From a Movement-Deficient Grapevine Fanleaf Virus to the Identification of a New Viral Determinant of Nematode Transmission

Nanobody-guided redox and enzymatic functionalization of icosahedral virus particles for enhanced bioelectrocatalysis

Icosahedral, 30 nm diameter, grapevine fanleaf virus (GFLV) virus particles are adsorbed onto electrodes and used as nanoscaffolds for the assembly of an integrated glucose oxidizing system, comprising the enzyme pyrroloquinoline quinone-glucose dehydrogenase (PQQ-GDH) and ferrocenylated polyethylene glycol chains (Fc-PEG) as a redox co-substrate. Two different GFLV-specific nanobodies, either fused to the enzyme, or chemically conjugated to Fc-PEG, are used for the regio-selective immunodecoration of the viral particles. A comprehensive kinetic characterization of the enzymatic function of the particles, initially decorated with the enzyme alone shows that simple immobilization on the GFLV capsid has no effect on the kinetic scheme of the enzyme, nor on its catalytic activity. However, we find that co-immobilization of the enzyme and the Fc-PEG co-substrate on GFLV does induce enzymatic enhancement, by promoting cooperativity between the two subunits of the homodimeric enzyme, via "synchronization" of their redox state. A decrease in inhibition of the enzyme by its substrate (glucose) is also observed.

Establishment of Arthrobotrys flagrans as biocontrol agent against the root pathogenic nematode Xiphinema index

Plant-parasitic nematodes cause devastating agricultural damage worldwide. Only a few synthetic nematicides can be used and their application is limited in fields. Therefore, there is a need for sustainable and environment-friendly alternatives. Nematode-trapping fungi (NTF) are natural predators of nematodes. They capture and digest them with their hyphae and are starting to being used as bio-control agents. In this study, we applied the NTF Arthrobotrys flagrans (Duddingtonia flagrans) against the wine pathogenic nematode Xiphinema index. A. flagrans reduced the number of X. index juveniles in pot cultures of Ficus carica, an alternative host plant for X. index, significantly. Sodium-alginate pellets with A. flagrans spores were produced for vineyard soil inoculation under laboratory conditions. The NTF A. conoides, A. musiformis and A. superba were enriched from several soil samples, showing their natural presence. Trap formation is an energy-consuming process and depends upon various biotic and abiotic stimuli. Here, we show that bacteria of the genus Delftia, Bacillus, Pseudomonas, Enterobacter and Serratia induced trap formation in NTF like A. conoides and A. oligospora but not in A. flagrans in the absence of nematodes. The application of NTF along with such bacteria could be a combinatorial way of efficient biocontrol in nematode-infested soil.

Small hydrophobic viral proteins involved in intercellular movement of diverse plant virus genomes

Most plant viruses code for movement proteins (MPs) targeting plasmodesmata to enable cell-to-cell and systemic spread in infected plants. Small membrane-embedded MPs have been first identified in two viral transport gene modules, triple gene block (TGB) coding for an RNA-binding helicase TGB1 and two small hydrophobic proteins TGB2 and TGB3 and double gene block (DGB) encoding two small polypeptides representing an RNA-binding protein and a membrane protein. These findings indicated that movement gene modules composed of two or more cistrons may encode the nucleic acid-binding protein and at least one membrane-bound movement protein. The same rule was revealed for small DNA-containing plant viruses, namely, viruses belonging to genus Mastrevirus (family Geminiviridae) and the family Nanoviridae. In multi-component transport modules the nucleic acid-binding MP can be viral capsid protein(s), as in RNA-containing viruses of the families Closteroviridae and Potyviridae. However, membrane proteins are always found among MPs of these multicomponent viral transport systems. Moreover, it was found that small membrane MPs encoded by many viruses can be involved in coupling viral replication and cell-to-cell movement. Currently, the studies of evolutionary origin and functioning of small membrane MPs is regarded as an important pre-requisite for understanding of the evolution of the existing plant virus transport systems. This paper represents the first comprehensive review which describes the whole diversity of small membrane MPs and presents the current views on their role in plant virus movement.