Recombination, pseudorecombination and synergism of geminiviruses are determinant keys to the epidemic of severe cassava mosaic disease in Uganda

Abstract

The molecular variability of cassava geminiviruses occurring in Uganda was investigated in this study. Infected cassava plants and whiteflies were collected from cassava plantings in different geographical areas of the country and PCR was used for molecular characterization of the viruses. Two complete sequences of DNA-A and -B from African cassava mosaic virus (ACMV), two DNA-A sequences from East African cassava mosaic virus (EACMV), two DNA-B sequences of EACMV and the partial DNA-A nucleotide sequence of a new virus strain isolated in Uganda, EACMV-UG3, are reported here. Analysis of naturally infected cassava plants showed various assortments of DNA-A and DNA-B of the Ugandan viruses, suggesting the occurrence of natural inter-and intraspecies pseudorecombinations and a pattern of cassava mosaic disease (CMD) more complex than previously reported. EACMV-UG2 DNA-A, which contains a recombinant fragment between ACMV and EACMV-UG1 in the coat protein gene that resembles virus from Tanzania, was widespread in the country and always associated with EACMV-UG3 DNA-B, which probably resulted from another natural recombination event. Mixed infections of ACMV-UG and EACMV-UG in cassava and whiteflies were detected in most of the regions where both viruses occurred. These mixed-infected samples always showed extremely severe CMD symptoms, suggesting a synergistic interaction between ACMV-UG and EACMV-UG2. The first demonstration is provided of infectivity of EACMV clones to cassava, proving conclusively that the pseudorecombinant EACMV-UG2 DNA-AMEACMV-UG3 DNA-B is a causal agent of CMD in Uganda.

Supervirulent pseudorecombination and asymmetric synergism between genomic components of two distinct species of begomovirus associated with severe tomato leaf curl disease in India

“…Synergism between isolates of two cassava-infecting geminiviruses, ACMV and EACMV, has been observed and the genes mediating synergism have been identified (Fondong et al, 2000;Pita et al, 2001;Vanitharani et al, 2004). Synergism between ACMV and East African cassava mosaic Cameroon virus (EACMCV) is a two-way process, as the presence of the DNA-A component of ACMV or EACMCV enhanced the accumulation of viral DNA of EACMCV and ACMV, respectively, in tobacco BY2 protoplasts (Vanitharani et al, 2004).…”

“…Harrison et al (1997) suggested the possibility of synergism between isolates of the two cassava begomovirus species, African cassava mosaic virus and East African cassava mosaic virus. Molecular evidence for synergism between the cassava-infecting begomoviruses African cassava mosaic virus from Cameroon (ACMV- [CM:98]) and East African cassava mosaic virus from Cameroon (EACMV- [CM:98]) has been demonstrated (Fondong et al, 2000;Pita et al, 2001;Vanitharani et al, 2004).…”

Further molecular characterization of weed-associated begomoviruses in Brazil with an emphasis on Sida spp

“…Several studies have shown that recombination plays an important role in the generation of genetic variability in begomoviruses in Brazil (Galvão et al, 2003;Inoue-Nagata et al, 2006;Ribeiro et al, 2007;Silva et al, 2011a,b) and worldwide (Pita et al, 2001;Monci et al, 2002;García-Andrés et al, 2006, 2007a. Recombination analysis showed the occurrence of inter-and intraspecific recombination events in the Rep, CP and CR of the viral isolates detected in Sida spp.…”

Risks from GMOs due to Horizontal Gene Transfer

“…New, highly virulent, strains of African cassava mosaic virus ravage a critical African staple in an epidemic that is still expanding (Legg and Thresh, 2000). These new strains, which can overcome previously resistant lines of cassava, have emerged by recombination between viruses naturally co-existing in cassava (Pita et al, 2001;Zhou et al, 1997). In addition, mutation and recombination of viruses in the laboratory have generated offspring viruses with more severe pathology (Ding et al, 1996).…”