Plant and Cell Physiology, 2002, Vol. 43, No. 3 275-280
© 2002 Oxford University Press
Activation of the Promoters of Arabidopsis Genes for the Branched-Chain
-Keto Acid Dehydrogenase Complex in Transgenic Tobacco BY-2 Cells under Sugar Starvation
Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
Sugar starvation exerted by sub-10 mM levels of sucrose on Arabidopsis T87 suspension-cultured cells triggered marked accumulation of the transcripts of genes for E1ß and E2 subunit of the branched-chain
-keto acid dehydrogenase complex. Similar levels of sugar starvation increased the luciferase activity in transgenic tobacco BY-2 lines expressing the Arabidopsis E1ß- or E2-promoter-luciferase fusion gene. These results indicate that sugar levels tightly regulate the E1ß and E2 promoter activity in the heterologous plant system. We further showed in the transgenic tobacco BY-2 lines that sugar-starvation-induced activation of the E1ß and E2 promoters was prevented by K-252a, an inhibitor of Ser/Thr protein kinase, and was enhanced by okadaic acid, an inhibitor of protein phosphatases. By contrast, the cauliflower mosaic virus 35S promoter activity in sugar-starved BY-2 cells was not significantly affected by K-252a and only slightly enhanced by okadaic acid. Taken together, we propose that transcriptional activation of genes for the branched-chain
-keto acid dehydrogenase complex and its modulation by specific protein kinases/phosphatases are of critical importance in branched-chain amino acid catabolism in plant cells under sugar starvation.
1 Present address: Pflanzenphysiologie, ZMBP, Universitaet Tuebingen, Auf der Morgenstelle 1, D-72076 Tuebingen, Germany.
2 Corresponding author: E-mail, yuki.fujiki@zmbp.uni-tuebingen.de; Fax, +81-3-3814-1728.
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