Infectious clones of Tomato leaf curl Palampur virus with a defective DNA B and their pseudo-recombination with Tomato leaf curl New Delhi virus.

Aamir Humayun Malik,Rob W Briddon,Shahid Mansoor

doi:10.1186/1743-422x-8-173

Aamir Humayun Malik, Rob W Briddon + Show 1 more

Open Access

https://doi.org/10.1186/1743-422x-8-173

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Abstract

BackgroundTomato leaf curl Palampur virus (ToLCPMV) is a bipartite begomovirus which has been reported from India and Iran but infectious clones have not been obtained. We have previously shown the association of Zucchini yellow mosaic virus (ZYMV), a potyvirus, with severe leaf curl disease of muskmelon in Pakistan. However, the severity of symptoms in the field and yield losses led us to believe that some other agent, such as a begomovirus, could be associated with the disease.ResultsA bipartite begomovirus associated with a severe yellow leaf curl disease on muskmelon in Pakistan has been characterized. Analysis of the complete nucleotide sequence of the DNA A and DNA B components of the begomovirus showed that it has the highest DNA sequence identity with ToLCPMV. However, the gene encoding the nuclear shuttle protein (NSP) was truncated in comparison to previously characterised isolates. Agrobacterium-mediated inoculation of Nicotiana benthamiana with the ToLCPMV clones obtained here did not result in symptoms. However, inoculation of plants with the DNA A component of ToLCPMV and the DNA B component of Tomato leaf curl New Delhi virus (ToLCNDV) lead to systemic infection with leaf curl symptoms. This suggested that the lack of infectivity of the ToLCPMV clones was due to the defect in DNA B. The DNA B of ToLCPMV was able to move systemically when inoculated with DNA A of the either virus. Agro-infiltration of muskmelon with the DNA A and DNA B components of ToLCPMV did not lead to symptomatic infection whereas inoculation with the DNA A with the DNA B of ToLCNDV resulted in a hypersensitive response (HR) along the veins. Additionally, agro-infiltration of muskmelon with a construct for the expression of the NSP gene of ToLCNDV under the control of the cauliflower mosaic virus 35S promoter induced a HR, suggesting that this is the gene causing the HR.ConclusionsBoth ToLCPMV and ZYMV are associated with muskmelon leaf curl disease in Pakistan. However, the ToLCPMV variant identified in association with ZYMV has a defective NSP. The results suggest that a variant with a defective NSP may have been selected for in muskmelon, as this protein is an avirulence determinant in this species, and possibly that infection requires the synergistic interaction with ZYMV.

Highlights

Tomato leaf curl Palampur virus (ToLCPMV) is a bipartite begomovirus which has been reported from India and Iran but infectious clones have not been obtained
Old World begomoviruses encode four open reading frames (ORFs) in the complementary-sense that are involved in viral DNA replication and control of gene expression, while two ORFs in the virion-sense are involved in virus encapsidation and movement
The two proteins encoded by the DNA B component are the nuclear shuttle protein (NSP) and the movement protein (MP) that are involved in nuclear transport and cell-to-cell movement of viral DNA, respectively [9]

Summary

Introduction

Tomato leaf curl Palampur virus (ToLCPMV) is a bipartite begomovirus which has been reported from India and Iran but infectious clones have not been obtained. We have previously shown the association of Zucchini yellow mosaic virus (ZYMV), a potyvirus, with severe leaf curl disease of muskmelon in Pakistan. Viruses of the family Geminiviridae have circular singlestranded (ss) DNA genomes, encapsidated in characteristic twinned isometric particles. These viruses are classified into four genera, Mastrevirus, Curtovirus, Topocuvirus and Begomovirus [2] depending upon their insect vector, host. The DNA A and DNA B components of begomoviruses encode genes both in the virion and complementary-sense orientations. Old World begomoviruses encode four open reading frames (ORFs) in the complementary-sense that are involved in viral DNA replication and control of gene expression, while two ORFs in the virion-sense are involved in virus encapsidation and movement. The two proteins encoded by the DNA B component are the nuclear shuttle protein (NSP) and the movement protein (MP) that are involved in nuclear transport and cell-to-cell movement of viral DNA, respectively [9]

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