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Viral replication and movement are intimately linked; however, the molecular mechanisms regulating the transition between replication and subsequent movement remain largely unknown. We previously demonstrated that the Barley stripe mosaic virus (BSMV) γb protein promotes viral replication and movement by interacting with the αa replicase and TGB1 movement proteins. Here, we found that γb is palmitoylated at Cys‐10, Cys‐19, and Cys‐60 in Nicotiana benthamiana, which supports BSMV infection. Intriguingly, non‐palmitoylated γb is anchored to chloroplast replication sites and enhances BSMV replication, whereas palmitoylated γb protein recruits TGB1 to the chloroplasts and forms viral replication‐movement intermediate complexes. At the late stages of replication, γb interacts with NbPAT15 and NbPAT21 and is palmitoylated at the chloroplast periphery, thereby shifting viral replication to intracellular and intercellular movement. We also show that palmitoylated γb promotes virus cell‐to‐cell movement by interacting with NbREM1 to inhibit callose deposition at the plasmodesmata. Altogether, our experiments reveal a model whereby palmitoylation of γb directs a dynamic switch between BSMV replication and movement events during infection. Synopsis: Viral replication and subsequent intercellular movement are two critical steps for efficient plant infection. This work reveals induction of a replication‐to‐movement switch by palmitoylation of the viral γb protein during Barley stripe mosaic virus (BSMV) infection. Non‐palmitoylated γb is anchored to the chloroplasts and promotes BSMV replication.During the late stages of replication, S‐acyltransferases NbPAT15 and NbPAT21 palmitoylate γb at the periphery of chloroplasts.Palmitoylated γb recruits the TGB1 movement protein to chloroplasts, thereby inducing a shift between viral replication and movement phases.Palmitoylated γb promotes viral cell‐to‐cell movement by inhibiting NbREM1‐dependent callose deposition at plasmodesmata. [ABSTRACT FROM AUTHOR]

The plant antioxidant system plays important roles in response to diverse abiotic and biotic stresses. However, the effects of virus infection on host redox homeostasis and how antioxidant defense pathway is manipulated by viruses remain poorly understood. We previously demonstrated that the Barley stripe mosaic virus (BSMV) γb protein is recruited to the chloroplast by the viral αa replicase to enhance viral replication. Here, we show that BSMV infection induces chloroplast oxidative stress. The versatile γb protein interacts directly with NADPH‐dependent thioredoxin reductase C (NTRC), a core component of chloroplast antioxidant systems. Overexpression of NbNTRC significantly impairs BSMV replication in Nicotiana benthamiana plants, whereas disruption of NbNTRC expression leads to increased viral accumulation and infection severity. To counter NTRC‐mediated defenses, BSMV employs the γb protein to competitively interfere with NbNTRC binding to 2‐Cys Prx. Altogether, this study indicates that beyond acting as a helicase enhancer, γb also subverts NTRC‐mediated chloroplast antioxidant defenses to create an oxidative microenvironment conducive to viral replication. SYNOPSIS: The Barley stripe mosaic virus (BSMV) γb protein promotes viral infection in plants via various mechanisms. This work reveals an additional role in disrupting chloroplast antioxidant defenses to create an oxidative microenvironment conducive to viral replication. BSMV infection disturbs chloroplast redox homeostasis and induces oxidative stress.The BSMV γb protein directly interacts with host NADPH‐dependent thioredoxin reductase C (NTRC) at chloroplasts.NTRC expression suppresses BSMV replication in Nicotiana benthamiana.γb protein competitively interferes with NTRC binding to 2‐Cys peroxiredoxins. [ABSTRACT FROM AUTHOR]

Selective autophagy mediates specific degradation of unwanted cytoplasmic components to maintain cellular homeostasis. The suppressor of gene silencing 3 (SGS3) and RNA‐dependent RNA polymerase 6 (RDR6)‐formed bodies (SGS3/RDR6 bodies) are essential for siRNA amplification in planta. However, whether autophagy receptors regulate selective turnover of SGS3/RDR6 bodies is unknown. By analyzing the transcriptomic response to virus infection in Arabidopsis, we identified a virus‐induced small peptide 1 (VISP1) composed of 71 amino acids, which harbor a ubiquitin‐interacting motif that mediates interaction with autophagy‐related protein 8. Overexpression of VISP1 induced selective autophagy and compromised antiviral immunity by inhibiting SGS3/RDR6‐dependent viral siRNA amplification, whereas visp1 mutants exhibited opposite effects. Biochemistry assays demonstrate that VISP1 interacted with SGS3 and mediated autophagic degradation of SGS3/RDR6 bodies. Further analyses revealed that overexpression of VISP1, mimicking the sgs3 mutant, impaired biogenesis of endogenous trans‐acting siRNAs and up‐regulated their targets. Collectively, we propose that VISP1 is a small peptide receptor functioning in the crosstalk between selective autophagy and RNA silencing. Synopsis: Genomic analyses have predicted numerous potentially expressed small peptides in plants, but their functions remain largely unknown. Here, a virus‐induced peptide is identified as a new autophagy receptor triggering degradation of SGS3/RDR6‐bodies and negatively regulating siRNA amplification. VISP1 is a novel virus‐induced small peptide composed of 71 amino acids in Arabidopsis.VISP1 harbors a ubiquitin‐interacting motif (UIM), which mediates the interaction with ATG8.VISP1 serves as a new autophagy receptor and triggers autophagic degradation of SGS3/RDR6‐bodies.VISP1 negatively regulates SGS3/RDR6‐dependent siRNA amplification. [ABSTRACT FROM AUTHOR]