Identification of a Novel Circular Single-Stranded DNA Associated with Cotton Leaf Curl Disease in Pakistan

Abstract

Recent reports have suggested that cotton leaf curl virus (CLCuV), a geminivirus of the genus Begomovirus, may be responsible for cotton leaf curl disease in Pakistan. However, the causal agent of the disease remains unclear as CLCuV genomic components resembling begomovirus DNA A are unable to induce typical disease symptoms when reintroduced into plants. All attempts to isolate a genomic component equivalent to begomovirus DNA B have been unsuccessful. Here, we describe the isolation and characterisation of a novel circular single-stranded (ss) DNA associated with naturally infected cotton plants. In addition to a component resembling DNA A, purified geminate particles contain a smaller unrelated ssDNA that we refer to as DNA 1. DNA 1 was cloned from double-stranded replicative form of the viral DNA isolated from infected cotton plants. Blot hybridisation using probes specific for either CLCuV DNA or DNA 1 was used to demonstrate that both DNAs co-infect naturally infected cotton plants from different geographical locations. DNA 1 was detected in viruliferous Bemisia tabaci and in tobacco plants infected under laboratory conditions using B. tabaci, indicating that it is transmitted by whiteflies. Sequence analysis showed that DNA 1 is approximately half the size of CLCuV DNA but shares no homology, indicating that it is not a defective geminivirus component. DNA 1 has some homology to a genomic component of members of Nanoviridae, a family of DNA viruses that are normally transmitted by aphids or planthoppers. DNA 1 encodes a homologue of the nanovirus replication-associated protein (Rep) and has the capacity to autonomously replicate in tobacco. The data suggest that a nanovirus-like DNA has become whitefly-transmissible as a result of its association with a geminivirus and that cotton leaf curl disease may result from a mutually dependent relationship that has developed between members of two distinct DNA virus families that share a similar replication strategy.

An unusual alphasatellite associated with monopartite begomoviruses attenuates symptoms and reduces betasatellite accumulation

“…In summary, evidence provided here and elsewhere indicates that several types of alphasatellite are associated with begomovirus-betasatellite complexes (Briddon et al, 2004;Mansoor et al, 1999). However, a role for alphasatellites in disease aetiology or virulence has not been shown.…”

“…Monopartite begomoviruses are frequently associated with two classes of satellite molecule, referred to as alphasatellites (Briddon et al, 2004;Mansoor et al, 1999) or betasatellites , and thus far are exclusively found in the EH. However, recently alphasatellites have been identified in conjunction with WH bipartite begomoviruses (Paprotka et al, 2010;Romay et al, 2010).…”

Complexity of begomovirus and betasatellite populations associated with chilli leaf curl disease in India

“…Begomoviruses have been reported to be associated with ssDNA satellite molecules and/or satellite-like molecules, namely betasatellites and alphasatellites, respectively (Mansoor et al, 1999;Nawaz-ul-Rehman & Fauquet, 2009;Saunders et al, 2000). The majority of the Old World monopartite begomoviruses co-exist with betasatellites.…”

An Overview on Cotton Leaf Curl Disease: An Emerging Potential Threat to Cotton

“…A smaller (approx. 1350 nucleotides) single stranded DNA molecule (termed DNA-1) was shown to be associated with CLCuD (Mansoor et al, 1999). This molecule capable of self-replication in plant cells but requiring CLCuV for spread in plants as well as in insect transmission was shown to play no part in inducing symptoms.…”

“…They provide inoculum to the vector for transmitting the same in cotton. There are many ornamental plants and common weeds which have been found infected with whiteflytransmitted geminiviruses (Mansoor et al, 1998;Mansoor et al, 1999). Singh et al, (1994) reported appearance of the CLCuD on the Sidasps, Abutilon indicum, Hibiscus rosa-sinensis, and Althea roses on the basis of visual symptoms.…”