Characterization of the complete mitochondrial genome sequence of Jialuo sheep (Ovis aries).

Jialuo sheep is one of the important production materials of herdsmen in the pastoral areas of northwestern Sichuan in China. We reported the complete mitogenome of Jialuo sheep for the first time. It is 16,617 bp in length, containing 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes, and a control region (D-loop). In the evolutionary relationship, the mitogenome of Jialuo sheep is closer to Texel sheep. This report will help the further studies of sheep species classification and resource protection.

Jialuo sheep is a unique and outstanding new group of grassland Tibetan sheep, mainly distributed in Aba County, Sichuan Province, China (Mou et al. 2012). It has the characteristics of large size, fast growth and development, strong disease resistance, and suitable for grazing in alpine areas (Wu et al. 2009). However, The genetic information of the complete mitogenome used for selection and breeding remains vacant.

In this work, samples were collected Aba Prefecture, Sichuan Province, China (N32°20′, E102°30′). Blood was frozen at –20 °C and stored in the Key Laboratory of Yak Breeding Engineering of Gansu Province. Total genomic DNA was extracted from the blood samples using EasyPure Blood Genomic DNA Kit (Transgen Biotch, Beijing, China) with reference to the manufacturer’s instructions. The complete mitogenome of Jialuo sheep was determined using polymerase chain reaction based on 11 pairs of primers and sequencing (Guo et al. 2005). The sequencing results were assembled using DNASTAR5.0 software (Madison, WI, USA). The complete sequence and annotation were submitted and deposited in GenBank with an accession number MK829158.

The whole mitogenome is a circular DNA molecule of 16,617 bp, consisting of 13 protein-coding genes (ND1-6, ND4L, COX1-3, CYTB, ATP6, and ATP8), 22 transfer RNA genes, 2 ribosomal RNA genes (12s and 16s ribosomal RNA), and a control regain (D-loop) (Hu and Gao 2016). The ratio of basic nucleotide composition is: 33.68% for A, 13.08% for G, 25.83% for C, and 27.38% for T. The G + C base composition (38.91%) was lower than A + T (61.06%). Compared to Texel sheep, the mitogenome of Jialuo sheep has an additional length of 86 bp in the D-loop region

To understand the genetic relationship between Jaluo and other cultivars, we constructed a phylogenetic tree based on the mitochondrial genome of six species using MEGA 7.0 software with the neighbor-joining (NJ) method of 1000 bootstrap replicates (Kumar et al. 2016). The result shows that Jialuo sheep is closer to Texel sheep in mitogenome evolution (Figure 1). The sequence and annotation provided in this work will contribute to sheep classification and protection of genetic resource.

Figure 1.

Phylogenetic tree based on the mitochondrial genome of six species using the neighbor-joining (NJ) method of 1000 bootstrap replicates.