Pepper mild mottle virus coat protein interacts with pepper chloroplast outer envelope membrane protein OMP24 to inhibit antiviral immunity in plants

Unveiling the Role of SlRNC1 in Chloroplast Development and Global Gene Regulation in Tomato Plants

RNC1, a plant-specific gene, is known for its involvement in splicing group II introns within maize chloroplast. However, its role in chloroplast development and global gene expression remains poorly understood. This study aimed to investigate the role of RNC1 in chloroplast development and identify the genes that mediate its function in the development of entire tomato plants. Consistent with findings in maize, RNC1 silencing induced dwarfism and leaf whitening in tomato plants. Subcellular localization analysis revealed that the RNC1 protein is localized to both the nucleus and cytoplasm, including the stress granule and chloroplasts. Electron microscopic examination of tomato leaf transverse sections exposed significant disruptions in the spatial arrangement of the thylakoid network upon RNC1 silencing, crucial for efficient light energy capture and conversion into chemical energy. Transcriptome analysis suggested that RNC1 silencing potentially impacts tomato plant development through genes associated with all three categories (biological processes, cellular components, and molecular functions). Overall, our findings contribute to a better understanding of the critical role of RNC1 in chloroplast development and its significance in plant physiology.

Adoption of the 2A Ribosomal Skip Principle to Track Assembled Virions of Pepper Mild Mottle Virus in Nicotiana benthamiana

The coat protein (CP) is an important structural protein that plays many functional roles during the viral cycle. In this study, the CP of pepper mild mottle virus (PMMoV) was genetically fused to GFP using the foot-and-mouth disease virus peptide 2A linker peptide and the construct (PMMoV-GFP2A) was shown to be infectious. The systemic spread of the virus was monitored by its fluorescence in infected plants. Electron microscopy and immunocolloidal gold labelling confirmed that PMMoV-GFP2A forms rod-shaped particles on which GFP is displayed. Studies of tissue ultrastructure and virion self-assembly confirmed that PMMoV-GFP2A could be used to monitor the real-time dynamic changes of CP location during virus infection. Aggregations of GFP-tagged virions appeared as fluorescent plaques in confocal laser microscopy. Altogether, PMMoV-GFP2A is a useful tool for studying the spatial and temporal changes of PMMoV CP during viral infection.

Plant virology in the 21st century in China: Recent advances and future directions

Plant viruses are a group of intracellular pathogens that persistently threaten global food security. Significant advances in plant virology have been achieved by Chinese scientists over the last 20 years, including basic research and technologies for preventing and controlling plant viral diseases. Here, we review these milestones and advances, including the identification of new crop-infecting viruses, dissection of pathogenic mechanisms of multiple viruses, examination of multilayered interactions among viruses, their host plants, and virus-transmitting arthropod vectors, and in-depth interrogation of plant-encoded resistance and susceptibility determinants. Notably, various plant virus-based vectors have also been successfully developed for gene function studies and target gene expression in plants. We also recommend future plant virology studies in China.

Rubisco small subunit (RbCS) is co-opted by potyvirids as the scaffold protein in assembling a complex for viral intercellular movement

Plant viruses must move through plasmodesmata (PD) to complete their life cycles. For viruses in the Potyviridae family (potyvirids), three viral factors (P3N-PIPO, CI, and CP) and few host proteins are known to participate in this event. Nevertheless, not all the proteins engaging in the cell-to-cell movement of potyvirids have been discovered. Here, we found that HCPro2 encoded by areca palm necrotic ring spot virus (ANRSV) assists viral intercellular movement, which could be functionally complemented by its counterpart HCPro from a potyvirus. Affinity purification and mass spectrometry identified several viral factors (including CI and CP) and host proteins that are physically associated with HCPro2. We demonstrated that HCPro2 interacts with both CI and CP in planta in forming PD-localized complexes during viral infection. Further, we screened HCPro2-associating host proteins, and identified a common host protein in Nicotiana benthamiana-Rubisco small subunit (NbRbCS) that mediates the interactions of HCPro2 with CI or CP, and CI with CP. Knockdown of NbRbCS impairs these interactions, and significantly attenuates the intercellular and systemic movement of ANRSV and three other potyvirids (turnip mosaic virus, pepper veinal mottle virus, and telosma mosaic virus). This study indicates that a nucleus-encoded chloroplast-targeted protein is hijacked by potyvirids as the scaffold protein to assemble a complex to facilitate viral movement across cells.

Chloroplast clustering around the nucleus induced by OMP24 overexpression unexpectedly promoted PSTVd infection in Nicotiana benthamiana

Chloroplast clustering around the nucleus is a well-known mechanism that occurs in response to various biotic and abiotic stresses and is believed to be a mechanism of defence against pathogens in plants. This phenomenon is accompanied by increased production of reactive oxygen species (ROS), which can help to destroy invading pathogens. However, the function of chloroplast clustering during viroid infection is unclear. Here, we report that, although the infection by potato spindle tuber viroid (PSTVd) failed to induce chloroplast clustering, chloroplast clustering caused by the overexpression of the Nicotiana benthamiana chloroplast outer membrane protein 24 (NbOMP24) promoted the infection by PSTVd, a viroid pathogen, in N. benthamiana. Interestingly, H2 O2 treatment, which caused increased ROS accumulation, showed no significant effects on PSTVd infection. Moreover, NbOMP24 protein showed no direct interaction with PSTVd. We propose that perinuclear chloroplast clustering induced by NbOMP24 provides a favourable environment for PSTVd infection. These findings highlight the complexity of chloroplast clustering-mediated plant-pathogen interactions and the need for further research to fully understand these mechanisms.