Transformation efficiency and transgene expression level in marker-free RDR6-knockdown transgenic tobacco plants

Abstract

RNA silencing is a sequence-specific form of epigenetic regulation that targets invasive nucleic acids. RNA-dependent RNA polymerase6 (RDR6) converts target RNA molecules, such as transgene transcripts, into double-stranded RNAs (dsRNAs) during posttranscriptional gene silencing (PTGS). Then, these dsRNAs are processed into small RNAs that guide sequence-specific RNA degradation. T-DNA-derived small RNAs are generated during the transfer of T-DNA from Agrobacterium to plant cells and compromise the function of the genes in the T-DNA. In the present study, we produced selection-marker-free transgenic tobacco plants using the MAT vector system, and expression of the tobacco RDR6 gene (NtRDR6) was suppressed using inverted-repeat-induced PTGS. Reduced expression of the NtRDR6 gene improved the transient expression of the transgene in the agroinfiltrated leaves and enhanced the production of hairy roots after infection with Agrobacterium containing a root-inducing T-DNA. The expression level of the sense transgene was determined in individual hairy roots, and knockdown of the NtRDR6 gene did not affect the distribution of the expression levels in individual transformants. These results indicate that NtRDR6 partially inhibited T-DNA function during T-DNA transfer but did not affect the expression of the transgene in stable transformants, except in transformants showing sense-transgene-induced PTGS.