Glucose-6-phosphate dehydrogenase promotes the infection of Chilli veinal mottle virus through affecting ROS signaling in Nicotiana benthamiana

MiR827 positively regulates the resistance to chilli veinal mottle virus by affecting the expression of FBPase in Nicotiana benthamiana

MicroRNA(miRNA) is a class of non-coding small RNA that plays an important role in plant growth, development, and response to environmental stresses. Unlike most miRNAs, which usually target homologous genes across a variety of species, miR827 targets different types of genes in different species. Research on miR827 mainly focuses on its role in regulating phosphate (Pi) homeostasis of plants, however, little is known about its function in plant response to virus infection. In the present study, miR827 was significantly upregulated in the recovery tissue of virus-infected Nicotiana tabacum. Overexpression of miR827 could improve plants resistance to the infection of chilli veinal mottle virus (ChiVMV) in Nicotiana benthamiana, whereas interference of miR827 increased the susceptibility of the virus-infected plants. Further experiments indicated that the antiviral defence regulated by miR827 was associated with the reactive oxygen species and salicylic acid signalling pathways. Then, fructose-1,6-bisphosphatase (FBPase) was identified to be a target of miR827, and virus infection could affect the expression of FBPase. Finally, transient expression of FBPase increased the susceptibility to ChiVMV-GFP infection in N. benthamiana. By contrast, silencing of FBPase increased plant resistance. Taken together, our results demonstrate that miR827 plays a positive role in tobacco response to virus infection, thus providing new insights into understanding the role of miR827 in plant-virus interaction.

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.

Cucumber mosaic virus impairs the physiological homeostasis of Panax notoginseng and induces saponin-mediated resistance

As an important medicinal plant, Panax notoginseng often suffers from various abiotic and biotic stresses during its growth, such as drought, heavy metals, fungi, bacteria and viruses. In this study, the symptom and physiological parameters of cucumber mosaic virus (CMV)-infected P. notoginseng were analyzed and the RNA-seq was performed. The results showed that CMV infection affected the photosynthesis of P. notoginseng, caused serious oxidative damage to P. notoginseng and increased the activity of several antioxidant enzymes. Results of transcriptome analysis and corresponding verification showed that CMV infection changed the expression of genes related to plant defense and promoted the synthesis of P. notoginseng saponins to a certain extent, which may be defensive ways of P. notoginseng against CMV infection. Furthermore, pretreatment plants with saponins reduced the accumulation of CMV. Thus, our results provide new insights into the role of saponins in P. notoginseng response to virus infection.

miRNAs are involved in regulating the formation of recovery tissues in virus infected Nicotiana tabacum

MiRNAs play an important role in regulating plant growth and immune response. Mosaic diseases are recognized as the most important plant diseases in the world, and mosaic symptoms are recovery tissues formed by plants against virus infection. However, the mechanism of the formation of mosaic symptoms remains elusive. In this study, two typical mosaic systems consisting of Nicotiana tabacum-cucumber mosaic virus (CMV) and N. tabacum-tobacco mosaic virus (TMV) were used to investigate the relevance of miRNAs to the appearance of mosaic symptoms. The results of miRNA-seq showed that there were significant differences in miRNA abundance between dark green tissues and chlorotic tissues in mosaic leaves caused by the infection of CMV or TMV. Compared with healthy tissues, miRNA expression was significantly increased in chlorotic tissues, but slightly increased in dark green tissues. Three miRNAs, namely miR1919, miR390a, and miR6157, were identified to be strongly up-regulated in chlorotic tissues of both mosaic systems. Results of overexpressing or silencing of the three miRNAs proved that they were related to chlorophyll synthesis, auxin response, and small GTPase-mediated immunity pathway, which were corresponding to the phenotype, physiological parameters and susceptibility of the chlorotic tissues in mosaic leaves. Besides, the newly identified novel-miRNA48, novel-miRNA96 and novel-miRNA103 may also be involved in this formation of mosaic symptoms. Taken together, our results demonstrated that miR1919, miR390a and miR6157 are involved in the formation of mosaic symptoms and plant antiviral responses, providing new insight into the role of miRNAs in the formation of recovery tissue and plant immunity.

ATG8f Interacts with Chilli Veinal Mottle Virus 6K2 Protein to Limit Virus Infection

Autophagy, as a conserved protein degradation pathway in plants, has also been reported to be intricately associated with antiviral defense mechanisms. However, the relationship between chilli veinal mottle virus (ChiVMV) and autophagy has not been investigated in the existing research. Here, we reveal that ChiVMV infection caused the accumulation of autophagosomes in infected Nicotiana benthamiana leaves and the upregulation of autophagy-related genes (ATGs). Moreover, the changes in gene expression were correlated with the development of symptoms. Treatment with autophagy inhibitors (3-MA or E-64D) could increase the infection sites and facilitate virus infection, whereas treatment with the autophagy activator (Rapamycin) limited virus infection. Then, ATG8f was identified to interact with ChiVMV 6K2 protein directly in vitro and in vivo. The silencing of ATG8f promoted virus infection, whereas the overexpression of ATG8f inhibited virus infection. Furthermore, the expression of 6K2-GFP in ATG8f- or ATG7-silenced plants was significantly higher than that in control plants. Rapamycin treatment reduced the accumulation of 6K2-GFP in plant cells, whereas treatment with the inhibitor of the ubiquitin pathway (MG132), 3-MA, or E-64D displayed little impact on the accumulation of 6K2-GFP. Thus, our results demonstrated that ATG8f interacts with the ChiVMV 6K2 protein, promoting the degradation of 6K2 through the autophagy pathway.

Fuels for ROS signaling in plant immunity

Reactive oxygen species (ROS) signaling has an important role in plant innate immune responses and is primarily mediated by NADPH oxidase, also known as respiratory burst oxidase homologs (RBOHs) in plants. NADPH serves as a fuel for RBOHs and limits the rate or amount of ROS production. Molecular regulation of RBOHs has been extensively studied; however, the source of NADPH for RBOHs has received little attention. Here, we review ROS signaling and the regulation of RBOHs in the plant immune system with a focus on NADPH regulation to achieve ROS homeostasis. We propose an idea to regulate the levels of NADPH as part of a new strategy to control ROS signaling and the corresponding downstream defense responses.

Catalases mediate tobacco resistance to virus infection through crosstalk between salicylic acid and auxin signaling pathways

Catalases (CATs) play important roles in plant growth, development and defense responses. Previous studies have shown that CATs exhibit different or even opposite effects on plant immunity in different plant-pathogen interactions, but little is known about the mechanisms. In this study, Nicotiana tabacum plants with overexpression or knockout of CAT genes, tobacco mosaic virus (TMV) and cucumber mosaic virus (CMV) were employed to investigate the role of CAT in compatible plant-virus interactions. The results showed that there were dynamic changes in the effect of CAT on N. tabacum defense responses. Overexpression of catalase 1 (CAT1) and catalase 3 (CAT3) improved N. tabacum resistance in the early stage of virus infection but depressed it during the late stages of pathogenesis, especially in CAT3 overexpressing plants. The lower level of electrolyte leakage, lower contents of malonaldehyde and hydrogen peroxide (H2 O2 ), higher activities of antioxidant enzymes and improved functions of photosystem II corresponded to the milder symptoms and higher resistance of infected tobacco plants. In addition, the infection of TMV and CMV resulted in expression changes of CATs in tobacco plants, and pretreatment with H2 O2 facilitated TMV and CMV infection. Further experiments showed that the content of salicylic acid (SA) and the expression of genes related to SA signaling pathway were positively correlated with plant resistance, whereas auxin and its related signaling pathway were related to the viral susceptibility of plants. Taken together, our results demonstrated that CAT1 and CAT3 mediated tobacco resistance to virus infection through crosstalk between SA and auxin signaling pathways.

ZmG6PDH1 in glucose-6-phosphate dehydrogenase family enhances cold stress tolerance in maize

Glucose-6-phosphate dehydrogenase (G6PDH) is a key enzyme in the pentose phosphate pathway responsible for the generation of nicotinamide adenine dinucleotide phosphate (NADPH), thereby playing a central role in facilitating cellular responses to stress and maintaining redox homeostasis. This study aimed to characterize five G6PDH gene family members in maize. The classification of these ZmG6PDHs into plastidic and cytosolic isoforms was enabled by phylogenetic and transit peptide predictive analyses and confirmed by subcellular localization imaging analyses using maize mesophyll protoplasts. These ZmG6PDH genes exhibited distinctive expression patterns across tissues and developmental stages. Exposure to stressors, including cold, osmotic stress, salinity, and alkaline conditions, also significantly affected the expression and activity of the ZmG6PDHs, with particularly high expression of a cytosolic isoform (ZmG6PDH1) in response to cold stress and closely correlated with G6PDH enzymatic activity, suggesting that it may play a central role in shaping responses to cold conditions. CRISPR/Cas9-mediated knockout of ZmG6PDH1 on the B73 background led to enhanced cold stress sensitivity. Significant changes in the redox status of the NADPH, ascorbic acid (ASA), and glutathione (GSH) pools were observed after exposure of the zmg6pdh1 mutants to cold stress, with this disrupted redox balance contributing to increased production of reactive oxygen species and resultant cellular damage and death. Overall, these results highlight the importance of cytosolic ZmG6PDH1 in supporting maize resistance to cold stress, at least in part by producing NADPH that can be used by the ASA-GSH cycle to mitigate cold-induced oxidative damage.