Both sense and antisense RNAs are targets for the sense transgene-induced posttranscriptional silencing mechanism

Two stable transgenic tobacco lines were obtained as segregants from a prim ary transformant. Plants homozygous for a T-DNA inverted repeat locus (HOlo 1) showed posttranscriptional gene silencing (PTGS) of the neomycin phospho transferase II (nptII) transgenes, whereas HOlo2 plants, homozygous for a s ingle T-DNA insert, expressed the nptII genes normally. Transient expressio n of nptII genes newly introduced into leaves of both the HOlo2 and nptII-s ilenced HOlo1 plants was downregulated only in the silenced background. Dif ferent chimeric beta-glucuronidase (gus) genes with parts of the nptII tran sgene inserted in sense or antisense orientation into the 3'-untranslated r egion, which encoded transcripts that had homology or complementarity to np tII transcripts, showed reduced transient expression specifically in npII-s ilenced tissue. Therefore, we conclude that RNAs of both polarities are tar gets for PTGS-induced RNA degradation, which supports the notion that doubl e-stranded RNA acts as an inducing signal for silencing.