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. 2014 Aug 23;3(1):135–145. doi: 10.1002/wdev.126

Figure 2.

Figure 2

LAFL and VAL networks regulate the seed to seedling phase transition. Spatial and temporal patterns of LAFL gene expression are refined by mutual interactions.12–15 Important direct targets of LAFL factors include ( 1) SSP 12,16–18 and LEA genes,19,20 (2) transcription factor genes that control seed specific processes including PEI1,15,21 CUC1,22 BBM,22 WRI122–24 and FLC,15,25 and (3) genes that function in major hormone metabolism and signaling pathways.13,15,22,26–29 AGL15,30,31 PHB/PHV,32 and MYB115/118 33are proposed to act upstream of LAFL network. The LAFL network is repressed by VAL B3 factors and other repressors during seed germination to enable the transition to seedling development. VAL factors play a central role in repression of LAFL network in part by binding to the Sph/RY motif and recruiting an HDAC.10,11,34,35 The interaction of VAL B3 factors with HDAC may be mediated by the co-repressor SNL1.36 PRC2 proteins (CLF/SWN/MEA/EMF2) add H3K27me3 marks to LAFL genes.37,38 Acting in concert with PRC2, PRC1 proteins (LHP1/ EMF1/RING1a-b/BMI1a-b) bind to H3K27me3 marks and deposit H2AK119ub1 to maintain a stable repressed state of LAFL genes.37,39,40 The CHD3 chromatin remodeling factors, PKL and PKR2, can indirectly promote H3K27me3 modification by up-regulating genes encoding PRC2 proteins.41 PKL is also present in the promoter region of LEC1, LEC2 and FUS3 genes that are enriched for H3K27me3.42 RBR can interact with the promoter of ABI3, and is required for establishing H3K27me3 modification by cooperating with PRC2.43,44 The SNF2 chromatin remodeling ATPase, BRM, can repress seed maturation genes by physically interacting with their promoters.45,46 The plant-specific trihelix factor, ASIL1, contributes to repression of LAFL genes by binding to the GT element (CGTGATT).47 miR166 indirectly represses LEC2 transcription by targeting upstream PHB and PHV.32 GA signaling enhances VAL and PKL repression of the LAFL network.10,48 Negative feedback loops: LAFL factors (FUS3 and LEC1) up-regulate VAL1, RING1b, miR166, and PKL.22,24 Black lines with arrows indicate activation, and black lines ending with bars indicate repression. Inferred functions with less experimental evidence are indicated by dashed lines.