Begomovirus

Begomovirus is a genus of viruses, in the family Geminiviridae.^[1] They are plant viruses that as a group have a very wide host range, infecting dicotyledonous plants. Worldwide they are responsible for a considerable amount of economic damage to many important crops such as tomatoes, beans, squash, cassava and cotton.^[2] There are 445 species in this genus.^[1]

Virus particles are non-enveloped. The nucleocapsid is 38 nanometers (nm) long and 15–22 nm in diameter. While particles have basic icosahedral symmetry, they consist of two incomplete icosahedra—missing one vertex—joined together. There are 22 capsomeres per nucleocapsid.

Single stranded closed circular DNA. Many begomoviruses have a bipartite genome: this means that the genome is segmented into two segments (referred to as DNA A and DNA B) that are packaged into separate particles. Both segments are generally required for successful symptomatic infection in a host cell but DNA B is dependent for its replication upon DNA A, which can in some begomoviruses apparently cause normal infections on its own.

The DNA A segment typically encodes five to six proteins including replication protein Rep, coat protein and transport and/or regulatory proteins. This component is homologous to the genomes of all other geminiviruses. The proteins encoded on it are required for replication (Rep), control of gene expression, overcoming host defenses, encapsidation (coat protein) and insect transmission. The DNA B segment encodes two different movement proteins. These proteins have functions in intra- and intercellular movement in host plants.

The A and B components share little sequence identity with the exception of a ~200 nucleotide sequence with typically >85% identity known as the common region. This region includes an absolutely conserved (among geminiviruses) hairpin structure and repeated sequences (known as 'iterons') that are the recognition sequences for binding of the replication protein (Rep). Within this loop there is a nonanucleotide sequence (TAATATTAC) that acts as the origin (ori) of virion strand DNA replication.

Component exchange (pseudorecombination) occurs in this genus.^[3] The usual mechanism of pseudorecombination is by a process known as 'regulon grafting': the A component donates its common region by recombination to the B component being captured. This results in a new dependent interaction between two components.

Begomovirus

Symptom of pepper yellow leaf curl virus