SUMOylation is Required for Function of the Caenorhabditis elegans T-box Transcription Factor, TBX-2

T-box proteins are important dose-dependent developmental regulators of multicellular organisms, but little information exists regarding regulation of T-box factors in vivo. We are studying C. elegans TBX-2 to elucidate mechanisms controlling T-box factor function and regulation in animals. One way T-box factors may be regulated is through post-translational SUMOylation. SUMOylation is required for TBX-2 function. TBX-2 is SUMOylated in vitro and the minimal interaction domain between TBX-2 and SUMO-pathway components UBC-9 and GEI-17 was mapped. These interaction domains, TBX-2 LKIE and VKKE, match the classical SUMOylation consensus (ψKXD/E), and are necessary for SUMOylation of TBX-2. These interaction domains are likely UBC-9 and GEI-17 recruitment sites which may facilitate SUMOylation at other sites. TBX-2 and the C. elegans SUMO peptide, SMO-1, interact in vivo. Nuclear distribution and localization of the TBX-2/SMO-1 protein complex is dependent on the TBX-2 LKIE/VKKE interaction domain. UBC-9 depletion causes visual intensification of the subnuclear TBX-2 LKIE/VKKE mutant/SMO-1 BiFC signal. In addition, evidence demonstrating a strong genetic interaction between tbx-2 and ubc-9 and between tbx-2 and smo-1 in worms is provided.