Totiviridae

Journal.ppat.1003225.g003.A.B

Totiviridae genome

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Totiviridae is a family of double-stranded RNA viruses that infect fungi, protozoa, and algae. Members of this virus family are known as totiviruses. The name "Totiviridae" is derived from the Latin word totus, meaning "whole" or "entire", referring to the complete capsid structure without an envelope. Totiviruses have a simple structure and genome, making them a subject of interest in virology for understanding the mechanisms of viral replication and host-virus interactions.

Classification

Totiviridae is classified into several genera, including Victorivirus, Giardiavirus, Leishmaniavirus, and Trichomonasvirus, among others. Each genus is distinguished by its host range and some specific genomic and structural characteristics. The classification is based on the International Committee on Taxonomy of Viruses (ICTV) standards.

Morphology

Viruses in the Totiviridae family are characterized by their icosahedral capsid structure with a diameter of approximately 40 nm. They lack an envelope, which is typical for many other types of viruses. The capsid encloses a double-stranded RNA genome, which is segmented in some species.

Genome

The genome of totiviruses is relatively small, ranging from 4.6 to 7 kilobases. It typically contains two open reading frames (ORFs). The first ORF encodes the capsid protein, necessary for the formation of the virus particle. The second ORF encodes the RNA-dependent RNA polymerase (RdRp), which is essential for the replication of the viral RNA genome. In some totiviruses, these ORFs overlap and are expressed as a fusion protein through a -1 ribosomal frameshift mechanism.

Life Cycle

The life cycle of Totiviridae involves several key steps. Initially, the virus attaches to the host cell and releases its RNA genome into the cytoplasm. The viral RdRp then synthesizes a complementary RNA strand, forming a double-stranded RNA genome. This genome serves as a template for the synthesis of viral proteins and for the replication of new viral RNA genomes. Assembly of new virus particles occurs in the cytoplasm, encapsidating the RNA genome. Totiviruses are then released from the host cell, typically without causing cell lysis, allowing for persistent infections.

Pathogenicity

Most totiviruses are not pathogenic to their hosts. In fungi, they are often associated with latent infections, with no apparent symptoms. However, some totiviruses can influence the phenotype of their host, such as the hypovirulence (reduced virulence) in certain pathogenic fungi. This characteristic has been explored for biological control purposes in agriculture.

Research and Applications

Research on Totiviridae has provided insights into the mechanisms of RNA virus replication, evolution, and host-virus interactions. The study of totiviruses in pathogenic fungi has also opened avenues for the development of biocontrol strategies to combat fungal diseases in crops.