Geminiviridae

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Geminiviridae
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Family:	Geminiviridae

The Geminiviridae is a family of viruses known for their unique twin (geminate) particle morphology and their ability to infect a wide range of plant species. These viruses are of significant agricultural importance due to their impact on crop yields and quality.

Structure

Geminiviruses are characterized by their distinctive twin icosahedral particles, which are approximately 18-30 nm in diameter. Each particle consists of a single circular single-stranded DNA (ssDNA) genome, which is encapsidated within a protein coat. The genome size ranges from 2.5 to 3.0 kilobases, and in some genera, the genome is bipartite, consisting of two separate DNA molecules.

Genome Organization

The genome of geminiviruses is compact and encodes a limited number of proteins. These include:

• Replication-associated proteins: Involved in the replication of the viral DNA.
• Movement proteins: Facilitate the movement of the virus within the host plant.
• Coat proteins: Form the protective capsid around the viral genome.

The genome is organized into two main regions:

• The Replication Origin (ori): Contains sequences necessary for the initiation of DNA replication.
• The Coding Region: Contains overlapping open reading frames (ORFs) that encode the viral proteins.

Replication Cycle

Geminiviruses replicate through a rolling circle mechanism, which is initiated by the virus-encoded replication-associated protein. The replication occurs in the nucleus of the host cell and involves the synthesis of a complementary DNA strand to form a double-stranded DNA intermediate. This intermediate serves as a template for the production of new viral genomes.

Transmission

Geminiviruses are primarily transmitted by insect vectors, particularly whiteflies (Bemisia tabaci) and leafhoppers. The transmission is circulative and non-propagative, meaning the virus does not replicate within the vector but is carried from one plant to another.

Host Range and Symptoms

Geminiviruses have a broad host range, infecting both monocotyledonous and dicotyledonous plants. Infected plants often exhibit symptoms such as yellowing, stunting, leaf curling, and mosaic patterns, which can lead to significant agricultural losses.

Economic Impact

The economic impact of geminiviruses is substantial, particularly in tropical and subtropical regions where they affect staple crops such as cassava, tomato, and cotton. Management strategies include the use of resistant plant varieties, vector control, and cultural practices to reduce the spread of the virus.

Also see

• Begomovirus
• Curtovirus
• Topocuvirus
• Mastrevirus
• Plant virus
• Viral replication