The dsRNA Virus Papaya Meleira Virus and an ssRNA Virus Are Associated with Papaya Sticky Disease.

Josiane G. Amaral,Francisco Murilo Zerbini,Marcio Tadeu Godinho,Flávia O. Souza,Tathiana Ferreira Sá Antunes,Patricia Machado Bueno Fernandes,Poliane Alfenas Zerbini,Rogerio Margis,José Aires Ventura,Raquel J. Vionette Amaral

doi:10.1371/journal.pone.0155240

Abstract

Papaya sticky disease, or “meleira”, is one of the major diseases of papaya in Brazil and Mexico, capable of causing complete crop loss. The causal agent of sticky disease was identified as an isometric virus with a double stranded RNA (dsRNA) genome, named papaya meleira virus (PMeV). In the present study, PMeV dsRNA and a second RNA band of approximately 4.5 kb, both isolated from latex of papaya plants with severe symptoms of sticky disease, were deep-sequenced. The nearly complete sequence obtained for PMeV dsRNA is 8,814 nucleotides long and contains two putative ORFs; the predicted ORF1 and ORF2 display similarity to capsid proteins and RdRp's, respectively, from mycoviruses tentatively classified in the family Totiviridae. The sequence obtained for the second RNA is 4,515 nucleotides long and contains two putative ORFs. The predicted ORFs 1 and 2 display 48% and 73% sequence identity, respectively, with the corresponding proteins of papaya virus Q, an umbravirus recently described infecting papaya in Ecuador. Viral purification in a sucrose gradient allowed separation of particles containing each RNA. Mass spectrometry analysis indicated that both PMeV and the second RNA virus (named papaya meleira virus 2, PMeV2) were encapsidated in particles formed by the protein encoded by PMeV ORF1. The presence of both PMeV and PMeV2 was confirmed in field plants showing typical symptoms of sticky disease. Interestingly, PMeV was detected alone in asymptomatic plants. Together, our results indicate that sticky disease is associated with double infection by PMeV and PMeV2.

Highlights

Papaya sticky disease ("meleira" in Portuguese) was first reported in 1980 in the south of Bahia and north of Espírito Santo states of Brazil [1]
One group showed the lowest e-values with the putative structural protein of papaya meleira virus (PMeV)-RN (KT013296), and with the RNA-dependent RNA polymerase (RdRp)) protein of Phlebiopsis gigantea mycovirus double-stranded RNA (dsRNA)-2 (PgV-2; AM111097), a dsRNA virus related to members of family Totiviridae
The other group showed the lowest e-values with the RdRp of papaya virus Q (PpVQ; KP165407), a new papaya virus discovered in Ecuador and which, like PMeV-Mx, is related to members of the genus Umbravirus

Summary

Introduction

Papaya sticky disease ("meleira" in Portuguese) was first reported in 1980 in the south of Bahia and north of Espírito Santo states of Brazil [1]. A viral etiology of sticky disease was suggested by Kitajima et al, [7] following the observation of dsRNA-containing isometric particles in the laticiferous vessels of infected plants. The viral etiology was confirmed after healthy papaya plants inoculated with purified virus particles developed typical symptoms of the sticky disease [8]. It is unlikely that papaya sticky disease in Brazil and in Mexico, displaying similar symptoms, would have different viruses as causal agents. We hypothesized that PMeV and a second, umbra-like virus, could be involved in the disease To test this hypothesis, we deepsequenced RNA purified directly from latex samples, analyzed the association of different RNA molecules with the isometric particles found in the laticiferous vessels, and tested for the presence of these RNA molecules in symptomatic and symptomless field plants. A new etiology is proposed for papaya sticky disease: it is associated with a double infection with two viruses, PMeV and an ssRNA virus which is closely related to members of the genus Umbravirus

Ethics Statement

Results

Discussion