Roles and interactions of begomoviruses and satellite DNAs associated with okra leaf curl disease in Mali, West Africa

Abstract

Okra leaf curl disease (OLCD) is a major constraint on okra (Abelmoschus esculentus) production in West Africa. Two monopartite begomoviruses (okra virus-1 and okra virus-2), a betasatellite and a DNA1 satellite are associated with OLCD in Mali. Okra virus-1 is an isolate of okra yellow crinkle virus (OYCrV), okra virus-2 is a recombinant isolate of cotton leaf curl Gezira virus (CLCuGV) and the betasatellite is a variant of cotton leaf curl Gezira betasatellite (CLCuGB). Cloned DNA of OYCrV and CLCuGV were infectious and induced leaf curl symptoms in Nicotiana benthamiana plants, but did not induce OLCD in okra. However, when these clones were individually co-inoculated with the cloned CLCuGB DNA, symptom severity and viral DNA levels were increased in N. benthamiana plants and typical OLCD symptoms were induced in okra. The CLCuGB was also replicated by, and increased symptom severity of, three monopartite tomato-infecting begomoviruses, including two from West Africa. The sequence of the DNA1 satellite was highly divergent, indicating that it represents a distinct West African lineage. DNA1 replicated autonomously, and replication required the DNA1-encoded Rep protein. Although DNA1 reduced helper begomovirus DNA levels, symptoms were not attenuated. In the presence of CLCuGB, DNA levels of the helper begomoviruses and DNA1 were substantially increased. Together, these findings establish that OLCD in Mali is caused by a complex of monopartite begomoviruses and a promiscuous betasatellite with an associated parasitic DNA1 satellite. These findings are discussed in terms of the aetiology of OLCD and the evolution of new begomovirus/satellite DNA complexes.

Begomovirus disease complex: emerging threat to vegetable production systems of West and Central Africa

“…With the advent of more advanced molecular techniques in the study of begomoviruses, such as polymerase chain reaction (PCR), rolling cycle amplification (RCA)/restriction fragment length polymorphism (RFLP), and sequencing, the situation has greatly improved, leading to the identification of previously unknown begomovirus/satellite complexes infecting tomato, okra and pepper such as Tomato leaf curl Cameroon virus (ToLCCMV), Tomato leaf curl Nigeria virus (ToLCNGV), Tomato leaf curl Ghana virus (ToLCGHV), Tomato leaf curl Kumasi virus (ToLCKuV), and Tomato leaf curl Togo virus (ToLCTGV), which could collectively be termed the West African tomato-infecting begomoviruses (WATIBs) (Figure 3). Beside the WATIBs, others such as Tomato yellow leaf curl Mali virus (TYLCMLV), Pepper yellow vein Mali virus (PepYVMLV), and Tomato leaf curl Mali virus (ToLCMLV) have been identified infecting tomato and pepper in the region [49][50][51][52][53][54][55][56][57] (Figure 3 arrows). Apart from the pepper and tomato-infecting begomoviruses, others such as Cotton leaf curl Gezira virus (CLCuGeV), Okra leaf curl Cameroon virus (OLCuCMV), and Okra yellow crinkle virus (OYCrV) have been identified infecting okra in West and Central Africa [49,52,56,58] (Figure 3).…”

“…Beside the WATIBs, others such as Tomato yellow leaf curl Mali virus (TYLCMLV), Pepper yellow vein Mali virus (PepYVMLV), and Tomato leaf curl Mali virus (ToLCMLV) have been identified infecting tomato and pepper in the region [49][50][51][52][53][54][55][56][57] (Figure 3 arrows). Apart from the pepper and tomato-infecting begomoviruses, others such as Cotton leaf curl Gezira virus (CLCuGeV), Okra leaf curl Cameroon virus (OLCuCMV), and Okra yellow crinkle virus (OYCrV) have been identified infecting okra in West and Central Africa [49,52,56,58] (Figure 3). Putative recombination events were detected in begomovirus genomes for all three plant species studied, indicating that recombination is an important mechanism for their evolution.…”

Characterization of a New World Monopartite Begomovirus Causing Leaf Curl Disease of Tomato in Ecuador and Peru Reveals a New Direction in Geminivirus Evolution

“…Replication was assessed in N. benthamiana leaf discs as previously described (50). Infectivity and symptomatology of mutants in agroinoculated tomato (cultivar Glamour) and N. benthamiana plants were assessed as described previously.…”

“…Recombinant plasmids with the multimeric clones were identified by restriction enzyme digestion and transformed into competent Agrobacterium tumefaciens cells (strain C58C1) by using the freeze-thaw method (49 Assessment of viral DNA levels. Total genomic DNA was extracted from leaf tissue, and DNA gel blot hybridization analysis was conducted as previously described (50). Newly emerged leaves were collected from infected plants 21 and 60 dpi, total genomic DNA was extracted, and DNA gel blot hybridization analysis was conducted with a probe composed of the recombinant plasmids pPA98-1-1, pPA98-2-1, and pPA10-3 labeled with [␣- Immunolocalization experiments were conducted with leaf and petiole tissues collected from symptomatic tomato plants (cultivar Glamour) 4 weeks after agroinoculation with the multimeric PA98-1-1 and PA98-2-1 clones.…”

Mutational Analysis of Effectors Encoded by Monopartite Begomoviruses and Their Satellites

“…Several alphasatellites are capable of replicating and systemically infecting their plant host in the presence of a helper begomovirus without a visible effect on symptom development or virulence [6,40]. However AYVSGA a different type of 'DNA-2'-class alphasatellite that ameliorates symptom severity in an infected host and also capable of reducing virulence and the relative accumulation of its associated Tomato leaf curl betasatellite (ToLCB) [1].…”