DEX Complementation: What is it?

[Graeme Kirk]

I will be starting in the world of Arabidopsis research in a couple of
months. I have heard of a complemetation mechanism using Dexamethasone.
Sorry but that is about all I know. Could somone PLEASE explain?
I have searched for references and have only found Dex referenced as a
system for inducible gene expression  The complementation thing said it
would restore fertility to mutants.

I hope to hear soon.
Thanks
Graeme