RESUMEN
In animals, RNA polymerase II initiates transcription bidirectionally from gene promoters to produce pre-mRNAs on the forward strand and promoter upstream transcripts (PROMPTs) on the reverse strand. PROMPTs are degraded by the nuclear exosome. Previous studies based on nascent RNA approaches concluded that Arabidopsis (Arabidopsis thaliana) does not produce PROMPTs. Here, we used steady-state RNA sequencing in mutants defective in nuclear RNA decay including the exosome to reassess the existence of Arabidopsis PROMPTs. While they are rare, we identified â¼100 cases of exosome-sensitive PROMPTs in Arabidopsis. Such PROMPTs are sources of small interfering RNAs in exosome-deficient mutants, perhaps explaining why plants have evolved mechanisms to suppress PROMPTs. In addition, we found â¼200 long, unspliced and exosome-sensitive antisense RNAs that arise from transcription start sites within parts of the genome encoding 3'-untranslated regions on the sense strand. The previously characterized noncoding RNA that regulates expression of the key seed dormancy regulator, DELAY OF GERMINATION1, is a typical representative of this class of RNAs. Transcription factor genes are overrepresented among loci with exosome-sensitive antisense RNAs, suggesting a potential for widespread control of gene expression via this class of noncoding RNAs. Lastly, we assess the use of alternative promoters in Arabidopsis and compare the accuracy of existing TSS annotations.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Mutación , Regiones Promotoras Genéticas/genética , Regiones Promotoras Genéticas/fisiología , ARN sin Sentido/genética , ARN sin Sentido/metabolismo , ARN no Traducido/genética , ARN no Traducido/metabolismo , Semillas/genética , Semillas/metabolismoRESUMEN
Small RNA-guided endonucleolysis ("slicing") of target mRNA is the signature biochemical activity underlying many RNA silencing phenomena. The catalytic slicer activity resides in Argonaute (AGO) proteins. Here, we present two protocols to detect microRNA-guided slicer activity of AGO1 immunopurified from Arabidopsis tissues. The first uses radioactive, cap-labeled RNA substrates produced by in vitro transcription of RNA fragments corresponding to endogenous target sites flanked by 100-200 nucleotides of target sequence. The second protocol uses similarly designed but shorter (around 50 nt) fluorescently labeled RNA. Advantages and disadvantages of the two setups are also discussed.
