RNA-Mediated RNA Degradation and Chalcone Synthase A Silencing in Petunia

Transgenic Petunia plants with a chsA coding sequence under the control of a 35S promoter sometimes lose endogene and transgene chalcone synthase activity and purple flower pigment through posttranscriptional chsA RNA degradation. In these plants, shorter poly(A)+ and poly(A)- chsA RNAs are found, and a 3' end-specific RNA fragment from the endogene is more resistant to degradation. The termini of this RNA fragment are located in a region of complementarity between the chsA 3' coding region and its 3' untranslated region. Equivalent chsA RNA fragments remain in the white flower tissue of a nontransgenic Petunia variety. We present a model involving cycles of RNA-RNA pairing between complementary sequences followed by endonucleolytic RNA cleavages to describe how RNA degradation is likely to be promoted.