PLANT PHYSIOLOGY , Vol 102, Issue 3 1009-1018, Copyright © 1993 by American Society of Plant Biologists
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MOLECULAR BIOLOGY AND GENE REGULATION |
Regulation of Tobacco Acetolactate Synthase Gene Expression
S. J. Keeler, P. Sanders, J. K. Smith and B. J. Mazur
Agricultural Products Department, E. I. Du Pont de Nemours & Co., Experimental Station 402, Wilmington, Delaware 19880-0402
Acetolactate synthase (ALS) catalyzes the first common step in the
biosynthesis of isoleucine, leucine, and valine. The previous cloning of
two tobacco (Nicotiana tabacum) ALS genes (SurA and SurB) has allowed
transcript accumulation from these genes to be monitored. mRNA blot
analysis of ALS transcripts showed a message size of 2.2 kb. Quantitation
of the levels of ALS messages in tobacco organs indicated that there was a
3- to 4-fold variation in the levels of expression of the ALS genes in
different organs. This variability correlated with the developmental stage
of the samples, with the highest levels of expression found in developing
organs. In situ hybridizations of anti-mRNA probes to plant sections
established that ALS messages are most prevalent in metabolically active
and dividing cells of roots, stems, and floral tissue. Using RNase
protection assays, the transcriptional start sites of the ALS genes were
determined, and the expression levels of the two tobacco ALS genes were
then followed separately. Both tobacco ALS genes are expressed in a
coordinated manner in all tobacco organs examined, with the SurB gene being
consistently expressed at higher levels than the SurA gene.
