A plant-specific syntaxin-6 protein contributes to the intracytoplasmic route for the begomovirus CabLCV

Abstract

Due to limited free diffusion in the cytoplasm, viruses must use active transport mechanisms to move intracellularly. Nevertheless, how the plant ssDNA begomoviruses hijack the host intracytoplasmic transport machinery to move from the nucleus to the plasmodesmata remains enigmatic. Here, we identified nuclear shuttle protein (NSP)-interacting proteins from Arabidopsis (Arabidopsis thaliana) by probing a protein microarray and demonstrated that the cabbage leaf curl virus (CabLCV) NSP, a facilitator of the nucleocytoplasmic trafficking of viral (v)DNA, interacts in planta with an endosomal vesicle-localized, plant-specific syntaxin-6 protein, designated NSP-interacting syntaxin-6 domain-containing protein (NISP). NISP displays a pro-viral function, unlike the syntaxin-6 paralog AT2G18860 that failed to interact with NSP. Consistent with these findings, nisp-1 mutant plants were less susceptible to begomovirus infection, a phenotype reversed by NISP complementation. NISP-overexpressing lines accumulated higher levels of viral DNA than wild-type. Furthermore, NISP interacted with NIG, an NSP-interacting GTPase involved in NSP-vDNA nucleocytoplasmic translocation. The NISP-NIG interaction was enhanced by NSP. We also showed that endosomal NISP associates with vDNA. NISP may function as a docking site for recruiting NIG and NSP into endosomes, providing a mechanism for the intracytoplasmic translocation of the NSP-vDNA complex towards and from the cell periphery.

A sword or a buffet: plant endomembrane system in viral infections

“…NISP, which harbors a syntaxin-6 domain at the N-terminus and a transmembrane segment at the C-terminus, exhibits a proviral function as the nisp1 mutant is less susceptible to begomovirus infection. Using fluorescent molecular markers and FM4-64 labeling, NISP-GFP was localized to early endosomes ( Gouveia-Mageste et al., 2021 ). These findings suggest that NISP may function in recruitment of begomoviral NSPs to the early endosomal membrane where they may, among other functions, inhibit the NIK-containing PRR complexes.…”

Clustered Regularly Interspaced Short Palindromic Repeats-Associated Protein System for Resistance Against Plant Viruses: Applications and Perspectives

“…In fact, the inactivation of a necessary host factor for infection is supposed to account for recessively inherited disease resistance to plant viruses. For the ssDNA bipartite begomoviruses, two susceptibility genes, the endosomal NSP-interacting syntaxin-6 domain-containing protein (NISP), and NSP-interacting GTPase (NIG), which are involved in the intracellular traffic of viral DNA, may be targets for enhancing resistance in crops ( Carvalho et al, 2008 ; Gouveia-Mageste et al, 2021 ). Silencing of NISP enhanced resistance to cabbage leaf curl virus (CabLCV) in Arabidopsis without yield penalty, an essential property for considering susceptibility genes as targets for engineering recessive resistance.…”

“…Silencing of NISP enhanced resistance to cabbage leaf curl virus (CabLCV) in Arabidopsis without yield penalty, an essential property for considering susceptibility genes as targets for engineering recessive resistance. Accordingly, the silenced lines display lower DNA viral load and attenuated symptoms and are phenotypically indistinguishable from the control lines under normal conditions ( Gouveia-Mageste et al, 2021 ). Likewise, CRISPR/Cas9 sgRNA has been employed to target the susceptibility gene (S-gene) SIPelo for the monopartite begomovirus TYLCV inducing resistance in edited tomato plants against the virus ( Pramanik et al, 2021b ).…”

Begomovirus–Host Interactions: Viral Proteins Orchestrating Intra and Intercellular Transport of Viral DNA While Suppressing Host Defense Mechanisms

“…The intra- and intercellular transport functions of begomoviral shuttling and movement proteins make them valuable targets for the identification of host factors in fundamental cellular processes exploited by begomoviruses. These viral proteins interact with host factors in various organelles and are therefore potential hubs in the host–virus protein–protein interaction network [ 6 ].…”

“…Genome-wide studies focusing on plant immunity and pathogen infection strategies have provided an integrated picture of interactions between pathogens and plants [ 7 ]. This interaction network reveals that pathogen effectors and plant defense proteins converge, forming highly interconnected subsets of host proteins known as immune hubs [ 6 , 7 ]. Remarkably, these immune hubs conserve effectors from evolutionarily distinct pathogens, including the gram-negative bacterium Pseudomonas syringae (Psy) and the obligate biotrophic oomycete Hyaloperonospora arabidopsidis (Hpa) [ 7 ].…”