A GroEL Homologue from Endosymbiotic Bacteria of the WhiteflyBemisia tabaciIs Implicated in the Circulative Transmission of Tomato Yellow Leaf Curl Virus

Abstract

Evidence for the involvement of aBemisia tabaciGroEL homologue in the transmission of tomato yellow leaf curl geminivirus (TYLCV) is presented. A ∼63-kDa protein was identified inB. tabaciwhole-body extracts using an antiserum raised against aphidBuchneraGroEL. The GroEL homologue was immunolocalized to a coccoid-shaped whitefly endosymbiont. The 30 N-terminal amino acids of the whitefly GroEL homologue showed 80% homology with that from different aphid species and GroEL fromEscherichia coli. Purified GroEL fromB. tabaciexhibited ultrastructural similarities to that of the endosymbiont from aphids andE. coli.In vitroligand assays showed that tomato yellow leaf curl virus (TYLCV) particles displayed a specific affinity for theB. tabaci63-kDa GroEL homologue. Feeding whiteflies anti-BuchneraGroEL antiserum before the acquisition of virions reduced TYLCV transmission to tomato test plants by >80%. In the haemolymph of these whiteflies, TYLCV DNA was reduced to amounts below the threshold of detection by Southern blot hybridization. Active antibodies were recovered from the insect haemolymph suggesting that by complexing the GoEL homologue, the antibody disturbed interaction with TYLCV, leading to degradation of the virus. We propose that GroEL ofB. tabaciprotects the virus from destruction during its passage through the haemolymph.