The cis-Acting Gibberellin Response Complex in High-pl [alpha]-Amylase Gene Promoters (Requirement of a Coupling Element for High-Level Transcription)

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Abstract
In cereal [alpha]-amylase gene promoters the cis-acting gibberellin response element (GARE) is required for increased transcription in the presence of gibberellin. In low-isoelectric point (pl) [alpha]-amylase gene promoters a second type of cis element, termed a coupling element, must also be present in a specific position near the GARE; otherwise, the level of transcription in the presence of gibberellin is only a few percent of maximum. The coupling element may help determine where and when in development high-level, hormonally regulated transcription will occur. Such coupling elements have not yet been shown to be necessary for high-level transcription from high-pl [alpha]-amylase gene promoters. Here we use quantitative transient expression assays to show that a high-pl promoter truncated to -300 is a weak promoter due to the absence of a functional coupling element in the vicinity of the GARE. Gibberellin-induced transcription increases substantially when coupling element function is provided, either by appending upstream regions normally attached to the promoter or by inserting a defined coupling element from a low-pl promoter. Thus, in a second type of gibberellin-regulated promoter coupling element function was found to be crucial for hormone regulation to result in high-level transcription.