Fig. 7: Functional divergence of HD-ZIPIII proteins is driven by their START domains which convert a single network architecture into paralog-specific regulons.
From: START domains generate paralog-specific regulons from a single network architecture
a The rev-6 mutant has a strong floral termination phenotype66. The pREV:REV transgene fully complements the rev-6 mutant phenotype as plants appear wildtype (Ler), whereas the pREV:CNA transgene does not. The majority of primary transformants carrying a pREV:CNA-AtREV transgene appear wildtype indicating near-complete rescue of the rev-6 mutant phenotype. b Quantification of rev-6 complementation (measured as percentage of floral termination in lateral shoots). Data is presented as a box and whiskers plot using Tukey whiskers. Statistics are against the Ler wildtype in all cases except the red asterisks which are compared to pREV:CNA. * - p-value = 7.7 × 10−4, ** − 9.3 × 10−7, *** - p-value ≤ 2.78 × 10−11, two-way paired Student’s t-test. n = 24, 25, 16, 30, and 36 primary transformants scored per genotype (left to right). c HD-ZIPIII TF paralog divergence through differential regulation of mutually bound genes. In this simplified model, two members of a TF family bind a common set of genes. A given gene could be regulated by both TFs (i.e. Gene 3) or unaffected by both TFs (i.e. Gene 4). Alternatively, a gene could be uniquely regulated by one of the two TFs (Gene 1 vs Gene 2) generating paralog-specific regulatory outcomes from a commonly bound genetic network. Line legend: purple (regulated by both paralogs), black (regulated by neither paralog), red (regulated only by paralog A), blue (regulated only by paralog B). d Speculative, non-mutually exclusive regulatory mechanisms occurring at shared binding sites (orange DNA). Inputs integrated via START domains could include ligands (purple), post-translational modifications (PTMs; brown), and protein co-factors such as other TFs, chromatin remodelers, or subunits of the general transcriptional machinery (blue). Functional consequences for gene expression may also depend on histone modifications, DNA methylation, degree of chromatin compaction, or other aspects of chromatin context.
