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Transgenic cassava resistance to African cassava mosaic virus is enhanced by viral DNA-A bidirectional promoter-derived siRNAs

Vanderschuren, Hervé, Akbergenov, Rashid, Pooggin, Mikhail M., Hohn, Thomas, Gruissem, Wilhelm, Zhang, Peng
Plant molecular biology 2007 v.64 no.5 pp. 549-557
African cassava mosaic virus, RNA interference, cassava, cells, disease resistance, double-stranded RNA, leaves, promoter regions, single-stranded DNA, small interfering RNA, transgenic plants, viruses
Expression of double-stranded RNA (dsRNA) homologous to virus sequences can effectively interfere with RNA virus infection in plant cells by triggering RNA silencing. Here we applied this approach against a DNA virus, African cassava mosaic virus (ACMV), in its natural host cassava. Transgenic cassava plants were developed to express small interfering RNAs (siRNA) from a CaMV 35S promoter-controlled, intron-containing dsRNA cognate to the common region-containing bidirectional promoter of ACMV DNA-A. In two of three independent transgenic lines, accelerated plant recovery from ACMV-NOg infection was observed, which correlates with the presence of transgene-derived siRNAs 21–24 nt in length. Overall, cassava mosaic disease symptoms were dramatically attenuated in these two lines and less viral DNA accumulation was detected in their leaves than in those of wild-type plants. In a transient replication assay using leaf disks from the two transgenic lines, strongly reduced accumulation of viral single-stranded DNA was observed. Our study suggests that a natural RNA silencing mechanism targeting DNA viruses through production of virus-derived siRNAs is turned on earlier and more efficiently in transgenic plants expressing dsRNA cognate to the viral promoter and common region.