Advances in understanding multifunctionality of Barley stripe mosaic virus γb protein

Abstract

Plant viruses usually encode versatile but limited number of proteins to reshape the cellular microenvironment, suppress or co-opt host pathways and proteins for their own benefit. Barley stripe mosaic virus (BSMV, Hordeivirus hordei) is a positive single-stranded RNA virus that infects both monocots and dicots. Among its seven encoded proteins, the γb protein exhibits remarkable multifunctionality despite being the smallest one. By interacting with various viral and host proteins, γb acts as a master regulator participating in almost all steps of the viral life cycle, including replication, movement, virion morphogenesis and vertical transmission, in addition to counteracting several layers of host defenses. In this review, we systematically summarize current understanding of the γb protein multifunctionality and discuss its implications in the ongoing co-evolutionary battle between host plants and invading viruses.

Fig 1. Symptoms and genome organization of Barley stripe mosaic virus (BSMV).

(A) The uniform distribution of γb on BSMV particles, as visualized using the immunogold labeling approach. This panel is adapted with permission from [32]. (B) Representative symptoms induced by BSMV on different monocot and dicot plants. (C) The BSMV genome consists of three RNAs, designated RNAα, RNAβ, and RNAγ. Each RNA features a 5′ cap structure (m7G) and a 3′ internal polyadenylate sequence.

Fig 2. Characterization of the γb protein.

(A) The key amino acids and motifs contributing to the multifunctionality of the γb protein. (B) Amino acid sequence alignment of CRP proteins in different genera of Virgaviridae. The conserved CCCH motif (Cys-50, Cys-60, Cys-81 and His-85 for BSMV strain ND18) are highlighted in dark grey. (C) A schematic diagram illustrating the interactions between different regions of the γb protein and various proteins.

Fig 3. A timeline summarizing progress in understanding the multifunctionality of the BSMV γb protein.

Fig 4. A simplified model to show the involvement of γb at different stages of BSMV infection.

Fig 5. γb manipulates host defense responses.

During BSMV infection, the γb protein targets to various proteins to disturb host antiviral defense, such as SA signaling pathway, RNA silencing, autophagy, ROS burst, and cell death, which, in turn, facilitating virus infection. TRXh: thioredoxin h-type; RH20: DEAD-box RNA helicase 20; SGS3: Suppressor of Gene Silencing 3; RDR6: RNA-Dependent RNA Polymerase 6; Per: Peroxisome; GOX: Glycolate oxidase; PKA: Protein kinase A; NTRC: NADPH-dependent thioredoxin reductase C. Created with BioRender.com.