TOPLESS co-repressor interactions and their evolutionary conservation in plants

Abstract

Large-scale protein-protein interaction studies recently demonstrated that the Arabidopsis TPL/TPR family of transcriptional co-repressors is involved in a broad range of developmental processes. TPL/TPRs predominantly interact with transcription factors that contain repression domain (RD) sequences. Interestingly, RDs reported in the literature are quite diverse in sequence, yet TPL/TPRs interact with proteins containing all of the known motifs. These data lead us to conclude that the TPL/TPRs act as general repressors of gene transcription in plants. To investigate this further, we examined interactions between TPL/TPR proteins encoded by the moss Physcomitrella patens genome and components of the auxin signaling pathway. As in Arabidopsis, moss TPL proteins interact with AUX/IAA and ARF proteins, suggesting that they act in both forms of ARF-mediated transcriptional repression. These data suggest that the involvement of TPL in auxin signaling has been conserved across evolution, since mosses and angiosperms diverged approximately 450 million years ago.

Figure 1.

Phylogenetic relationship of Arabidopsis and moss TPL and LUG proteins. An UPGMA tree, showing the relationships among putative TPL and LUG family proteins from Arabidopsis and P. patens, was generated from ClustalW alignments of full-length proteins using the MacVector software suite. Arabidopsis proteins are highlighted in orange, and P. patens proteins in green. The TPL/TPR and LUG/LUH clades are highlighted. Note that the moss TPL sequences (PpTPL1 and PpTPL2) group with the Arabidopsis TPL, TPR1 and TPR4 proteins, suggesting that this might be the ancestral clade and that the TPR2/TPR3 clade diverged later in the angiosperms, or that the TPR2/TPR3 genes were lost from the moss genome. AtTPL, At1g15750; AtTPR1, At1g80490; AtTPR2, At3g16830; AtTPR3, At5g27030; AtTPR4, At3g15880; AtTPL-like, At2g25420; AtLUG, At4g32551; AtLUH, At2g32700; PpTPL1, Pp1s99_260V6.1; PpTPL2, Pp1s316_34V6.1; PpLUG1, Pp1s371_17V6.1; PpLUG2, predicted from Pp1s371_10V6.1 and Pp1s371_13V6.1; PpLUG3, Pp1s45_33F3.1; PpLUG4, Phypa_162589.

Figure 2.

Protein-protein interactions between moss TPL proteins and components of the auxin signaling pathway. Interactions were tested between PpTPL1/2 bait proteins and moss AUX/IAA or ARF prey proteins in yeast two-hybrid assays. Yeast containing the bait and prey constructs were plated on media that selects for protein-protein interactions (minimal media minus histidine + 2.5mM 3-AT; -His) or control media without selection (+His). Yeast growth in the –His row indicates interaction between the bait and prey proteins listed at the top of the figure. Negative controls for interactions, a moss ARF protein lacking a repression domain (RD) are indicated (-ve). Putative RD sequences present in the appropriate AUX/IAA or ARF protein are listed along the bottom of the panel. Mutated RD residues are underlined. PpTPL1, Pp1s99_260V6.1; PpTPL2, Pp1s316_34V6.1; PpIAA1a, AB061222; PpIAA1b, Pp1s184_21V6.1; PpIAA2, Pp1s73_11V6.1; PpARFa, Pp1s14_392V6.1; PpARFe, Pp1s339_47V6.1; PpARFf, Pp1s279_9V6.1