Conservation and divergence within the Arabidopsis TPL/TPR corepressor family

The TOPLESS (TPL) and TOPLESS-RELATED (TPR1-TPR4) corepressors, collectively the Arabidopsis TPL/TPR family, are recruited by client proteins to regulate nearly every major plant regulatory program. Here, we dissect the conservation and divergence between paralogs using a combination of higher-order genetics, transcriptomics, and a synthetic repression assay. TPL, TPR1, and TPR4 were found to act as the primary repressors for many pathways (including rosette leaf number, flowering time, immune responses, and auxin-regulated root architecture), while TPR2 and TPR3 played a lesser or sometimes opposite regulatory role. Natural variation among the five paralogs in the EAR-binding pocket subdivided the family into three subtypes: TPL/TPR1, TPR2/TPR3 and TPR4, and this variation at least partially explained observed differences between mutant phenotypes. In addition, cell-type-specific expression of EAR-containing effectors were used to tune root architecture, providing a possible route to engineering other TPL/TPR-regulated pathways. These results suggest a model where the TPL/TPR family balances robustness under stable conditions with the need for flexibility during cell fate transitions or stress responses.