AUX IAA PROTEINS REPRESS EXPRESSION OF REPORTER GENES CONTAINING NATURAL AND HIGHLY-ACTIVE SYNTHETIC AUXIN RESPONSE ELEMENTS/

A highly active synthetic auxin response element (AuxRE), referred to as DR5, was created by performing site-directed mutations in a natural composite AuxRE found in the soybean GH3 promoter. DR5 consisted of t andem direct repeats of 11 bp that included the auxin-responsive TGTCT C element. The DR5 AuxRE showed greater auxin responsiveness than a na tural composite AuxRE and the GH3 promoter when assayed by transient e xpression in carrot protoplasts or in stably transformed Arabidopsis s eedlings, and it provides a useful reporter gene for studying auxin-re sponsive transcription in wild-type plants and mutants. An auxin respo nse transcription factor, ARF1, bound with specificity to the DR5 AuxR E in vitro and interacted with Aux/IAA proteins in a yeast two-hybrid system. Cotransfection experiments with natural and synthetic AuxRE re porter genes and effector genes encoding Aux/IAA proteins showed that overexpression of Aux/IAA proteins in carrot protoplasts resulted in s pecific repression of TGTCTC AuxRE reporter gene expression.