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Fig. 2 | BMC Plant Biology

Fig. 2

From: Gene regulatory network and abundant genetic variation play critical roles in heading stage of polyploidy wheat

Fig. 2

Schematic summary of the wheat heading stage regulatory network. Before vernalization, VRN2 competes with other CCT-domain proteins (like CO2) to interact with NF-Y transcription factors to inhibit the transcription of VRN3. Secondly, TaGRP2 can directly bind to this binding site of VRN1 to prevent transcript accumulation. Thirdly, TaVRT-2 can directly bind to the CArG box of the TaVRN1 promoter in vivo to inhibit its activity, and this inhibition is enhanced by VRN2. Following vernalization, VRN1 transcripts were enhanced by changing the ratio of H3K4me3 to active gene transcription. However, the expression level of VRN2 decreases after vernalization to release VRN3, then they can move from the leaves to the apices via the phloem. In the stem apical meristem, the VRN3 protein then forms a functional protein complex with TaFDL to bind the CArG box domain in the promoter of VRN1 in vitro, leading to transcriptional activation. Meanwhile, phosphorylated VER2 (VER2-P) transfers into the nucleus and then gathers in the shoot tips and young leaves, physically interacting with the RNA-binding protein TaGRP2, which is O-GlcNAc-modified,to decrease the inhibitory action on VRN1 expression. Furthermore, the expression levels of TaVRT2 and VRN2 decrease, and VRN1 gradually accumulates. Finally, the expression level of VRN1 is significantly enhanced to accelerate flowering. VRN-D4, as a duplicated copy of VRN1, expresses in the leaves and accumulates after prolonged exposure to low temperature, and can directly or indirectly influence VRN1 among the three vernalization genes the earliest, but has less effect than Vrn-A1. Long-day (LD) induces the accumulation of physiologically active Pfr (PHYB:PHYC heterodimers and PHYC:PHYC homodimers) and then activates the transcription of PPD1 and circadian clock output genes CO2/TaDH1, and the VRN3 transcript can be promoted by PPD1 and CO2. However, PPD1 is inhibited by WPCL1, which is a flowering negative regulator, but the interaction mechanism of these two genes is unknown. TaGI, which is controlled by the circadian clock under a light/dark cycle, works on the upstream of CO and produces a bulky protein complex with other suspected proteins, binding to the critical region in the CO gene promoter to induce its transcription. Eps genes work throughout wheat growth and development via an unknown pathway, Green arrows represent promotion, red arrows represent inhibition in the signal pathway

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