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Infection of novel cryptic virus observed in Pigeonpea plant

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Photo : Purabi Deshpande / Research Matters

Researchers from the CSIR- Institute of Himalayan Bioresource Technology, Palampur, Himachal Pradesh have discovered the presence of a novel cryptic virus tentatively called the Arhar cryptic virus-1 in Pigeonpea plants from pigeonpea field in Telangana state.

It is unclear in biology whether viruses can be considered as living beings. Viruses are a complex assembly of molecules consisting of an outer protein envelope within which the genetic material is housed. These complex materials can only replicate inside the body of a host, using the molecular machinery of the host to aid their replication. As the study of virology evolved, cryptic viruses were discovered.

Cryptic viruses evaded detection by scientists as they cause little or no symptoms in the infected plant. They contain double stranded RNA as genetic material and are not transmitted from infected to healthy cells as other viruses usually do. Plant crypto viruses are usually transmitted through pollen or seeds.

In their recent study, scientists reported for the first time an infection of the pigeonpea plant by a cryptic virus. Tentatively named Arhar cryptic virus-1, this discovery is important as pigeonpea is one of the major grain legume crops of the Indian subcontinent.

Four double stranded stand RNA segments were isolated from pigeonpea plants. Using a method called Sequence Independent Single Primer Amplification, the different genomic segments of the double stranded RNAs were characterized. Three out of the four isolated RNA formed the genome of the newly identified cryptic virus, while the fourth RNA resembled the protein coat of an unrelated virus.

Along with the characterisation of the entire genomic sequence of the cryptic virus, the researchers conducted a structural analysis of the RNA dependent RNA polymerase, an important enzyme required in the replication of the virus. Through the structural analysis of the enzyme and comparing it with other RNA dependent RNA polymerases the team were able to display that the sequence for this enzyme was conserved in cryptic viruses and which part of the sequence performed what function in replication.

From the information gathered through this study, the researchers hope that future biochemical and X-ray crystallography experiments will help us better understand RNA dependent RNA polymerases and their relevance in RNA synthesis.