Species-specificity of rRNA gene transcription in plants manifested as a switch in RNA polymerase specificity.
Rapid evolution of ribosomal RNA (rRNA) gene promoters often prevents their recognition in a foreign species. Unlike animal systems, we show that foreign plant rRNA gene promoters are recognized in an alien species, but tend to program transcription by a different polymerase. In plants, RNA polymerase I transcripts initiate at a TATATA element (+1 is underlined) important for promoter strength and start-site selection. However, transcripts initiate from +32 following transfection of a tomato promoter into Arabidopsis. The rRNA gene promoter of a more closely related species, Brassica oleracea, programs both +1 and +29 transcription. A point mutation at +2 improving the identity between the Brassica and Arabidopsis promoters increases +1 transcription, indicating a role for the initiator element in species-specificity. Brassica +29 transcripts can be translated to express a luciferase reporter gene, implicating RNA polymerase II. TATA mutations that disrupt TATA-binding protein (TBP) interactions inhibit +29 transcription and luciferase expression. Co-expressed TBP proteins bearing compensatory mutations restore +29 transcription and luciferase activity, suggesting a direct TBP-TATA interaction. Importantly, +1 transcription is unaffected by the TATA mutations, suggesting that in the context of pol I recognition, the TATA-containing initiator element serves a function other than TBP binding.
Doelling
J H
JH
Biology Department, Washington University, St Louis, MO 63130, USA.
Pikaard
C S
CS
D017360:Arabidopsis / Q000235:genetics; D001483:Base Sequence; D001937:Brassica / Q000235:genetics; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D015870:Gene Expression; D008156:Luciferases / Q000378:metabolism; D018551:Solanum lycopersicum / Q000235:genetics; D008969:Molecular Sequence Data; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D011523:Protoplasts; D012318:RNA Polymerase I / Q000378:metabolism*; D012319:RNA Polymerase II / Q000378:metabolism*; D018749:RNA, Plant / Q000235:genetics*; D012335:RNA, Ribosomal / Q000737:chemistry / Q000235:genetics*; D013045:Species Specificity; D016385:TATA Box; D014158:Transcription, Genetic; D014162:Transfection
D018749:RNA, Plant; D012335:RNA, Ribosomal; D008156:Luciferases; D012319:RNA Polymerase II; D012321:DNA-Directed RNA Polymerases; D012318:RNA Polymerase I