Transcriptional and Posttranscriptional Regulation of Dormancy-Associated Gene Expression by Afterripening in Wild Oat

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Abstract
To investigate whether the afterripening-induced changes in gene expression are at the transcriptional or posttranscriptional level in wild oat (Avena fatua) seeds, we chose four dormancy-associated genes to estimate their relative transcription activities and the stability of their corresponding transcripts in afterripened and dormant embryos. The transcription activities for those genes were 1.5 to 7 times higher in dormant embryos than in afterripened embryos 24 h after incubation, as determined by nuclear run-on assays. The half-lives of the transcripts in afterripened and dormant embryos were estimated by the use of actinomycin D. The application of actinomycin D resulted in the stabilization of the transcripts. Nevertheless, the results indicated that the half-lives of the transcripts were much greater in dormant embryos than in afterripened embryos. Considering the great differences in the steady-state levels and the half-lives of the mRNAs, and the relatively small differences in transcription activities of the genes between afterripened and dormant embryos, we conclude that afterripening regulates the expression of dormancy-associated genes in excised embryos mainly at the posttranscriptional level and that transcriptional control plays a minor role.