This invention relates to constructs for the conditional or regulated expression or excision of transgenes in plants using site-specific recombinase systems. The constructs comprise a variety of constitutive, inducible, tissue specific or developmental stage-specific promoters operably linked to either a transgene or the elements of one or more site-specific recombinase system. By matching promoters, responsive to various inducers, plant tissues or plant developmental states with the recombinase systems, stop fragments and transgenes, virtually any trait may be expressed or excised at any plant development stage or in any plant generation.