title: MicroRNA159 can act as a switch or tuning microRNA independently of its abundance in Arabidopsis.
abstract: The efficacy of gene silencing by plant microRNAs (miRNAs) is generally assumed to be predominantly determined by their abundance. In Arabidopsis the highly abundant miRNA, miR159, acts as a molecular "switch" in vegetative tissues completely silencing the expression of two GAMYB-like genes, MYB33 and MYB65. Here, we show that miR159 has a diminished silencing efficacy in the seed. Using reporter gene constructs, we determined that MIR159 and MYB33 are co-transcribed in the aleurone and embryo of germinating seeds. However in contrast to vegetative tissues, MYB33 is not completely silenced. Instead, miR159 appears to shape the spatio-temporal expression pattern of MYB33 during seed germination. Transcript profiling in a time course during seed germination in wild-type and a mir159 mutant in which miR159 is almost absent, revealed that transcript levels of the GAMYB-like genes were similar between these two genotypes during germination, but much higher in the mir159 mutant once germination had completed. This attenuation in the silencing of the GAMYB-like genes was not explained by a decrease in mature miR159 levels, which remained constant at all time points during seed germination. We propose that miR159 acts as a tuner of GAMYB-like levels in Arabidopsis germinating seeds and that the activity of this miRNA is attenuated in the seed compared to vegetative tissues. This implies that the efficacy of miRNA-mediated silencing is not solely determined by miRNA abundance and target transcript levels, but is being determined through additional mechanisms.
authors.affiliation: Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia.
authors.forename: Maria M
authors.initials: MM
authors.lastname: Alonso-Peral
authors.forename: Cheng
authors.initials: C
authors.lastname: Sun
authors.forename: Anthony A
authors.initials: AA
authors.lastname: Millar
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D020868:Gene Silencing; D017930:Genes, Reporter; D018525:Germination / Q000235:genetics; D035683:MicroRNAs / Q000378:metabolism / Q000502:physiology*; D012639:Seeds / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C577006:MIRN159 microRNA, Arabidopsis; D035683:MicroRNAs; C577007:Myb33 protein, Arabidopsis; D014157:Transcription Factors