Cydia pomonella granulovirus
Description and Significance
Granuloviruses are in the family of insect viruses called the baculoviridae. These viruses target insects and are popular as insecticides for farmers targeting Lepidopteran larva. These viruses are popular due to their selectivity of only attacking insects from this particular order. Granuloviruses occlusion bodies contain one or rarely two virions, and are about 0.16-0.30 um by 0.30-0.50 um in size. The nucleocapsid of the virus contains a double-stranded circular-shaped strand of DNA (Fields virology). The outside of the nucleocapsid contains proteins that form ring-shaped subunits through their interactions. The end of the virion contains many unique proteins that are not found anywhere else in the virion, including the protein pp78/83 which aids in assembly of actin and production of offspring viruses. Occlusion bodies (Occluded virus, or OV) of granuloviruses contain one or two virions that are wrapped in a protein called granulin (a protein that distinguishes granuloviruses from nuclear polyhedrosis viruses). Occlusion bodies are crystalline gene products that are responsible for the primary viral infection. Their function is to release nucleocapsids into gut epithelial cells during infection. These occlusion bodies are oval shaped and referred to as 'granules' due to their appearance under a microscope. (Fields Virology). Granuloviruses also encode homologs of LD130, an envelope fusion protein (1). Granulovirus replication is biphasic cycle, where the budded viruses are formed prior to the occlusion viruses. Budded viruses are produced after primary infection and are simply nucleocapsids surrounded by a membrane. Their function is for cell-to-cell transmission of granulovirus.
CpGV is a double stranded DNA virus with a circular genome. The genome is 123,500 bases with 143 open reading frames. 25 of the genes are unique to CpGV, while 118 are homologous to other Baculovirus species. CpGV encodes six genes required for genome replication, which includes DNA polymerase and helicase. It has genes for granulin/polyhedrin, which is a major protein involved in the formation of viral inclusion bodies. Auxiliary genes include proteases, such as chitinase, which are dedicated to the degradation of host structures and the prevention of host cell death (Luque et al, 2001).
Ecology and Pathogenesis
Granulosis was discovered in the early 1960’s, and was found to only infect the codling moth (C. pomonella) and species closely related to it. The codling moth bores into apples, which makes them unfit for human consumption. Spraying apples with granulosis virus significantly decreased the amount of damaged apples, and killed most codling moth larvae before they could enter the fruit; most died after feeding on the epidermis of the treated fruits, which are still suitable for human consumption (Falcon et al, 1968).
The occluded form of the virus is consumed by hosts off of leaves, where it is released in the alkali environment of the C. pomonella larva midgut (Summers, 1971). The occluded form is responsible for primary infection, which occurs in gut basal cells of the larva. The cells endocytose the virus, which uncoats and releases its genome at the nuclear pores. The genome is then incorporated into the host genome, and is transcribed by host machinery. The assembled virus buds off of the opposite side of gut lumen cells, where it is released to infect the rest of the organism. This form of the virus, the budded form, is responsible for secondary infection within the host. Granulosis encodes proteases such as chitinase that degrade host proteins and liquify the host, which is the cause of its death (Luque et al, 2001).
A.J. Sauer, et. al. Novel resistance to Cydia pomonella granulovirus (CpGV) in codling moth shows autosomal and dominant inheritance and confers cross-resistance to different CpGV genome groups. PLOS ONE. 22 June 2017.
Page authored by Ben Kelly and Ilise Kundel, student of Prof. Jay Lennon at IndianaUniversity.