Fig. 1

Common origin of heterodimerizing TALE homeobox TFs. Hypothesized homodimerizing proto-TALE protein (top) duplicated before the eukaryotic radiations into animals/fungi/amoebae vs. algae/plants. Lineage-specific diversification soon followed, generating heterodimeric configurations distinct at the phylum-level. (Left) Each lineage possesses one or two classes of potential heterodimeric TALEs, which are summarized onto the eukaryotic phylogeny. A representative species name is given for each analyzed lineage. (Right) Summary of TALE configurations, coupling members of the PBC/PBX/GLX group that shares PBC-homology domains and of the MEIS/KNOX group that shows homology in the KN-A/B domains N-terminal to the homeodomain. Lightly shaded boxes depict homology domains, whose names are provided above. Open areas in the domain boxes indicate the absence of MEINOX-motif for PBX-Red, KN-A for KNOX-Red1 and ELK for KNOX-Red2. Colored vertical lines in the HD indicate two shared introns at 44/45 (orange over “H” in HD) and 48(2/3) (blue over “D” in HD), whose alternating existence between the two groups suggests independent diversification of TALE heterodimerization. HD: Homeodomain; PBL-C: PBL-Chloro; PBL-R: PBL-Red