Condensate Formation by Structured dsRNA Binding Domains Drives RNA Sequestration in Plants

Area of Science:

• Molecular Biology
• Plant Science
• Virology

Background:

• Plants utilize dsRNA-binding proteins (DRBs) like DRB2, DRB3, and DRB5 for antiviral defense.
• These proteins sequester viral RNA within phase-separated viral replication complexes (VRCs).
• The precise molecular mechanisms of RNA sequestration and replication arrest by DRBs remain unclear.

Purpose of the Study:

• To elucidate the molecular mechanisms by which DRB2, DRB3, and DRB5 mediate viral RNA sequestration.
• To investigate the role of protein structure and phase separation in plant antiviral immunity.

Main Methods:

• Structural analysis of the dsRBD2 domain of DRB2/3/5.
• In vitro studies on dsRNA-binding and phase separation.
• Investigation of condensate formation triggers (dsRNA, molecular crowding, ATP).

Main Results:

• The dsRBD2 domain of DRB2/3/5 adopts a modified fold enabling dsRNA interaction and phase separation.
• Structural modifications create unique surface charge distributions promoting multivalent interactions.
• DRB2/3/5 proteins undergo concentration-dependent self-association and form gel-like condensates upon interaction with dsRNA or other triggers.

Conclusions:

• A mechanism for dsRNA-binding protein-induced phase separation is identified.
• RNA sequestration through condensate formation is proposed as a key contributor to plant antiviral immunity.