''Idaeovirus'' is a genus of positive-sense ssRNA viruses that contains two species: ''Raspberry bushy dwarf virus'' (RBDV) and ''Privet idaeovirus''. RBDV has two host-dependent

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

s: one for raspberries; the other for

grapevines ''Vitis'' (grapevine) is a genus of 81 accepted species of vining plants in the flowering plant family Vitaceae. The genus consists of species predominantly from the Northern Hemisphere. It is economically important as the source of grapes, bot ...

. Infections are a significant agricultural burden, resulting in decreased yield and quality of crops. RBDV has a synergistic relation with '' Raspberry leaf mottle virus'', with co-infection greatly amplifying the concentration of virions in infected plants. The virus is transmitted via

pollination Pollination is the transfer of pollen from an anther of a plant to the stigma (botany), stigma of a plant, later enabling fertilisation and the production of seeds. Pollinating agents can be animals such as insects, for example bees, beetles or bu ...

with RBDV-infected pollen grains that first infect the stigma before causing systemic infection.

Virology

RBDV is non-enveloped with an isometric protein coat about 33 nanometres in diameter. Inside the protein coat is the viral genome, which is bipartite, with the

RNA Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...

strands referred to as RNA-1 and RNA-2. RNA-1 is 5,449

nucleotide Nucleotides are Organic compound, organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both o ...

s in length and contains one

open reading frame In molecular biology, reading frames are defined as spans of DNA sequence between the start and stop codons. Usually, this is considered within a studied region of a prokaryotic DNA sequence, where only one of the six possible reading frames ...

(ORF) that encodes for a combined protein that has methyltransferase,

helicase Helicases are a class of enzymes that are vital to all organisms. Their main function is to unpack an organism's genetic material. Helicases are motor proteins that move directionally along a nucleic double helix, separating the two hybridized ...

, and an

RNA-dependent RNA polymerase RNA-dependent RNA polymerase (RdRp) or RNA replicase is an enzyme that catalyzes the self-replication, replication of RNA from an RNA template. Specifically, it catalyzes synthesis of the RNA strand Complementarity (molecular biology), compleme ...

domains. RNA-2 is 2,231 nucleotides in length and contains two ORFs, one at the 5' end and the other at the 3' end. The first ORF encodes for a cell-to-cell movement protein, while the second ORF is expressed as a subgenomic RNA strand. This strand, RNA-3, is 946 nucleotides in length and encodes for the coat protein. Infection has been shown to not occur if RNA-3 is either not present or is sufficiently damaged.

Life cycle

Viral replication is cytoplasmic. Entry into the host cell is achieved by penetration into the host cell. Replication follows the positive stranded RNA virus replication model. Positive stranded RNA virus transcription is the method of transcription. The virus exits the host cell by tubule-guided viral movement. Plants serve as the natural host. Transmission routes are pollen associated.

Diagnosis

Single-step

reverse transcription polymerase chain reaction Reverse transcription polymerase chain reaction (RT-PCR) is a laboratory technique combining reverse transcription of RNA into DNA (in this context called complementary DNA or cDNA) and amplification of specific DNA targets using polymerase cha ...

s has been developed to detect RBDV. Viruses are enriched by antibodies in the PCR microwells, followed by

lysis Lysis ( ; from Greek 'loosening') is the breaking down of the membrane of a cell, often by viral, enzymic, or osmotic (that is, "lytic" ) mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a ...

of the virus particles, then reverse transcription of the viral RNA. By including

reverse transcriptase A reverse transcriptase (RT) is an enzyme used to convert RNA genome to DNA, a process termed reverse transcription. Reverse transcriptases are used by viruses such as HIV and hepatitis B to replicate their genomes, by retrotransposon mobi ...

and

DNA polymerase A DNA polymerase is a member of a family of enzymes that catalyze the synthesis of DNA molecules from nucleoside triphosphates, the molecular precursors of DNA. These enzymes are essential for DNA replication and usually work in groups to create t ...

in the whole process, the procedure can be conducted in a single step. These tests are sensitive enough to identify the specific strain of the virus.

Treatment

RBDV can be eradicated from infected plants by a procedure that first applies

thermotherapy Heat therapy, also called thermotherapy, is the use of heat in therapy, such as for pain relief and health. It can take the form of a hot cloth, hot water bottle, ultrasound, heating pad, hydrocollator packs, whirlpool baths, cordless Far infra ...

then

cryotherapy Cryotherapy, sometimes known as cold therapy, is the local or general use of low temperatures in medical therapy. Cryotherapy can be used in many ways, including whole body exposure for therapeutic health benefits or may be used locally to treat ...

to infected shoots. Applying heat to infected plants causes

vacuole A vacuole () is a membrane-bound organelle which is present in Plant cell, plant and Fungus, fungal Cell (biology), cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water ...

s in infected cells to enlarge, with these cells later being killed during cryotherapy. Adding either Fe-

ethylenediaminetetraacetic acid Ethylenediaminetetraacetic acid (EDTA), also called EDTA acid, is an aminopolycarboxylic acid with the formula . This white, slightly water-soluble solid is widely used to bind to iron (Fe2+/Fe3+) and calcium ions (Ca2+), forming water-solubl ...

or Fe-ethylenediaminedi(o)hydroxyphenylacetic acid after cryotherapy stimulates regrowth and prevents

chlorosis In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to ...

from developing in plant shoots. Using this method, about 80% of shoots survive the initial heat therapy, with 33% surviving the cryotherapy and successfully regrowing.

References

External links

Viralzone: Idaeovirus

ICTV
{{Taxonbar, from=Q5987260 Positive-sense single-stranded RNA viruses Riboviria Virus genera