Table of Contents
Genus Botybirnavirus: A Deep Dive into Bipartite dsRNA Mycoviruses
Last Updated: July 29, 2025
Author Bio: This research summary is based on the doctoral thesis of Wajeeha Shamsi, a researcher from the Atta-ur-Rahman School of Applied Biosciences at the National University of Sciences & Technology (NUST), Islamabad. Her work focuses on the identification and characterization of novel mycoviruses from environmental sources.
Introduction
As scientists discover thousands of new viruses, organizing them into a coherent system is one of the greatest challenges in modern virology. This classification, or taxonomy, helps us understand their evolutionary history, predict their behavior, and identify their unique characteristics.
In the world of fungal viruses, new classifications are constantly emerging. A particularly interesting and recently recognized group is the genus Botybirnavirus. This distinct group of mycoviruses has a unique genomic structure that sets it apart. Drawing from the comprehensive literature review and novel findings in Wajeeha Shamsi’s 2020 thesis, we will explore the defining features of this fascinating genus.
The Prototype: The Discovery of a New Viral Lineage
The story of the genus Botybirnavirus begins with the discovery of a novel bipartite dsRNA virus identified from a hypovirulent strain of the fungus Botrytis porri. Originally named Botrytis porri RNA virus 1 (BpRV1), its genetic and structural properties were so unique that they didn’t fit neatly into any existing mycovirus family.
Phylogenetic analysis revealed that BpRV1 formed a distinct clade away from other known mycoviruses. It exhibited a number of features that differentiated it from other reported viruses, leading researchers to propose placing it in a new family, ‘Botybirnaviridae’. The ‘Boty’ in the name originates from its host ‘Botrytis’ while ‘-birna’ is representative of the bipartite (two-part) nature of its genome. The International Committee on Taxonomy of Viruses (ICTV) later recognized the new genus Botybirnavirus, with BpBRV1 as its prototype member.
Defining Characteristics of the Genus Botybirnavirus
All members of the genus Botybirnavirus identified so far share a set of specific characteristics that define their classification. These features create a clear biological and molecular signature for this group:
- A Bipartite dsRNA Genome: Their genetic material consists of two separate double-stranded RNA segments, typically ranging in size from 5.4 to 6.5 kilobase pairs (kbp).
- High Conservation at the 5′ UTRs: The viruses show high levels of conservation in their 5′ untranslated regions (UTRs), suggesting these areas play a critical role in the viral life cycle.
- A Single Open Reading Frame (ORF): Each of the two RNA segments contains a single, large gene or ORF.
- Spherical Virions: The virus particles are isometric (roughly spherical) and typically measure 35-40 nanometers in diameter.
- Stable Stem-Loop Structures: The terminal ends of their genomes form stable stem-loop secondary structures, which are believed to provide stability and aid in replication.
A New Member: Alternaria alternata botybirnavirus 1 (AaBbV1)
The research detailed in the thesis led to the discovery of a novel virus, Alternaria alternata botybirnavirus 1 (AaBbV1), which was found to possess all the hallmark attributes of the genus Botybirnavirus. Its characterization confirmed it as a new species within this classification.
AaBbV1 showed sequence similarities to previously reported botybirnaviruses, particularly the prototype BpBRV1. These observations, combined with its phylogenetic relationship, confirmed AaBbV1 as a member of this new species. To date, around ten other botybirnaviruses have been identified, expanding our understanding of this unique viral group.
The Role of Botybirnaviruses in Hypovirulence
Several members of the genus Botybirnavirus are known to confer hypovirulence in their fungal hosts, reducing their ability to cause disease. These include:
- BpBRV1: The prototype member, which causes hypovirulence in Botrytis porri.
- Sclerotinia sclerotiorum botybirnavirus 1 (SsBRV1): Confers hypovirulence in the presence of a satellite RNA.
- Sclerotinia sclerotiorum botybirnavirus 2 (SsBRV2)
- Botryosphaeria dothidea botybirnavirus 1 (BdBRV1)
Interestingly, the newly discovered AaBbV1 appeared to be asymptomatic in its host, causing no obvious signs of disease. This highlights the complexity of virus-host interactions; symptom induction can depend heavily on the specific virus-host combination, and a lack of symptoms under one condition does not mean the virus is entirely inert. It may manifest symptoms under different environmental conditions, making the term “cryptic” more appropriate.
Conclusion
The genus Botyvirnavirus represents a distinct and growing lineage of bipartite dsRNA mycoviruses. Characterized by their unique two-part genome, spherical shape, and conserved genetic features, they provide a fascinating case study in viral evolution and classification. The discovery and detailed characterization of new members like Alternaria alternata botybirnavirus 1 are essential for refining our taxonomic framework and deepening our understanding of the complex roles these viruses play within their fungal hosts, from cryptic infections to potent hypovirulence.
Source & Citations
- Thesis Title: Molecular and Biological Characterization of Mycovirus Identified from Environmental Fungal Isolates
- Researcher: Wajeeha Shamsi
- Guide (Supervisor): Dr. Muhammad Faraz Bhatti
- University: Atta-ur-Rahman School of Applied Biosciences, National University of Sciences & Technology (NUST), Islamabad, Pakistan
- Year of Compilation: 2020
- Excerpt Page Numbers: 14, 49, 50, 114, 115, 118, 119
Disclaimer: Some sentences have been lightly edited for SEO and readability. For the full, original research, please refer to the complete thesis PDF linked in the section above.
Join the Discussion!
As next-generation sequencing reveals thousands of new viruses, do you think our current system of virus classification can keep up? Share your thoughts on the future of virus taxonomy below!
Discover more from Professor Of Zoology
Subscribe to get the latest posts sent to your email.