Downloaded from www.microbiologyresearch.org by IP: 107.22.5.19 On: Thu, 02 Mar 2017 14:46:48 A naturally occurring recombinant DNA-A of a typical bipartite begomovirus does not require the cognate DNA-B to infect Nicotiana benthamiana systemically Rafaelo M. Galva ˜o, 1 Andrea C. Mariano, 1 Dirce F. Luz, 1 Poliane F. Alfenas, 1 Eduardo C. Andrade, 1 Francisco M. Zerbini, 2 Ma ´ rcia R. Almeida 1 and Elizabeth P. B. Fontes 1 Correspondence Elizabeth Fontes bbfontes@ufv.br Departamento de Bioquı ´mica e Biologia Molecular 1 and Departamento de Fitopatologia/ BIOAGRO 2 , Universidade Federal de Vic ¸osa, Av. PH Rolfs s/n, 36571.000 Vic ¸ osa-MG, Brazil Received 16 August 2002 Accepted 18 November 2002 Species of the genus Begomovirus (family Geminiviridae) found in the western hemisphere typically have a bipartite genome that consists of two 2?6 kb DNA genomic components, DNA-A and DNA-B. We have identified and cloned genomic components of a new tomato-infecting begomovirus from Brazil, for which the name Tomato crinkle leaf yellows virus (TCrLYV) is proposed, and a DNA-A variant of Tomato chlorotic mottle virus (ToCMV-[MG-Bt1]). Sequence analysis revealed that TCrLYV was most closely related to ToCMV, although it was sufficiently divergent to be considered a distinct virus species. Furthermore, these closely related viruses induce distinguishable symptoms in tomato plants. With respect to ToCMV-[MG-Bt1] DNA-A, evidence is presented that suggests a recombinant origin. It possesses a hybrid genome on which the replication compatible module (AC1 and replication origin) was probably donated by ToCMV- [BA-Se1] and the remaining sequences appear to have originated from Tomato rugose mosaic virus (ToRMV). Despite the high degree of sequence conservation with its predecessors, ToCMV-[MG- Bt1] differs significantly in its biological properties. Although ToCMV-[MG-Bt1] DNA-A did not infect tomato plants, it systemically infected Nicotiana benthamiana, induced symptoms of mottling and accumulated viral DNA in the apical leaves in the absence of a cognate DNA-B. The modular rearrangement that resulted in ToCMV-[MG-Bt1] DNA-A may have provided this virus with a more aggressive nature. Our results further support the notion that interspecies recombination may play a significant role in geminivirus diversity and their emergence as agriculturally important pathogens. INTRODUCTION Geminiviruses (family Geminiviridae) are a large and diverse group of plant viruses characterized by their unique paired- icosahedral capsids (Lazarowitz, 1992). They have circular, single-stranded DNA genomes that replicate via double- stranded DNA intermediates in the nuclei of infected cells (Hanley-Bowdoin et al., 1999). The members of the Geminiviridae can be classified into four genera according to their host-range properties, insect vector and genome organization, which may be in either single or double- component configuration (Rybicki et al., 2000). The Begomovirus genus is the largest genus of this family and comprises the whitefly-transmitted geminiviruses that infect dicotyledonous plants. Begomoviruses found in the western hemisphere typically have bipartite genomes, whereas several monopartite begomoviruses have been identified in the eastern hemisphere, such as Tomato yellow leaf curl virus (TYLCV; Kheyr-Pour et al., 1991; Navot et al., 1991) and Tomato leaf curl virus (ToLCV; Dry et al., 1993), among others. The genome of the bipartite begomoviruses is split between two genomic components, designated DNA-A and DNA-B (Lazarowitz, 1992). Both components are organized into divergent transcription units separated by an intergenic region (IR) of about 200 bp, which contains the replication origin and two divergent promoters (Hanley-Bowdoin et al., 1999). DNA-A has the potential to code for five gene products (AV1, AC1, AC2, AC3, AC4) and DNA-B encodes two gene products (BV1 and BC1). Genetic and biochemical studies of viral genes and proteins have provided insights into their function. The AV1 gene product or CP represents the coat protein (Kallender et al., 1988), necessary for insect transmission (Azzam et al., 1994). The AC1 protein or Rep (replication-associated protein) is a sequence-specific DNA-binding protein essential for replication of both DNA- A and DNA-B genomic components (Elmer et al., 1988; 0001-8783 G 2003 SGM Printed in Great Britain 715 Journal of General Virology (2003), 84, 715–726 DOI 10.1099/vir.0.18783-0