A nuclear import pathway exploited by pathogenic noncoding RNAs

Area of Science:

• Molecular Biology
• Plant Pathology
• Cell Biology

Background:

• Intracellular RNA trafficking typically involves nuclear export for function.
• Emerging evidence shows functional RNAs can move from cytoplasm to nucleus, but mechanisms are unclear.
• Viroids are plant-infecting circular noncoding RNAs.

Purpose of the Study:

• To elucidate the mechanism of RNA nuclear import.
• To investigate the role of cellular factors and RNA structures in viroid nuclear import.

Main Methods:

• Utilized Nicotiana benthamiana and tomato (Solanum lycopersicum) as model systems.
• Employed nuclear-replicating viroids to study RNA import pathways.
• Investigated the involvement of IMPORTIN ALPHA-4 (IMPa-4) and viroid RNA-binding protein 1 (VIRP1).

Main Results:

• Identified IMPORTIN ALPHA-4 (IMPa-4) as a key factor in viroid nuclear import.
• Confirmed the role of viroid RNA-binding protein 1 (VIRP1) in binding both IMPa-4 and viroid RNA.
• Demonstrated that a conserved C-loop in viroid RNA acts as a nuclear import signal, essential for VIRP1 binding, nuclear accumulation, and infectivity.
• Found the C-loop motif in a satellite noncoding RNA dependent on VIRP1 for nuclear import.

Conclusions:

• Viroid nuclear import involves the Importin-based cellular pathway, specifically IMPa-4.
• The C-loop is a critical RNA signal for nuclear import, mediated by VIRP1.
• These findings enhance understanding of subviral RNA infection and RNA nuclear import regulation.