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MATH-BTB domain protein AtBPM1 directly interact with DMS3, important component of RNA-directed DNA methylation in plants

In Arabidopsis thaliana, the MATH-BTB (BPM) proteins comprise a small family of six members. BPMs act as substrate-binding adaptors for the Cullin3-based ubiquitin E3 ligase, and interect with a broad range of Ethylene response factor/apetala2 transcription factors and with homeodomain-leucine zipper transcription factor ATHB6 affecting fatty acid metabolism and abscisic acid signaling. We showed previously that AtBPM1, localizes predominantly in nucleolus of plant cells indicating a Cullin3 independent function. To further elucidate the molecular function of AtBPM1, we identified AtBPM1 binding and functional partners using tandem affinity purification and mass spectrometry. Different stress-related proteins were identified in AtBPM1 protein complexes such as Catalases CAT2 and CAT3, Nucleoside diphosphate kinase III, Glycine-rich RNA-binding proteins GRP7 and GRP8, MLP-like protein 423, Polyketide cyclase/dehydrase and lipid transport superfamily protein. Moreover, we have identified a set of DNA repair and chromatin remodeling proteins, such as Nucleosome assembly protein NAP1, Tudor-SN proteins, DNA-damage- repair/toleration protein DRT102, WD-40 repeat family protein/beige-related, Chromatin remodeling 34, DNA mismatch repair protein Msh6-1 as well as a known components of RNA-directed DNA methylation, defective in meristem silencing 3 DMS3 and RNA-directed DNA methylation 1 RDM1. Furthermore, direct interaction of AtBPM1 and DMS3 was confirmed by yeast two hybrid and pull down assays and DNA methylation in plants overexpressing AtBPM1 was reduced. These results, for the first time, links MATH-BTB proteins with DNA methylation and related mechanisms.

chromatin remodeling; protein-protein interactions; RNA-directed DNA methylation.

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