[Genstructure] GUS/GFP tagged promoters or GUS/GFP fusion proteins

[Gwendolyn]

I am a Genetics students and I've got the following doubt:

I read some papers that described experiments where plants were
transformed with both a GUS and a GFP tagged promoter (same promoter in
both cases) or with a GUS and a GFP fusion protein (same protein in
both cases). Why is it that two different reporter constructs  were
used for transformation? Perhaps because there is always the
possibility that GFP will not fluoresce (due to tagging/fusion), or
that the glucuronidase gene will not be (properly) transcribed, due to
the same reasons?

Cheers

Gwen