BLR encodes a homeodomain TF and plays a central role in shoot apical meristem development by affecting meristem activity, phyllotaxis, and floral organ patterning 22. The AP2 paralogs TARGET OF EAT1вЂ“3 (TOE1вЂ“3), SCHNARCHZAPFEN (SNZ), and SCHLAFMUETZE (SMZ) were identified as key repressors of floral transition 20, 21.ДЇloral organ growth and differentiation is further controlled by other types of TFs, including BELLRINGER (BLR) 22, JAGGED (JAG) 23, ETTIN (ETT) 24, 25, and REPRESSOR OF GIBBERELLIC ACID (RGA) 26. Besides this, AP2 was found to regulate meristem maintenance and seed development 17, 19.

AP2 was shown to repress AG expression in the outer floral whorls in Arabidopsis 17 as well as the expression of AG, AP3, and PI orthologs in Petunia 18. All floral homeotic proteins, with the exception of AP2 whose classification as a homeotic factor is under debate 16, encode members of the MADS-domain TF family. Stamen identity is specified by a tetramer that contains AP3, PI, AGAMOUS (AG), and SEP, while carpel identity is determined by a tetramer consisting of AG and SEP proteins 15. In this model, sepals are specified by a complex consisting of AP1 and SEP proteins, while AP1, AP3, PISTILLATA (PI), and SEP form a higher-order complex that determines petal identity. According to the вЂњfloral quartet modelвЂќ, floral homeotic proteins form organ-specific tetrameric protein complexes, and the higher-order interactions are mediated by the redundantly acting SEPALLATA (SEP) proteins (including SEP1, SEP2, SEP3, and SEP4) 14. AP1 and LFY activate floral homeotic genes 13, which then act in a combinational fashion to specify the identities of four different types of floral organs (sepals, petals, stamens, and carpels). The FM identity genes LEAFY ( LFY) 9 and APETALA1 ( AP1) 10 upregulate each otherвЂ™s expression in a positive feedback loop 11, 12, resulting in stable specification of FM identity. Interestingly, SVP has a later role in floral meristem (FM) development together with two positive regulators of flowering time, the MADS-domain proteins SOC1 and AGL24В (ref.

Another flowering repressor protein, SHORT VEGETATIVE PHASE (SVP), is a MADS-domain protein that has roles in temperature responses by forming complexes with FLC and FLM-ОІ, respectively 4, 6, 7. The closely related FLOWERING LOCUS M (FLM) instead mediates the response to changes in ambient temperature 4, 5. The MADS-domain protein FLOWERING LOCUS C (FLC) acts asВ a major floral repressor that is epigenetically downregulated during vernalization. Over the past three decades, key TFs controlling floral transition and flower formation have been identified in Arabidopsis thaliana 1вЂ“ 3. The transition from vegetative to reproductive growth in plants is controlled by the sequential and coordinated activity of transcription factors (TFs) that integrate environmental signals, such as photoperiod, temperature and nutrient status, and endogenous cues such as plant age. Our results provide a valuable resource for studying molecular regulatory processes underlying floral organ specification in plants. We further show that combinatorial DNA-binding of homeotic factors and selected other TFs is predictive of organ-specific patterns of gene expression. Experimental validation of a coherent FFL shows that petal size is controlled by the SEPALLATA3-regulated miR319/TCP4 module. We identify prevalent feed-forward loops (FFLs) mediated by floral homeotic TFs and miRNAs that regulate common targets.

Here, using a combination of genome-wide TF binding, mRNA and miRNA expression data, we reconstruct the dynamic GRN controlling floral meristem development and organ differentiation. In particular, the interconnections of homeotic TFs, microRNAs (miRNAs) and other factors controlling organ initiation and growth have not been studied systematically so far. However, the architecture and theВ function of the gene regulatory network (GRN) controlling floral organ specification is still poorly understood. Floral homeotic transcription factors (TFs) act in a combinatorial manner to specify the organ identities in the flower.

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