Zygote/2-celled proembryo specific protein TaMAB2 is involved in proteosomal degradation of translation initiation factors via a cytoskeleton related mechanism

A family of MATH-BTB proteins is known to act as substrate-specific adaptors of CUL3-based E3 ligases in the ubiquitin proteasome pathway. The BTB domain binds a CUL3 scaffold protein and the less conserved MATH domain targets a highly diverse collection of substrate proteins to promote their ubiquitination and subsequent degradation. Among plants, a significant expansion of the MATH-BTB family occurred in grasses. Here, we functionally describe TaMAB2, a wheat MATH-BTB protein expressed exclusively in the zygote and two-celled proembryo. The overexpression of TaMAB2 in Arabidopsis plants provoked microtubular bundling and re-orientation together with retarded growth. In model BY-2 cells, TaMAB2 showed a microtubule and a ubiquitin-related localization which together with direct interaction with CUL3 pointed out its function in targeting specific substrates for ubiquitin-dependent degradation. Results of protein interaction analyses indicated eukaryotic translation initiation factors 3 and 4 as the most likely substrates of TaMAB2, while the interaction with cytoskeletal element, particularly actin 11 hints at the possible TaMAB2 mediated intreplay between cytoskeleton and translation initiation machinery during the first division of the zygote.