Abstract
Cotton leaf curl virus (CLCuV) (Gemininiviridae: Begomovirus) is the causative agent of leaf curl disease in cotton plants (Gossypium hirsutum). CLCuV is exclusively transmitted by the whitefly species B. tabaci (Gennadius) (Hemiptera: Alerodidae). B. tabaci contains several biotypes which harbor dissimilar bacterial endo-symbiotic community. It is reported that these bacterial endosymbionts produce a 63 kDa chaperon GroEL protein which binds to geminivirus particles and protects them from rapid degradation in gut and haemolymph. In biotype B, GroEL protein of Hamiltonella has been shown to interact with Tomato yellow leaf curl virus (TYLCV). The present study was initiated to find out whether endosymbionts of B. tabaci are similarly involved in CLCuV transmission in Sriganganagar (Rajasthan), an area endemic with cotton leaf curl disease. Biotype and endosymbiont diversity of B. tabaci were identified using MtCO1 and 16S rDNA genes respectively. Analysis of our results indicated that the collected B. tabaci population belong to AsiaII genetic group and harbor the primary endosymbiont Portiera and the secondary endosymbiont Arsenophonus. The GroEL proteins of Portiera and Arsenophonus were purified and in-vitro interaction studies were carried out using pull down and co-immunoprecipitation assays. In-vivo interaction was confirmed using yeast two hybrid system. In both in-vitro and in-vivo studies, the GroEL protein of Arsenophonus was found to be interacting with the CLCuV coat protein. Further, we also localized the presence of Arsenophonus in the salivary glands and the midgut of B. tabaci besides the already reported bacteriocytes. These results suggest the involvement of Arsenophonus in the transmission of CLCuV in AsiaII genetic group of B. tabaci.
Highlights
Geminiviruses are a group of plant viruses that infect a wide range of dicotyledonous crops
Cotton leaf curl virus (CLCuV) is a monopartite begomovirus belonging to family geminiviridae which causes leaf curl disease in cotton plants (Gossypium hirsutum)
Studies have shown that the GroEL protein of Buchnera aphidicola, endosymbiont of Myzus persicae binds to the luteovirus coat protein and protect virus particles from rapid proteolysis in gut and haemolymph [23]
Summary
Geminiviruses are a group of plant viruses that infect a wide range of dicotyledonous crops. B. tabaci is a sap sucking hemipteran insect belonging to family Aleyrodidae It is a polyphagous insect which can survive on more than 700 species of plants in 86 families and causes severe damage to crops both, directly by feeding and indirectly by transmitting plant viruses. B. tabaci feeds on phloem sap which, is rich in carbohydrates, but lacks essential amino acids These lacking nutrients are expected to be compensated by the bacterial community harbored by the insect [10]. There are contradictory reports about the role of endosymbionts in virus transmission, for example Bouvaine et al, [27] reported that GroEL protein secreted by Buchnera aphidicola the endosymbiont of Myzus persicae is found confined to the bacterial cells and is neither present in the haemolymph nor in the gut and fat body of the insect host
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