Figure 7.

STK binds to the STM locus. A, B) H3K9/14ac ChIP-qPCR of STM TSS (A) and of a distal promoter region (−2 kb) (B) in the wild type, hda19-3, stk, and stk shp1 shp2 mutants. The pattern of acetylation at the STM locus is similar among the different mutant genotypes. Graphs show the mean ± SD value of enrichment among three independent biological replicates of the H3K9/14ac ChIP-qPCR experiment performed on wild-type, hda19-3, stk, and stk shp1 shp2 flowers. Student's t-test, **P-value < 0.01. ***P-value < 0.001. C) Regions of the STM locus tested by anti-GFP ChIP-qPCR in wild-type and pSTK::STK-GFP flowers. Triangles mark CaRG boxes detected by AthaMap (Steffens et al. 2004) while the bar marks the TSS region of STM. D) ChIP-qPCR to test binding of STK (pSTK::STK-GFP) to the promoter, TSS, first intron, and second intron of STM. VDD is a known direct target of STK, so it was used as positive control. Graph shows the mean ± SD enrichment value among four independent biological replicates of the anti-GFP ChIP-qPCR experiment. Student's t-test, *P-value < 0.05. **P-value < 0.01. E) Model of the regulation of STM expression in the CMM involving HDA19 and STK. Until stage 7, the expression of STM in the CMM is high due to the presence of acetylated histones in association with the STM locus. At stages 8 to 9, when the CMM starts producing the ReT organs, HDA19 deacetylates the histones associated with the STM locus, leading to its downregulation and thereby allowing the formation of OP and TT. Direct binding of STK to the STM locus facilitates the action of HDA19, potentially by generating multimeric complexes involved in HDA19 binding and stabilization to the STM locus. Abbreviations and symbols: CMM, carpel margin meristem; mr, medial ridge; OP, Ovule primordia; TF, transcriptional factor; Ac, acetyl group.