HDA9 contributes to cell division–dependent decline in MIR156C. (A) Plant morphology and quantification of the first leaf with abaxial trichomes. Plants were grown for 28 d in long days. A total 20 plants for each genotype were examined. The data for wild-type were the same as in SI Appendix, Fig. S1B. The statistically significant differences are determined by ordinary one-way ANOVA (P < 0.05). (Scale bars, 1.0 cm.) (B) Quantification of leaf length/width ratio. Plants were grown in long days. The ratio of the first, third, fifth, seventh, and ninth leaf was examined. A total 10 plants for each genotype were examined. The data for wild-type were the same as in SI Appendix, Fig. S1C. Error bars show the SD. (C) Quantification of GFP-N7 mRNA levels in the distal region of the pMIR156C:GFP-N7 roots by qRT-PCR. The expression level at 3 DAS is set to 1.0. Two biological replicates were performed. Error bars show the SEM. (D) The level of H3K27ac at the MIR156C locus in wild-type, hda9, and hda6 hda7 hda9 mutant. Two regions (pTSS, transcription start site; pmiR156, the stem-loop region of miR156, [E]) were examined. The distal root regions of 5-d-old seedlings were harvested for ChIP-qPCR assays. The level of H3K27ac in wild-type was set to 1.0. Three biological replicates were performed. Error bars show the SEM. One-way ANOVA was performed followed by Dunnett’s multiple comparison test, *P < 0.05, **P < 0.01, ****P < 0.0001, and ns, not significant. (E) Histone modifications at the MIR156C locus. Wild-type seedlings were grown on vertical 0.5× MS plates. The proximal and distal regions are harvested on days 3 and 7 and subjected to ChIP-seq analyses using anti-H3K27ac and anti-H3K27me3 antibodies. For the FVP experiment, wild-type seedlings were grown on vertical 0.5× MS plates for 3 d and treated with 10 μM FVP for 4 d. The distal regions were then harvested. The black vertical line represents the location of the mature miR156 sequence. The TSS is indicated by the arrow. Two biological replicates were shown by dark and light colors, respectively. The values in square brackets represent normalized read counts.