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.

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.

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

MAIN CONCLUSION: G6PDH negatively regulates viral accumulation in Nicotiana benthamiana through RBOHB-associated ROS signaling. Anti-oxidative metabolism and phytohormone-mediated immunity responses play important roles in virus infection. Glucose-6-phosphate dehydrogenase (G6PDH) is an enzyme in the pentose phosphate pathway, which plays an important role in maintaining intracellular redox homeostasis and has functions in plant growth, development and stress tolerance. However, the role of G6PDH in plants response to virus infection is poorly understood. In this study, NbG6PDH was found to be down-regulated after Chilli veinal mottle virus (ChiVMV-GFP) infection in Nicotiana benthamiana. Subcellular localization of NbG6PDH showed that it was punctate distributed in the protoplasm. Silencing of NbG6PDH reduced the sensitivity of N. benthamiana plants to ChiVMV-GFP. By contrast, transient overexpression of NbG6PDH promoted the accumulation of the virus. The results of physiological indexes showed that glutathione (GSH), catalase (CAT) and proline played an important role in maintaining plants physiological homeostasis. The results of gene expression detection showed that jasmonic acid/ethylene (JA/ET) signaling pathway was significantly correlated with the response of N. benthamiana to ChiVMV-GFP infection, and the changes of N. benthamiana respiratory burst oxidase homologues B (NbRBOHB) indicated that the NbG6PDH-dependent ROS may be regulated by NbRBOHB. Pretreatment of the inducer of reactive oxygen species (ROS) promoted virus infection, whereas inhibitor of ROS alleviated virus infection. Thus, our results indicate that the promoting effect of NbG6PDH on ChiVMV-GFP infection may be related to the NbRBOHB-regulated ROS production.

Construction of full-length cDNA infectious clones of Chilli veinal mottle virus.

Chilli veinal mottle virus (ChiVMV), a member of the genus Potyvirus in the family Potyviridae, causes severe diseases and poses a great threat to solanaceous crops. Reverse genetics technology is an efficient tool to facilitate the study of virus biology and pathogenicity. However, the construction of an infectious cDNA clone of ChiVMV is yet to be reported. In this study, full-length cDNA infectious clones of ChiVMV and GFP-tagged ChiVMV were constructed using yeast homologous recombination for the first time. These infectious clones were able to successfully infect host plants (Nicotiana benthamiana, Nicotiana tabacum and Solanum lycopersicum) by Agrobacterium-mediated infiltration and cause vein banding and leaf curling symptoms. Mutations were introduced to pChiVMV-GFP to investigate the role of key amino acids in ChiVMV 6K2. The results showed that substitution mutants of leucine (L9, 11) to alanine acid (A), tryptophan (W15) to alanine acid (A), and glycine (G29, 33) to valine acid (V) reduced the viral accumulation and the mutant clones were unable to induce the symptoms in N. benthamiana plants. Taken together, these infectious clones we developed will be effective tools for future studies of the function of viral factors encoded by ChiVMV and the interactions between ChiVMV and its different host plants.

Compound repair effect of carbon dots and Fe2+ on iron deficiency in Cucumis melon L.

Iron-deficiency is one of the most widespread micronutrient deficiency faced by plants, and proper iron supplementation is essential for the growth of crops and for people to obtain iron from food. In order to explore new methods of iron supplementation, we studied the repair effect of CDs on iron-deficient (Cucumis melo L.) muskmelon. Iron-deficient muskmelons were treated with different concentrations of Fe2+, CDs and their complexes. The results showed that CDs significantly increased the iron transport rate and it is noteworthy that 75 mg/L CDs increased the iron transport rate of 0.7 mg/L Fe2+ by 134%. The compound treatment reduced the oxidative stress caused by iron deficiency, such as the CAT activity in the leaves of the compound treatment group was 10%-50% lower than that of the iron supplementation alone. Fluorescent imaging results of melon proved that CDs entered into the muskmelon seedlings. In combination with the above results and the adsorption of CDs, we speculated that the way CDs promoted iron absorption and transport was most likely to combine with Fe2+ and co-transport in melon, which changed the content of reactive oxygen species and other free radicals, thus causing changes of physiological state of melon. This study confirmed that CDs had a positive effect on the iron deficiency of muskmelon, and improved the growth of muskmelon under the condition of iron deficiency, which has a certain reference value for further optimization of iron supplementation solution.