Next generation sequencing (NGS) has been widely applied to virus and viroid discovery in plants and animals. Compared to other NGS based methods that require viral enrichment and concentration, the small RNA sequencing (sRNA-seq) methods simplify virus detection and indeed have several other advantages [1] . The sRNA-seq based method was originally used for viral detection and identification in plants [2] and in invertebrates [3] . Although the sRNA-seq based method does not perform as well in the detection of mammalian viruses as in the detection of plant or invertebrate viruses, we still detected eight mammalian viruses: HPV-18 (Human Papillomavirus type 18) [4] , HBV (Hepatitis B Virus) [4] , HCV (Hepatitis C Virus) [4] , HIV-1 (Human Immunodeficiency Virus type 1) [4] , SMRV (Squirrel Monkey Retrovirus) [4] , EBV (Epstein-Barr Virus) [4] , SARS-CoV (Severe Acute Respiratory Syndrome Coronavirus) [5] and a DNA segment of ASFV (African Swine Fever Virus) [6] . The discovery of featured RNA fragments, including siRNA duplexes [7] , 5′ and 3′ end small RNAs (5′ and 3′ sRNAs) [8] [9] , palindromic small RNAs (psRNAs) and complemented palindromic small RNAs (cpsRNAs) [5] , has increased our capacity to detect viruses in mammals. Moreover, we found that 5′ and 3′ sRNAs can be used to annotate nuclear non-coding and mitochondrial genes at 1 bp resolution [10] [11] . Then, we found that 5′ and 3′ sRNAs can be used to obtain the full-length 5' and 3' ends of, but not limited to genome sequences of RNA viruses at 1-bp resolution.
Ticks transmit a great variety of infectious agents to humans and other animal species, including viruses of the Flaviviridae family among the most common tick-borne viruses [12] . With the development of NGS, a number of studies have used metagenomics to search for tick-associated pathogens [13] . However, the metagenomics methods using DNA can not be applied to detect RNA viruses without DNA stages. So the transcriptomics approaches using total RNA were also applied to detect tick viruses [14] . The sRNA-seq based method has been successfully used in the detection of Rickettsia in ticks [15] . As far as we know, there had not been previous reports of virus detection in ticks using the sRNA-seq based method until the detection of the DNA segment of ASFV [6] . Although very high-depth sRNA-seq data was used to detect a DNA segment of ASFV, the coverage of the ASFV reference genome was still very low. This suggested that the sRNA-seq based method does not perform as well in the detection of DNA viruses as in the detection of RNA viruses.
In our previous study [6] , we used sRNA-seq to detect viruses in ticks. Subsequent analyses of the detected viruses led to the discovery of a new strain of RNA virus. In 2014, this virus was first reported as a novel tick-borne virus of the genus Flavivirus from the Mogiana Region in Brazil [12] . Later, this virus was also named as Jingmen tick virus (JMTV), Kindia tick virus (KDTV) or Guangxi tick virus (GXTV) in some data from the NCBI GenBank database (Results and Discussion). In humans, viruses closely related to MGTV were found to be primarily associated with patients in Kosovo [16] . In the present study, we reported a new MGTV strain Yunnan2016 detected in Amblyomma testudinarium ticks [17] and also aimed to achieve the following research goals: (1) prove the feasibility of using the sRNA-seq based method in the detection of viruses in a sample (two ticks) containing miniscule RNA; (2) show how to obtain the full-length genome sequence of a RNA virus using sRNA-seq data; and (3) to provide a high-quality and well curated reference genome for the future studies of MGTV.
Ticks of Amblyomma testudinarium, D. nuttalli, D. niveus and D. silvarum were captured in our previous studies. Then, the sRNA-seq data from these ticks was produced and deposited in the NCBI SRA (accession numbers SRP084097 and SRP178347; Table 1 "Data" (the first column) was aligned to the reference genome (the 3rd column) to obtain the information on the fourth and fifth columns. "Data" was unique for each run of sRNA-seq data in the NCBI SRA database. The virus strain Yunnan2016 (GenBank: MT080097, MT080098, MT080099 and MT080100) was detected in the present study. The reference genome of the MGTV strain Xinjiang2016 (GenBank: MK174251, MK174244, MK174230 and MK174237) was used to report Yunnan2016. "Coverage" and "Depth" indicated the genome coverage and average depth, respectively (Methods).
Genome coverage and average depth of the MGTV strain Yunnan2016
The y-axis represents the read-counts for each genomic position. A. The x-axis represents positions in the reference genome of the MGTV strain Yunnan2016 (GenBank: MT080097, MT080098, MT080099 and MT080100) and two A. testudinarium ticks were used to produce the sRNA-seq data B. The x-axis represents positions on the reference genome of the MGTV strain Xinjiang2016 (GenBank: MK174251, MK174244, MK174230 and MK174237) and two A. testudinarium ticks were used to produce the sRNAseq data; C. The x-axis represents positions on the reference genome of the MGTV strain Yunnan2016 and three species of ticks (Dermacentor nuttalli, D. niveus and D. silvarum) which were used to produce the sRNA-seq data for our negative controls.
In our previous study, we proposed that 5' and 3' sRNAs can be used to annotate nuclear non-coding and mitochondrial genes at 1-bp resolution, and to identify new steady RNAs, which are usually transcribed from functional genes [9] . In the present study, we used 5' and 3' sRNAs (Figure 2A ) Figure 3A) . Five phylogenetic trees from the 2745-, 2265-, 2427-, 2351-bp and the final CDSs were built. Although these four CDSs had large differences in their degree of evolutionary conservation, the tree topologies were still congruent ( Figure   3BCDEF ). Viruses named as MGTV, JMTV, KDTV and GXTV belong to a MGTV group with two major clades. The two branches oif Clade I had the virus strains isolated from Brazil and Guinea, and the virus strains Yunnan2016 and Xinjiang2016 (Figure 3F) . The Yunnan2016 strain was detected in A.
testudinarium whereas the Xinjiang2016 strain was detected in wild rodents but its biological vector is still unknown. In Clade II (Figure 3F) , the virus strain Kosovo2013 was from humans whereas the strains TT2017-1/-2 were detected in Rhipicephalus (Boophilus) microplus. Viruses closely related to MGTV were primarily associated with patients in Kosovo: two of the three patients had a history of tick bites [16] .
However, the biological vectors of the strains infecting human are still unknown. The Antilles (France) strain was detected in a pool of R. microplus and mblyomma variegatum ticks and the RT-PCR of individual ticks revealed that MGTV existed with a higher prevalence in R. microplus (42%) than A. variegatum (5%) [18] . 
In the present study, we reported a high-quality, fully curated and full-length genome sequence of a new strain of the Mogiana tick virus (MGTV), Yunnan2016. And we show, for the first time, that 5′ and 3′ sRNAs can be used to obtain full-length sequences of the 5' and 3' ends of, but not limited to genome sequences of RNA viruses. And we proved the feasibility of using the sRNA-seq based method for the detection of viruses in a sample containing miniscule RNA.
In total, 17 MGTV strains have been found in five species of ticks: R. microplus (9 virus strains), R. microplus is one of the most widely distributed tick species in the world [19] . R. microplus primarily parasitizes livestock, but it may also feed on people in China. The detection of MGTV in A. testudinarium was reported for the first time in Laos. The nucleotide identity between the genome of the MGTV strain from Laos and the Yunnan2016 genome was 94.73%. Compared to other ticks, the host-range of A.
testudinarium is very large, including mammals, amphibians, reptiles and birds, with widely distributed in tropical and subtropical areas of Asia [20] . The detection of MGTV in wild rodents and humans indicates that the ticks (e.g. R. microplus and A. testudinarium) host MGTV: this hypothesis should be well investigated in future studies.
The full-length genome sequence of the MGTV strain Yunnan2016 has been deposited into NCBI GenBank database under the project accession numbers MT080097, MT080098, MT080099 and MT080100.
In the present study, the 17 MGTV complete genome sequences (including the Yunnan2016) were downloaded from the NCBI GenBank database and analysed together. One genome sequence was removed because it had too many ambiguous nucleotides. The online software CD-HIT [21] (Date: 20191212) was then used to remove redundant sequences, resulting in 9 complete genome sequences for the phylogenetic analysis. The sRNA-seq data used in the present study was also deposited in the NCBI SRA database under the project accession number SRP084097 and SRP178347 ( Table 1) . Using specific primers ( Table 2) , PCR amplification coupled with Sanger sequencing was used to fill the gaps between contigs and to confirm the assembly results. Table 2 . Primers for PCR amplification coupled with Sanger sequencing -10 -"ID" is unique for each Sanger sequence in the present study. RNA1, RNA2, RNA3 and RNA4 of the MGTV strain Yunnan2016 have been submitted to the NCBI GenBank database under the project accession numbers MT080097, MT080098, MT080099 and MT080100, respectively.
The software Fastq_clean [22] was used for sRNA data cleaning and quality control. The virus detection was performed using the pipeline VirusDetect [23] . For each detected virus, VirusDetect assigned a closest reference genome from the NCBI Genbank database to help characterize that virus. VirusDetect used reference genome coverage and average depth to quantify the detected viruses for verification. Genome coverage was defined as the proportion of read-covered positions divided by genome length whereas average depth was the total number of base pairs of aligned reads divided by the read-covered positions of the reference genome. Statistical computation and plotting were performed using the software R v2.15.3
with the Bioconductor packages [24] .