The Incredible Journey of Begomoviruses in Their Whitefly Vector

Abstract

Begomoviruses are vectored in a circulative persistent manner by the whitefly Bemisia tabaci. The insect ingests viral particles with its stylets. Virions pass along the food canal and reach the esophagus and the midgut. They cross the filter chamber and the midgut into the haemolymph, translocate into the primary salivary glands and are egested with the saliva into the plant phloem. Begomoviruses have to cross several barriers and checkpoints successfully, while interacting with would-be receptors and other whitefly proteins. The bulk of the virus remains associated with the midgut and the filter chamber. In these tissues, viral genomes, mainly from the tomato yellow leaf curl virus (TYLCV) family, may be transcribed and may replicate. However, at the same time, virus amounts peak, and the insect autophagic response is activated, which in turn inhibits replication and induces the destruction of the virus. Some begomoviruses invade tissues outside the circulative pathway, such as ovaries and fat cells. Autophagy limits the amounts of virus associated with these organs. In this review, we discuss the different sites begomoviruses need to cross to complete a successful circular infection, the role of the coat protein in this process and the sites that balance between virus accumulation and virus destruction.

Prospects, challenges and current status of RNAi through insect feeding

“…The filter chamber is intended to move high volumes of liquids and not slower processing of solids as in chewing insects. Arguably, an insect with chewing mouthparts would have more time for the dsRNA to be absorbed by the midgut compared to a sap‐sucking insect . In another study, a comparison of knockdown effects was made between siRNAs fragments and their full‐length dsRNA parents.…”

“…Arguably, an insect with chewing mouthparts would have more time for the dsRNA to be absorbed by the midgut compared to a sap-sucking insect. 68 In another study, a comparison of knockdown effects was made between siRNAs fragments and their full-length dsRNA parents. Feeding full-length pheromone biosynthesis activating neuropeptide (PBAN) dsRNAs to Helicoverpa zea and Heliothis virescens showed delayed larval growth and more than ∼75% mortality in both, whereas siRNA treatments showed only ∼55% mortality.…”

A single amino acid substitution in the movement protein enables the mechanical transmission of a geminivirus

“…For mesophyll‐invading begomoviruses, MP is thought to take over viral DNA from NSP after being exported from the nucleus to the cytoplasm and deliver it to adjacent cells. Most nonmechanically transmissible begomoviruses have been reported to be phloem limited because they can be introduced into the phloem translocation stream through the stylets of insects and become systemic (Czosnek et al , ). One of the reasons that ToLCNDV‐CB fails to be mechanically transmissible and to initiate systemic infection after sap inoculation may be its inability to travel beyond the site of inoculation.…”

CRISPR/Cas9-based genome editing in the silverleaf whitefly (Bemisia tabaci)

“…Finally, B. tabaci is an important vector of numerous plant viruses that affect economically critical crop species. B. tabaci is the only known vector of begomoviruses, a family of plant viruses known to cause plant diseases and adversely affect crop yield (2). Current control methods for B. tabaci are insecticides, and limited use of biological control (3,4).…”