Reticulon-like properties of a plant virus-encoded movement protein

Area of Science:

• Plant virology
• Cell biology
• Membrane biophysics

Background:

• Plant viruses utilize movement proteins (MPs) to transport viral genomes through plasmodesmata (PD).
• Endoplasmic reticulum (ER) membranes are crucial for delivering viral genomes to PD and forming replication compartments.
• Reticulons are cellular proteins known to induce membrane curvature and shape ER tubules.

Purpose of the Study:

• To investigate the function of Hibiscus green spot virus (HGSV) movement protein BMB2 in ER and PD modification.
• To determine if BMB2's properties resemble cellular reticulons.
• To elucidate the mechanism by which BMB2 facilitates virus intercellular spread.

Main Methods:

• Analysis of BMB2's interaction with ER tubules and membrane curvature.
• Assessment of BMB2's effect on ER luminal content mobility.
• Investigation of BMB2's targeting to PD and its impact on PD size exclusion limit.
• Comparative analysis with Potato virus X (PVX) MP TGB2.

Main Results:

• HGSV BMB2 MP, an integral ER protein, induces ER tubule constrictions and exhibits affinity for curved membranes, similar to reticulons.
• BMB2 increases PD size exclusion limit, and this activity correlates with its ability to induce ER tubule constrictions.
• ER tubule constrictions are also observed with PVX TGB2 MP, suggesting a conserved mechanism among diverse RNA viruses.

Conclusions:

• BMB2-induced ER tubule constrictions contribute to increased PD permeability, facilitating virus intercellular spread.
• The reticulon-like activity of MPs in shaping ER tubules appears to be a conserved strategy employed by various plant viruses.
• This study reveals a novel role for ER membrane shaping in virus-cell to cell movement.