1. microRNA 156 Presentation by: Ansuman sahoo Roll: y1011009 Plant Developmental Biology Class

2. Background MicroRNAs (miRNAs) are small, single- stranded RNAs, which down-regulate their target genes through the cleavage of mRNAs, translational repression or transcriptional inhibition These generally regulate the level of transcription factors, Hormones etc. and thus developmental timing as well as position.

3. Developmental Phages Germination Seedling Emergence of Vegetative leaves Adult Phage Floral Induction miR156

4. miRNA156 is conserved in plant kingdom

5. miR156 encoded by six or more MIR genes in Arabidopsis

6. Developmental expression of Arabidopsis miRNAs Se: seedling L: Leaves St: Stem F: Flower Si: Siliques

7. miR156 overexpression prolongs juvenile phase in Arabidopsis

8. miR156 targets SPL genes, promoters of phase change miR156SPL ORF 3’ UTR Promoter SPL3 The SPL genes are a family of transcription factors that are miR156 targets. In wild-type plants, miR156 expression decreases with plant age, allowing SPL to accumulate and promote phase change. miR156 binding site

9. Link between miR156 & miR172 miR156miR172 SPL9/10 TOE1 & TOE2 Downregulation of TOE1 and TOE2 change the phage from vegetative to reproductive

10. We show here that DELLA directly binds to microRNA156 (miR156)- targeted SQUAMOSA PROMOTER BINDING–LIKE (SPL) transcription factors, which promote flowering by activating miR172 and MADS box genes. The interaction between DELLA and SPL interferes with SPL transcriptional activity and consequently delays floral transition through inactivating miR172 in leaves and MADS box genes at shoot apex under long-day conditions or through repressing MADS box genes at the shoot apex under short-day conditions

11. GA signaling pathway Low GA No transcription GA receptor DELLA protein SPL GA SPL DELLA High GA Transcription of miR172 Flowering Proteolysis DELLA proteins inhibit growth, in part through blocking transcription. GA triggers DELLA protein proteolysis. Reprinted from Davière, J.-M., de Lucas, M., and Prat, S. (2008) Transcription factor interaction: a central step in DELLA function. Curr. Opin. Genet. Devel. 18: 295–303.with permission from Elsevier 295–303