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AtBPM1 protein interacts with components of RNA- directed DNA methylation

AtBPM1 belongs to the small family of Arabidopsis MATH and BTB domain proteins. A family of MATH-BTB proteins is known to act as substrate-specific adaptors of CUL3-based E3 ligases in the ubiquitin proteasome pathway. While BTB domain binds a CUL3 scaffold protein, the less conserved MATH domain targets a highly diverse collection of substrate proteins to promote their ubiquitination and subsequent degradation. Tandem affinity purification and yeast two hybrid assay revealed interaction of BPM1 with DMS3 and RDM1, crucial components of RNA-directed DNA methylation pathway (RdDM). Fluorescently tagged BPM1 and its truncated version with deletion of MATH or BTB domain showed that both domains are essential for accumulation of the protein in nucleolus, whilst co-localization results show significant overlap of BPM1 protein with aforementioned RdDM components. Yeast two hybrid assay using truncated BPM1 protein missing MATH or BTB domain revealed that the cullin3-binding BTB domain had higher affinity for RDM1 interaction while both, MATH and BTB domains proved to be equally important for DMS3 interaction. New insights into BPM1 protein and its interaction partners indicate an important, cullin independent function of MATH-BTB protein family in RdDM.

MATH-BTB, Arabidopsis thaliana, protein-protein interactions, RNA-directed DNA methylation

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