Completing the TRB family: newly characterized members show ancient evolutionary origins and distinct localization, yet similar interactions

Abstract

Telomere repeat binding proteins (TRBs) belong to a family of proteins possessing a Myb-like domain which binds to telomeric repeats. Three members of this family (TRB1, TRB2, TRB3) from Arabidopsis thaliana have already been described as associated with terminal telomeric repeats (telomeres) or short interstitial telomeric repeats in gene promoters (telo-boxes). They are also known to interact with several protein complexes: telomerase, Polycomb repressive complex 2 (PRC2) E(z) subunits and the PEAT complex (PWOs-EPCRs-ARIDs-TRBs). Here we characterize two novel members of the TRB family (TRB4 and TRB5). Our wide phylogenetic analyses have shown that TRB proteins evolved in the plant kingdom after the transition to a terrestrial habitat in Streptophyta, and consequently TRBs diversified in seed plants. TRB4-5 share common TRB motifs while differing in several others and seem to have an earlier phylogenetic origin than TRB1-3. Their common Myb-like domains bind long arrays of telomeric repeats in vitro, and we have determined the minimal recognition motif of all TRBs as one telo-box. Our data indicate that despite the distinct localization patterns of TRB1-3 and TRB4-5 in situ, all members of TRB family mutually interact and also bind to telomerase/PRC2/PEAT complexes. Additionally, we have detected novel interactions between TRB4-5 and EMF2 and VRN2, which are Su(z)12 subunits of PRC2.

Telo boxes within the AGAMOUS second intron recruit histone 3 lysine 27 methylation to increase petal number in rose (Rosa chinensis) in response to low temperatures

“…In Arabidopsis, TRBs bind to the telo boxes to recruit the H3K27me3 writer PRC2 complex (Kusova et al, 2023;Zhou et al, 2018). We conducted chromatin immunoprecipitation followed by quantitative PCR (ChIP-qPCR) analysis with an anti-H3K27me3 antibody to assess the chromatin status at the RcAG locus in rose seedlings cultured at 22 or 28°C.…”