Abstract
Gibberellins (GAs) are essential regulators of many aspects of plant development. GA 3-oxidase catalyzes the final step of the biosynthetic pathway to produce the active GA. The expression of AtGA3ox1 (GA4) encoding GA 3-oxidase is regulated by GA levels in a feedback manner. To understand the molecular mechanism of feedback regulation, we have identified a cis-acting sequence responsible for GA-negative feedback of AtGA3ox1. Furthermore, we isolated an AT-hook protein AGF1 as a DNA-binding protein for the cis-acting sequence. The mutation in the cis-acting sequence abolished both GA-negative feedback and AGF1 binding. The expression of AGF1 is not regulated by GA levels. This suggested an involvement of post-transcriptional and/or post-translational modification of the transcription factor. We have identified Zn finger protein ZAF1 as an AGF binding protein by a yeast two-hybrid screen. In vitro pull-down assay shows that ZAF1 specifically binds to AGF1 and its binding is direct.
