The Proteins and Functions of Plant Pararetroviruses: Knowns and Unknowns

Abstract

Two main classes of plant pararetroviruses exist: the icosahedral caulimoviruses and the bacilliform badnaviruses. In addition, the icosahedral cassava vein mosaic virus might constitute a separate group, because it differs from the other caulimoviruses in several aspects. Both groups of viruses contain genes homologous to the gag and pol genes of animal retroviruses. The genes for insect transmission and movement, on the other hand, have no counterparts in retroviruses but are related to the corresponding genes of plant RNA viruses. In addition, caulimoviruses, and probably the rice tungro badnavirus, have regulatory genes. The architecture and functions of the plant pararetrovirus gene products are compared and discussed.

Key Words:

• caulimovirus
• badnavirus
• movement
• insect transmission
• capsid
• reverse transcriptase
• RNAse H
• protease
• translation regulation
• nuclear import
• nuclear export