Papers of the Week

Maize yellow mosaic virus (MaYMV), a new species in the genus (family ), was reported in maize for the first time in China in 2016 (Chen et al., 2016). Later, MaYMV was found in other gramineous species including sugarcane ( spp.), itch grass (), millet () and sorghum () in several countries in Asia, Africa, and South America (Yahaya et al. 2017; Lim et al. 2018; Sun et al. 2019; Nithya et al. 2021). Here, we report its presence in cultivated wheat (), detected using high-throughput sequencing (HTS). In 2021 in Henan Province, China, wheat plants with virus-like symptoms such as yellowing, stunting, and vein clearing were collected from fields in Luoyang (three plants, cv. Luohan 6), Nanyang (two plants, cv. Xinong 979), and Anyang (one plant, cv. Bainong 207). RNA was extracted from symptomatic leaves of each plant sample using TRIzol reagent (Invitrogen, Carlsbad, CA, USA). From each sample, 1 μg of RNA was mixed into a single pool to construct an rRNA-depleted RNA-seq library using a TruSeq RNA Sample Prep Kit for sequencing on the HiSeq X-Ten platform as 150-bp paired-end reads. A total of 88,892,804 clean reads were obtained after removing adaptor sequences and low-quality reads. Reads were mapped against the wheat genome database (IWGSC RefSeq v2.1) using the hisat2 v2.0.5 program. Remaining sequences were de novo assembled into contigs with Trinity program. Contigs from barley yellow dwarf virus PAV (BYDV-PAV), and BYDV-GAV were identified using a Blast search of the NCBI nr/nt database, all previously reported in wheat in China. Interestingly, four contigs with high similarity (>95%, at the nucleotide level) to MaYMV were also identified. Using the sequence of MaYMV isolate Yunnan 9 (KU291105) as reference, a total of 1,260 reads from HTS mapped to the virus genome with a coverage of 75.5% (average coverage: 33.5×). For verifying the presence of MaYMV in the source samples, MaYMV-specific primers MV-fw/MV-rev were designed to amplify the 513-bp fragment of the RdRp gene by a reverse transcription-polymerase chain reaction (RT-PCR) using the original total RNA. RT-PCR assay revealed that only 1 of the 6 samples tested positive for MaYMV, while the remaining plants were positive for other viruses (BYDV-PAV and BYDV-GAV that produce similar symptoms; viral-specific primers as previously described [Liu et al., 2020]). A subsequent survey of 17 winter wheat fields in 2021 confirmed that 6 of 286 wheat samples with virus symptoms were infected with MaYMV; 4 positives were from Linfen, Shanxi Province and 1 each from Yuanyang and Anyang, Henan Province. The full genome of wheat-infecting MaYMV isolate Anyang1 was then sequenced using RT-PCR with Sanger sequencing technology; the genomic sequence (5,642 nt) was deposited in GenBank as accession OK331995. BLASTn search showed that the complete genome sequence of this virus is 99.0%, 98.9% and 98.7% identical to isolate SC1 (MK652148), Guizhou1 (KU291107) and Yunnan 11 (KU248489), respectively. Also, the MaYMV isolate Anyang1 obtained in this study clustered with other MaYMV isolates in a phylogenetic analysis based on MaYMV full genomes. To the best of our knowledge, this is the first report of MaYMV in wheat worldwide. The presence of MaYMV in wheat is important because winter wheat could serve as an overwintering reservoir of MaYMV and perpetuate the virus in wheat-maize rotation systems in northern China.