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Báo cáo khoa học: Loss of sense transgene-induced post-transcriptional gene silencing by sequential introduction of the same transgene sequences in tobacco

RNA silencing is an epigenetic inhibition of gene expression and is guided by small interfering RNAs. Sense transgene-induced post-transcriptional gene silencing (S-PTGS) occurs in a portion of a transgenic plant popula-tion. When a sense transgene encoding a tobacco endoplasmic reticulum x-3 fatty acid desaturase (NtFAD3) was introduced into tobacco plants, an S-PTGS line, S44, was obtained. | ỊFEBS Journal Loss of sense transgene-induced post-transcriptional gene silencing by sequential introduction of the same transgene sequences in tobacco Sayaka Hirai1 Kouta Takahashi2 Tomomi Abiko3 and Hiroaki Kodama1 1 Graduate Schoolof Horticulture Chiba University Japan 2 Graduate Schoolof Science and Technology Chiba University Japan 3 Faculty of Horticulture Chiba University Japan Keywords fatty acid desaturase post-transcriptional gene silencing RNA-directed DNA methylation threshold a-linolenic acid Correspondence H. Kodama Graduate Schoolof Horticulture Chiba University 648 Matsudo Chiba 271-8510 Japan Fax 81 43 290 3942 Tel 81 43 290 3942 E-mail kodama@faculty.chiba-u.jp Received 31 October 2009 revised 23 January 2010 accepted 26 January 2010 doi 10.1111 j.1742-4658.2010.07591.x RNA silencing is an epigenetic inhibition of gene expression and is guided by small interfering RNAs. Sense transgene-induced post-transcriptional gene silencing S-PTGS occurs in a portion of a transgenic plant population. When a sense transgene encoding a tobacco endoplasmic reticulum ro-3 fatty acid desaturase NtFAD3 was introduced into tobacco plants an S-PTGS line S44 was obtained. Introduction of another copy of the NtFAD3 transgene into S44 plants caused a phenotypic change from S-PTGS to overexpression. Because this change was associated with the methylation of the promoter sequences of the transgene reduced transcriptional activity may abolish S-PTGS and residual transcription of the sense transgene may account for the overexpression. To clarify whether RNA-directed DNA methylation RdDM can repress the transcriptional activity of the S44 transgene locus we introduced several RdDM constructs targeting the transgene promoter. An RdDM construct harboring a 200-bp-long fragment of promoter sequences efficiently abrogated the generation of NtFAD3 small interfering RNAs in S44 plants. Transcription of the transgene was partially repressed but the resulting NtFAD3 mRNAs .