title: Expression of the floral repressor miRNA156 is positively regulated by the AGAMOUS-like proteins AGL15 and AGL18.
abstract: The regulation of flowering time has crucial implications for plant fitness. MicroRNA156 (miR156) represses the floral transition in Arabidopsis thaliana, but the mechanisms regulating its transcription remain unclear. Here, we show that two AGAMOUS-like proteins, AGL15 and AGL18, act as positive regulators of the expression of MIR156. Small RNA northern blot analysis revealed a significant decrease in the levels of mature miR156 in agl15 agl18 double mutants, but not in the single mutants, suggesting that AGL15 and AGL18 co-regulate miR156 expression. Histochemical analysis further indicated that the double mutants showed a reduction in MIR156 promoter strength. The double mutants also showed reduced abundance of pri-miR156a and pri-miR156c, two of the primary transcripts from MIR156 genes. Electrophoretic mobility shift assays demonstrated that AGL15 directly associated with the CArG motifs in the MIR156a/c promoters. AGL18 did not show binding affinity to the CArG motifs, but pull-down and yeast two-hybrid assays showed that AGL18 forms a heterodimer with AGL15. GFP reporter assays and bimolecular fluorescence complementation (BiFC) showed that AGL15 and AGL18 co-localize in the nucleus and confirmed their in vivo interaction. Overexpression of miR156 did not affect the levels of AGL15 and AGL18 transcripts. Taking these data together, we present a model for the transcriptional regulation of MIR156. In this model, AGL15 and AGL18 may form a complex along with other proteins, and bind to the CArG motifs of the promoters of MIR156 to activate the MIR156 expression.
authors: Creative Research Initiatives, Department of Life Sciences, Korea University, Seoul 136-701, Korea.
authors: Phanu
authors: P
authors: Serivichyaswat
authors: Creative Research Initiatives, Department of Life Sciences, Korea University, Seoul 136-701, Korea.
authors: Hak-Seung
authors: HS
authors: Ryu
authors: Creative Research Initiatives, Department of Life Sciences, Korea University, Seoul 136-701, Korea.
authors: Wanhui
authors: W
authors: Kim
authors: Creative Research Initiatives, Department of Life Sciences, Korea University, Seoul 136-701, Korea.
authors: Soonkap
authors: S
authors: Kim
authors: Creative Research Initiatives, Department of Life Sciences, Korea University, Seoul 136-701, Korea.
authors: Kyung Sook
authors: KS
authors: Chung
authors: Creative Research Initiatives, Department of Life Sciences, Korea University, Seoul 136-701, Korea.
authors: Jae Joon
authors: JJ
authors: Kim
authors: Creative Research Initiatives, Department of Life Sciences, Korea University, Seoul 136-701, Korea.
authors: Ji Hoon
authors: JH
authors: Ahn
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000502:physiology*; D001483:Base Sequence; D018506:Gene Expression Regulation, Plant; D026161:MADS Domain Proteins / Q000502:physiology*; D035683:MicroRNAs / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D034622:RNA Interference
chemical_list: C522473:AGL15 protein, Arabidopsis; C522474:AGL18 protein, Arabidopsis; D029681:Arabidopsis Proteins; D026161:MADS Domain Proteins; D035683:MicroRNAs; C559759:Mirn156 microRNA, Arabidopsis
keywords: AGAMOUS-like 15; AGAMOUS-like 18; CArG motifs; floral transition; miRNA156