Molecular Evidence for Association of Tobacco Curly Shoot Virus and a Betasatellite with Curly Shoot Disease of Common Bean (Phaseolus vulgaris L.) from India

Venkataravanappa V

doi:10.4172/2157-7471.1000148

Abstract

A new strain (FB01) of Tobacco curly shoot virus (TbCSV) showing curly shoot symptoms on common bean plants from Varanasi, Uttar Pradesh state of India was characterized. The analysis of the whole genome sequence and individual ORFs of this virus indicated that it is very closely related (sequence similarity of 89.1-94.5%) to the TbCSV infecting solanaceous and other weed crops in India and China. This was well supported by phylogenetic analysis with close clustering of the virus isolate with TbCSV. The absence of DNA-B and association of virus with betasatellite confirmed it as a monopartite begomovirus. The betasatellite identified here shared highest (53.9-93.9%) sequence identity with tomato leaf curl betasatellite. Further, putative recombination events were recognized within the virus sequence, suggesting that the virus is a recombinant and evolved from recombination of Tobacco curly shoot virus, Munbean yellow mosaic virus, Tomato leaf curl Jodhpur virus, Tobacco leaf curl Yunnan virus and Ageratum enation virus like ancestors. For betasatellite, the putative recombination events were recognized within the sequence, were interspecific. The new recombinant betasatellite was derived from recombination between Croton yellow vein mosaic betasatellite and Tomato yellow leaf curl China betasatellite, as the foremost parents in its evolution. The virus was transmitted by whiteflies as well as sap, and not by seed.

Highlights

The begomoviruses belong to the family Geminiviridae, are apparently evolving as rapidly as some RNA viruses [1]
The DNA-A in bipartite viruses and its homolog in monopartite viruses encodes pre-coat protein and coat protein in the sense strand, which are essential for transmission [3], and Replication-associated protein (Rep); the Replication Enhancer protein (REn) required for viral DNA replication; the Transcriptional Activator Protein (TrAP) required for gene expression control in the complementary strand
The genome organization is typical of other Old world monopartite Begomoviruses, comprising two Open Reading Frames (ORFs) [AV1 (CP), AV2] in virion-sense strand and four ORFs [AC1 (Rep), AC2, AC3, AC4] in complementary-sense strand, separated by an Intergenic Region (IR) (Table 1). Comparisons of this virus sequence with other reported Begomoviruses sequences revealed the present isolate infecting common bean have highest sequence identity (89.1-94.5%) with Tobacco curly shoot virus (TbCSV), found in India and China infecting solanaceous and other weed crops, while it shares less than 83% identity with rest of the Begomoviruses infecting pulses, tomato, tobacco, mesta and cotton. These results suggest that virus isolate-FB01 is an isolate of TbCSV (Table 2), based on the current criteria for classification of Begomoviruses [2]

Summary

Introduction

The begomoviruses belong to the family Geminiviridae, are apparently evolving as rapidly as some RNA viruses [1]. The Begomovirus is the largest genus of this family and comprises whitefly transmitted geminiviruses, infecting dicotyledonous plants [2]. The genomes of Begomoviruses consist of single component (Monopartite) or two components (Bipartite), which are having approximate size of 2.6-2.8 kb each. The DNA-A in bipartite viruses and its homolog in monopartite viruses encodes pre-coat protein and coat protein in the sense strand, which are essential for transmission [3], and Replication-associated protein (Rep); the Replication Enhancer protein (REn) required for viral DNA replication; the Transcriptional Activator Protein (TrAP) required for gene expression control in the complementary strand. DNA-B encodes proteins required for intracellular movement (BC1, BV1) and transport of viral ssDNA in the host plant [4,5]. The two components share a region of high sequence homology that is known as CR, the place from where the replication of the viral DNA genomes initiates

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