Identification and Characterization of a Novel Emaravirus Associated With Jujube (Ziziphus jujuba Mill.) Yellow Mottle Disease.

Caixia Yang,Song Zhang,Francesco Di Serio,Jingjing Fu,Tong Han,Mengji Cao

doi:10.3389/fmicb.2019.01417

Abstract

A previously unreported disease affecting jujube (Ziziphus jujuba Mill.) trees was observed in China (Liaoning province) in 2015 and named jujube yellow mottle disease (JYMD), due to prevalent symptoms on the leaves. Diseased plants produced also malformed and discolored fruits. In an attempt to identify the possible causal agent of JYMD, high-throughput sequencing of small RNA libraries was performed and a novel virus, tentatively named jujube yellow mottle-associated virus (JYMaV), was identified and characterized. Six genomic RNA segments of JYMaV were completely sequenced. Each one contains a single open reading frame in the viral complementary strand and two untranslated regions with complementary 5′ and 3′ terminal ends, thus showing typical features of other negative-stranded RNA viruses. RNA1 (7.1 kb), RNA2 (2.2 kb) and RNA3 (1.2 kb) encode putative proteins that, based on their conserved motifs, have been identified as the RNA dependent RNA polymerase, the glycoprotein and the nucleocapsid protein, respectively. These proteins share significant sequence identity (52.1–70.4%) with proteins encoded by raspberry leaf blotch virus (RLBV). RNA4 (1.5 kb) and RNA5 (1.2 kb) code for two putative 30 K movement proteins also related to the homologous RLBV protein. The functional role of the protein encoded by JYMaV RNA6 remains unknown. These data together with the phylogenetic relationships of JYMaV with other recognized emaraviruses support the proposal that JYMaV is the representative member of a novel species in the genus Emaravirus. In agreement with this proposal, virus-like particles and double-membrane-bound bodies, similar to those previously reported for other emaraviruses, were observed by transmission electron microscopy in extracts and tissues from symptomatic leaves, respectively. A specific RT-PCR-based detection method has been developed and used in a preliminary field survey that provided results strongly supporting the close association of JYMaV with the novel disease.

Highlights

Symptom Description In September 2015, jujube trees displaying symptoms of a disease apparently not reported previously were found in Chaoyang City, Liaoning Province
To investigate the etiology of jujube yellow mottle disease (JYMD), a new virus-like disease affecting jujube trees observed for the first time in 2015 in Liaoning province, we first sequenced by HTS small RNA libraries from symptomatic and symptomless jujube plants and, implemented these analyses with data from RNA-seq of an rRNAs-depleted total RNA library from a symptomatic plant
RNA 1, 2, 3, and 4 of jujube yellow mottle-associated virus (JYMaV) encode proteins that share the highest sequence identity with those encoded by the corresponding RNAs of raspberry leaf blotch virus (RLBV)

Summary

Introduction

European mountain ash ringspot-associated virus (EMARaV), rose rosette virus (RRV), fig mosaic virus (FMV), pigeonpea sterility mosaic virus and pigeonpea sterility mosaic virus (PPSMV and PPSMV-2), High Plains wheat mosaic virus (HPWMoV), raspberry leaf blotch virus (RLBV), redbud yellow ringspot-associated emaravirus (RYRaV), and actinidia chlorisis ringspot-associated virus (AcCRaV) (Mielke-Ehret and Mühlbach, 2007; Elbeaino et al, 2009a,b, 2014, 2015; Laney et al, 2011; Ishikawa et al, 2012; McGavin et al, 2012; Tatineni et al, 2014; Di Bello et al, 2015, 2016; Lu et al, 2015; Zheng et al, 2016) are representative members of the nine virus species included in the genus Emaravirus of the family Fimoviridae, order Bunyavirales (Maes et al, 2019). The recently discovered blackberry leaf mottle-associated virus (BLMaV) (Hassan et al, 2017) and Palo verde witches broom virus (PVWBV) (Ilyas et al, 2018) have Emaravirus attributes but they have not been officially classified yet These plant-infecting viruses have various modes of transmission including eriophyid mites, seeds (rare), grafting, mechanical friction and contaminated cutting implements. In the case of RLBV, it has been shown that these non-structural proteins may interact with each other and/or with the NP, with evidence of their involvement in viral pathogenesis provided for some of them (Lu et al, 2015) It is unclear how many RNA components are necessary for the emaravirus infectivity

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Conclusion