Many transgenic plant studies use constitutive promoters to express transgenes. For certain genes, deleterious effects arise from constant expression in all tissues throughout development. We describe a chemically inducible plant gene expression system, with negligible background activity, that obviates this problem. We demonstrate its potential by showing inducible manipulation of carbon metabolism in transgenic plants. Upon rapid induction of yeast cytosolic invertase, a marked phenotype appears in developing leaves that is absent from leaves that developed before induction or after it has ceased.
SummaryWe describe a chemically induced gene control mechanism for plants based on the ALCR transcription factor and alcA promoter of Aspergillus nidulans, which we have called the alc system. Ethanol, the chemical inducer, is not toxic at levels required for induction, and can be applied to the plants by spraying, root drenching and addition to liquid growth media. The alc system is very sensitive to ethanol and the induction is rapid; 0.01% (1.7 mM) ethanol in liquid growth media initiates chloramphenicol acetyl transferase (CAT) reporter gene expression within 4 h, with maximal expression occurring after 4 days. In the complete absence of ethanol, there is no detectable expression of CAT, nor do we observe induction in plants subjected to wound, cold or drought stress, or following treatment with either salicylic acid or methyl jasmonate. However, extreme anoxia resulting in elevated levels of alcohol dehydrogenase activity in both roots and leaves gave substantial induction of CAT in leaves but not in roots. We believe that the alc system will have broad utility in the exogenous control of plant gene expression in pure science and that it also has considerable potential in agriculture.
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