segment's complementary ends. The L segment encodes the RNA-dependent RNA polymerase, necessary for viral RNA replication and mRNA synthesis. The M segment encodes the viral glycoproteins, which project from the viral surface and aid the virus in attaching to and entering the host cell. The S segment encodes the nucleocapsid protein (N). Most bunyaviruses have a negative-sense L and M segment. The S segment of the genus Phlebovirus, and both M and S segment of the genus Tospovirus are ambisense. Ambisense means that some of the genes on the RNA strand are negative sense and others are positive sense. The ambisense S segment codes for the viral nucleoprotein (N) in the negative sense and a nonstructural protein (NSs) in the positive sense. The ambisense M segment codes for glycoprotein (GP) in the negative sense and a nonstructural protein (NSm) in the positive sense. The total genome size ranges from 10.5 to 22.7 kbp. Life cycle The ambisense genome requires two rounds of transcription to be carried out. First, the negative-sense RNA is transcribed to produce mRNA and a full-length replicative intermediate. From this intermediate, a subgenomic mRNA encoding the small segment nonstructural protein is produced while the polymerase produced following the first round of transcription can now replicate the full-length RNA to produce viral genomes. Bunyaviruses replicate in the cytoplasm, while the viral proteins transit through the ER and Golgi apparatus. Mature virions bud from the Golgi apparatus into vesicles which are transported to the cell surface. Transmission Bunyaviruses infect arthropods, plants, protozoans, and vertebrates. Plants can host bunyaviruses from the families Tospoviridae and Fimoviridae (e.g. tomato, pigeonpea, melon, wheat, raspberry, redbud, and rose). Members of some families are insect-specific, for example the phasmavirids, first isolated from phantom midges, and since identified in diverse insects including moths, wasps and bees, and other true flies. Taxonomy There are 477 virus species recognised in this order. The phylogenetic tree diagram provides a full list of member species and the hosts which they infect. The order is organized into the following 12 families: Arenaviridae Cruliviridae Fimoviridae Hantaviridae Leishbunyaviridae Mypoviridae Nairoviridae Peribunyaviridae Phasmaviridae Phenuiviridae Tospoviridae Wupedeviridae Diseases in humans Bunyaviruses that cause disease in humans include: California encephalitis virus, Jamestown Canyon virus, La Crosse encephalitis virus, Oropouche orthobunyavirus, and Snowshoe hare virus (vector: mosquitoes; family: Peribunyaviridae); Hantavirus reservoir: small mammals or rodents (vector: aerosolized excreta from these mammals; family: Hantaviridae); Crimean–Congo hemorrhagic fever reservoir