In vitro rearing of Perkinsiella saccharicida and the use of leaf segments to assay Fiji disease virus transmission

RNA N6 -methyladenosine modification suppresses replication of rice black streaked dwarf virus and is associated with virus persistence in its insect vector

N⁶ methylation of adenosine (m⁶ A) was recently discovered to play a role in regulating the life cycle of various viruses by modifying viral and host RNAs. However, different studies on m⁶ A effects on the same or different viruses have revealed contradictory roles for m⁶ A in the viral life cycle. In this study, we sought to define the role of m⁶ A on infection by rice black streaked dwarf virus (RBSDV), a double-stranded RNA virus, of its vector small brown planthopper (SBPH). Infection by RBSDV decreased the level of m⁶ A in midgut cells of SBPHs. We then cloned two genes (LsMETTL3 and LsMETTL14) that encode m⁶ A RNA methyltransferase in SBPHs. After interference with expression of the two genes, the titre of RBSDV in the midgut cells of SBPHs increased significantly, suggesting that m⁶ A levels were negatively correlated with virus replication. More importantly, our results revealed that m⁶ A modification might be the epigenetic mechanism that regulates RBSDV replication in its insect vector and maintains a certain virus threshold required for persistent transmission.

Insights Into Insect Vector Transmission and Epidemiology of Plant-Infecting Fijiviruses

Viruses in genus Fijivirus (family Reoviridae) have caused serious damage to rice, maize and sugarcane in American, Asian, European and Oceanian countries, where seven plant-infecting and two insect-specific viruses have been reported. Because the planthopper vectors are the only means of virus spread in nature, their migration and efficient transmission of these viruses among different crops or gramineous weeds in a persistent propagative manner are obligatory for virus epidemics. Understanding the mechanisms of virus transmission by these insect vectors is thus key for managing the spread of virus. This review describes current understandings of main fijiviruses and their insect vectors, transmission characteristics, effects of viruses on the behavior and physiology of vector insects, molecular transmission mechanisms. The relationships among transmission, virus epidemics and management are also discussed. To better understand fijivirus-plant disease system, research needs to focus on the complex interactions among the virus, insect vector, insect microbes, and plants.

Insect maintenance and transmission

Phytoplasmas are plant pathogens of huge economic importance due to responsibility for crop yield losses worldwide. Institutions around the world are trying to understand and control this yield loss at a time when food security is high on government agendas. In order to fully understand the mechanisms of phytoplasma infection and spread, more insect vector and phytoplasma colonies will need to be established for research worldwide. Rearing and study of these colonies is essential in the research and development of phytoplasma control measures. This chapter highlights general materials and methods for raising insect vector colonies and maintenance of phytoplasmas. Specific methods of rearing the maize leafhopper and maize bushy stunt phytoplasma and the aster leafhopper and aster yellows phytoplasma strain witches' broom are also included.

Identification of yeast associated with the planthopper, Perkinsiella saccharicida: potential applications for Fiji leaf gall control

Yeasts associate with numerous insects, and they can assist the metabolic processes within their hosts. Two distinct yeasts were identified by PCR within the planthopper Perkinsiella saccharicida, the vector of Fiji disease virus to sugarcane. The utility of both microbes for potential paratransgenic approaches to control Fiji leaf gall (FLG) was assessed. Phylogenetic analysis showed one of the microbes is related to yeast-like symbionts from the planthoppers: Laodelphax striatellus, Nilaparvata lugens, and Sogetella furcifera. The second yeast was a member of the Candida genus, a group that has been identified in beetles and recently described in planthoppers. Microscopy revealed the presence of yeast in the fat body of P. saccharicida. The Candida yeast was cultured, and transformation was accomplished by electroporation of Candida albicans codon optimized plasmids, designed to integrate into the genome via homologous recombination. Transgenic lines conferred resistance to the antibiotic nourseothricin and expression of green fluorescent protein was observed in a proportion of the yeast cells. Stably transformed yeast lines could not be isolated as the integrative plasmids presumably replicated within the yeast without integration into the genome. If stable transformation can be achieved, then this yeast may be useful as an agent for a paratransgenic control of FLG.