approach, we have identified several plant genes encoding methylthioribose (MTR) kinase, an enzyme involved in recycling of methionine through the methylthioadenosine (MTA) cycle. OsMTK1, an MTR kinase from rice (Oryza sativa), is 48.6 kD in size and shows cooperative kinetics with a Vmax of 4.9 pmol/min and a K0.5 of 16.8 μM. MTR kinase genes are the first genes to be identified from the MTA cycle in plants. Insertional mutagenesis of the unique AtMTK gene in Arabidopsis (Arabidopsis thaliana) resulted in an inability of plants to grow on MTA as a supplemental sulfur source. MTK knock-out plants were not impaired in growth under standard conditions, indicating that the MTA cycle is a nonessential metabolic pathway in Arabidopsis when sulfur levels are replete. In rice, OsMTK genes were strongly up-regulated in shoots and roots when plants were exposed to sulfur starvation. Gene expression was largely unaffected by lack of nitrogen or iron in the nutrient solution, indicating that OsMTK regulation was linked specifically to sulfur metabolism.

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