Geminiviruses

Geminiviruses are a genus of small, single-stranded DNA viruses in the family Geminiviridae. They are known for their distinctive, geminate (twin) virion structure, which is roughly spherical when viewed under an electron microscope but is actually composed of two incomplete, tightly associated particles. These viruses infect a wide range of plants, including many important crops, and can cause significant agricultural losses due to the diseases they induce.

The genome of geminiviruses consists of one or two circular DNA molecules, typically ranging from 2.5 to 5.2 kilobases in size. Depending on the species, the genome can be monopartite (single DNA molecule) or bipartite (two DNA molecules, usually designated DNA-A and DNA-B). These DNA molecules encode several proteins essential for viral replication, movement within the plant, and encapsidation.

Replication of geminiviruses occurs in the nucleus of plant cells. Upon infection, the viral DNA is transported to the nucleus, where it is replicated using host cell machinery and viral proteins. Geminiviruses are known for their ability to move bidirectionally within the plant, both systemically through the phloem and locally between cells. This movement is facilitated by specific viral proteins.

Geminivirus diseases manifest in various ways, often including leaf curling, yellowing (chlorosis), stunting, and mosaic patterns on foliage. Examples of economically important geminivirus diseases include tomato yellow leaf curl disease, maize streak disease, and bean golden yellow mosaic disease. Transmission of these viruses is primarily mediated by insect vectors, most commonly whiteflies and leafhoppers. Control strategies often focus on managing insect populations and developing virus-resistant crop varieties.