Principle of interactions between GFP-COP1 transgenes and the COP1 endogene . The symbols next to the COP1 endogene represent dark-grown seedling and light-grown adult phenotypes. (A) E82 causes dominant transgene silencing and COP1 endogene cosuppression by PTGS. Note however that the cop1-like seedling phenotype is restricted to homozygous plants. (B) L91 causes homozygosity dependent transgene silencing and endogene cosuppression by PTGS. (C) C73 plants of the T3 generation and beyond are transcriptionally silenced and do not display endogene cosuppression. (D) C73 trans-silences E82 and L91 by TGS and thus suppresses PTGS by the E82 and L91 target loci.