The GroEL protein of the whitefly Bemisia tabaci interacts with the coat protein of transmissible and nontransmissible begomoviruses in the yeast two-hybrid system

We have previously suggested that a GroEL homolog produced by the whitefly Bemisia tabaci endosymbiotic bacteria interacts in the insect hemolymph with particles of Tomato yellow leaf curl virus from Israel (TYLCV-Is), ensuring the safe circulative transmission of the virus. We have now addressed the question of whether the nontransmissibility of Abutilon mosaic virus from Israel (AbMV-Is) is related to a lack of association between GroEL and the virus coat protein (CP). Translocation analysis has shown that, whereas TYLCV-Is DNA is conspicuous in the digestive tract, hemolymph, and salivary glands of B. tabaci 8 h after acquisition feeding started, AbMV-Is DNA was detected only in the insect digestive tract, even after 96 h. To determine whether AbMV-Is particles were rapidly degraded in the hemolymph as a result of their inability to interact with GroEL, we have isolated a GroEL gene from B. tabaci and used a yeast two-hybrid assay to compare binding of the CP of TYLCV-Is and AbMV-Is to the insect GroEL. The yeast assay showed that the CPs of the two viruses are able to bind efficiently to GroEL. We therefore suggest that, although GroEL-CP interaction in the hemolymph is a necessary condition for circulative transmission, the nontransmissibility of AbMV-Is is not the result of lack of binding to GroEL in the B. tabaci hemolymph, but most likely results from an inability to cross the gut/hemolymph barrier. (C) 2000 Academic Press.