Physical contact transmission of Cucumber green mottle mosaic virus by Myzus persicae

Evolution of cucurbit-infecting tobamoviruses: Recombination and codon usage bias

Currently, there are seven cucurbit-infecting tobamoviruses comprising cucumber green mottle mosaic virus (CGMMV), Kyuri green mottle mosaic virus (KGMMV), cucumber fruit mottle mosaic virus (CFMMV), zucchini green mottle mosaic virus (ZGMMV), cucumber mottle virus (CMoV), watermelon green mottle mosaic virus (WGMMV), and Trichosanthes mottle mosaic virus (TrMMV). To gain more insights into their evolution, recombination analyses were conducted. Four CGMMV isolates and one KGMMV isolate were suggested to be recombinants. And there was an interspecies recombination event between CGMMV and ZGMMV. Phylogenetic incongruence was also observed for CGMMV and KGMMV. A probable ancestral pattern was inferred for the gene junction region between RdRp and MP. Codon usage bias analysis revealed that the viral genes had additional influence independent of compositional constraint. In codon preference, the seven viruses were both similar to and different from the host cucumber (Cucumis sativus). Moreover, the viruses were not deficient in CpG and UpA dinucleotides.

Reactive oxygen species-related genes participate in resistance to cucumber green mottle mosaic virus infection regulated by boron in Nicotiana benthamiana and watermelon

Cucumber green mottle mosaic virus (CGMMV) infection causes acidification and rot of watermelon flesh, resulting in serious economic losses. It is widely reported the interaction relationship between boron and reactive oxygen species (ROS) in regulating normal growth and disease resistance in plants. Our previous results demonstrated that exogenous boron could improve watermelon resistance to CGMMV infection. However, the roles of ROS-related genes regulated by boron in resistance to CGMMV infection are unclear. Here, we demonstrated that CGMMV symptoms were alleviated, and viral accumulations were decreased by boron application in Nicotiana benthamiana, indicating that boron contributed to inhibiting CGMMV infection. Meanwhile, we found that a number of differentially expressed genes (DEGs) associated with inositol biosynthesis, ethylene synthesis, Ca²⁺ signaling transduction and ROS scavenging system were up-regulated, while many DEGs involved in ABA catabolism, GA signal transduction and ascorbic acid metabolism were down-regulated by boron application under CGMMV infection. Additionally, we individually silenced nine ROS-related genes to explore their anti-CGMMV roles using a tobacco rattle virus (TRV) vector. The results showed that NbCat1, NbGME1, NbGGP and NbPrx Q were required for CGMMV infection, while NbGST and NbIPS played roles in resistance to CGMMV infection. The similar results were obtained in watermelon by silencing of ClCat, ClPrx or ClGST expression using a pV190 vector. This study proposed a new strategy for improving plant resistance to CGMMV infection by boron-regulated ROS pathway and provided several target genes for watermelon disease resistance breeding.