# Plant Synthetic Promoters
## 2 Sections of Plant Promoters
### Proximal Promoter  
The proximal promoter, encompassing the region within up to 300 bp upstream from TSS, houses most of the functional cis-active elements required for the proper spatiotemporal or stress-responsive regulation of gene expression (Figure 1) [67; 81; 111; 112; 113]. According to [PERSON] et al., 63% of all _A. thaliana_ cis-active elements are concentrated within a region slightly exceeding the proximal promoter, up to 400 bp upstream from TSS [109]. Also in the peach (_Prunus persica_)cis-active motifs are concentrated within \(-500\) to \(+200\) in relation to TSS [114]. Moreover, the results of [PERSON] et al. clearly show that the preferred localization of AuxRE (TGTSTSB, where S = C or G and B=C, G, or T) lies within the proximal promoter, 250 bp upstream from TSS [115].Furthermore, these cis-active motifs are gathered within conserved cis-regulatory modules (CCRM), enabling interactions between trans-factors bound by neighboring, closely spaced cis-active motifs [67; 113; 116]. [PERSON] et al. suggest that LEC1 interacts with ABA-responsive element binding protein3 (AREB3), basic leucine zipper67 (bZIP67), and ABA-insensitive (ABI3) trans-factorsto regulate various sets of genes controlling morphogenesis, gibberell signaling, photosynthesis, and maturation-related processes during soybean seed development [117]. Similarly, the TaNAC100 trans-factor could orchestrate the expression of starch synthesis genes in wheat [118]. Also, the responsiveness to auxin is mediated not only by a single AuxRE but also by multiple AuxREs. In the composite AuxRE elements associated with auxin response, ABRE-like and Y patch are 5\({}^{\prime}\)-flanking or overlapping AuxRE, whereas the AuxRE-like motif is 3\({}^{\prime}\)-flanking [110].  
The relationship between trans-factor concentration, dimerization efficiency, and affinity to cis-active elements was studied among trans-factors in the CCRM-1 of the _Glu_ gene; the gene is responsible for the biosynthesis of high-molecular-weight glutenin subunits (HMW-GS) [113]. The concentration of the WUSCHEL trans-factor could regulate its predominance as a monomer or dimer through the cooperative binding of corresponding cis-elements, which would increase the prevalence of dimers at lower concentrations, accompanied by increased _CLAVATA3_ gene expression [119].Transcription factor complexes organized within proximal promoters interact with mediator subunits looped towards the RNA polymerase II preinitiation complex, to affect its activity, represented by gene transcription rate (Figure 1) [34]. Among examples of such interactions is the MED25 subunit physically associated with the basic helix-loop-helix transcription factor MYC2 in the promoter regions of MYC2 target genes to positively affect MYC2-regulated gene expression. However, the binding of MED25 to the basic leu zipper transcription factor ABA-insensitive 5 (ABI5) in promoter regions of ABI5 target genes shows a negative effect on ABI5-regulated gene transcription [120]. Moreover, MED18 subunit interacts with SUPPRESSOR OF FRIGIDA4 and ABA-insensitive4 to regulate flowering time and abscisic acid (ABA) responses, respectively [121].