Virus Research 163 (2012) 169–177 Contents lists available at SciVerse ScienceDirect Virus Research journal homepage: www.elsevier.com/locate/virusres Molecular interaction between two cassava geminiviruses exhibiting cross-protection R.V. Chowda Reddy a,b , Wubei Dong a , Thomas Njock a,c , M.E.C. Rey d , Vincent N. Fondong a,∗ a Department of Biological Sciences, Delaware State University, 1200 North DuPont Highway, Dover, DE 19901, United States b Agriculture and Agri-Food Canada, 1391, Sandford St, London, Ontario, Canada N5V 4T3 c Faculty of Science, Department of Life Sciences, University of Buea, Buea, Cameroon d School of Molecular and Cell Biology, University of the Witwatersrand, Gatehouse, Room 001, Private Bag 3, PO Wits 2050, Braamfontein, Johannesburg, South Africa article info Article history: Received 18 July 2011 Received in revised form 6 September 2011 Accepted 6 September 2011 Available online 12 September 2011 Keywords: Cassava geminiviruses Cross-protection trans-Replication Recovery abstract There are increasing reports of geminivirus mixed infections of field plant hosts. These mixed infections have been suggested to result in recombinations, emergence of new viruses and new disease epidemics. We previously reported the occurrence of mixed infection between African cassava mosaic virus (ACMV) and East African cassava mosaic Cameroon virus (EACMCV) resulting in severe symptoms in cassava fields in Cameroon. Here, we show that reassortment of DNA-A and DNA-B components of ACMV and EACMCV does not form viable recombinants. However, in the presence of both components of either virus, the DNA-A component of the other virus replicated and spread in the absence of its DNA-B component. This result suggests that failure of ACMV and EACMCV to form viable recombinants is due to the inability of each DNA-A component to trans-replicate the heterologous DNA-B component. This study also shows that ACMV DNA-A induces a resistance to ACMV and EACMCV as indicated by absence or late symp- tom development. Moreover, this resistance enabled plants to recover from severe symptoms caused by EACMCV in Nicotiana benthamiana, suggesting that the resistance induced is not specific to ACMV and is consistent with the phenomenon of cross-protection between related viruses. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Cassava geminiviruses (family Geminiviridae, genus Bego- movirus) are associated with the cassava mosaic disease (CMD) occurring in cassava (Manihot esculenta) in Africa and southeastern Asia. Genomes of viruses belonging to the genus Begomovirus are either monopartite or bipartite (DNA-A and DNA-B components). For bipartite begomoviruses such as East African cassava mosaic Cameroon virus (EACMCV) (Fig. 1), DNA-A contains six genes: two in the sense and four complementary sense orientations, respec- tively. The sense orientation contains AV1 gene, which encodes the coat protein (CP) (Hamilton et al., 1984) and AV2 gene, which encodes the AV2 protein. The complementary sense orientation genes are AC1, which encodes the replication-associated protein (Rep) (Hanley-Bowdoin et al., 1990), AC2 and AC3, which encode the transcription activation protein (TrAP) (Sunter and Bisaro, 1991) and the replication enhancer protein (REn) (Hanley-Bowdoin et al., 1990) and AC4, which encodes the AC4 protein and is located within AC1. DNA-B codes for two genes, BC1 and BV1, which encode the movement protein (MP) and the nuclear shuttle protein (NSP), ∗ Corresponding author. Tel.: +1 302 857 7377; fax: +1 302 857 6512. E-mail address: vfondong@desu.edu (V.N. Fondong). respectively (Brough et al., 1988; Etessami et al., 1988; Sanderfoot et al., 1996). So far, several distinct virus species have been shown to be asso- ciated with CMD, namely African cassava mosaic virus (ACMV), East African cassava mosaic Cameroon virus (EACMCV), East African cas- sava mosaic virus (EACMV), East African cassava mosaic Kenya virus (EACMKV), East African cassava mosaic Malawi virus (EACMMV), East African cassava mosaic Zanzibar virus (EACMZV) and South African cassava mosaic virus (SACMV) in Africa, and Sri Lankan cassava mosaic virus (SLCMV) and Indian cassava mosaic virus (ICMV) in the Indian subcontinent (Rothenstein et al., 2005). Mixed infections by begomoviruses have been shown to result in recombinations and reassortment of viral components resulting in emergence of new virus species (Fondong et al., 2000a; Pita et al., 2001; Rasheed et al., 2006). Recombinant begomoviruses have been associated with severe epidemics in cassava (Pita et al., 2001; Fondong et al., 2000a), cotton (Idris and Brown, 2002), and tomato (Garcia-Andres et al., 2006, 2007; Monci et al., 2002). There is evidence that compo- nent reassortment is a contributing factor to cassava mosaic disease (Pita et al., 2001), and there are examples of monopartite bego- moviruses acquiring DNA-B components (Saunders et al., 2002). Formation of viable pseudorecombinant viruses through com- ponent reassortment has been observed in bipartite begomoviruses that have similar Rep—binding sites, such as in Tomato mottle Taino 0168-1702/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.virusres.2011.09.009