Association of low race performance with mtDNA haplogroup L3b of Australian thoroughbred horses

Mitochondrial DNA (mtDNA) encodes the genes for respiratory chain sub-units that determine the efficiency of oxidative phosphorylation in mitochondria. The aim of this study was to determine if there were any haplogroups and variants in mtDNA that could be associated with athletic performance of Thoroughbred horses. The whole mitochondrial genomes of 53 maternally unrelated Australian Thoroughbred horses were sequenced and an association study was performed with the competition histories of 1123 horses within their maternal lineages. A horse mtDNA phylogenetic tree was constructed based on a total of 195 sequences (including 142 from previous reports). The association analysis showed that the sample groups with poor racing performance history were enriched in haplogroup L3b (p = .0003) and its sub-haplogroup L3b1a (p = .0007), while those that had elite performance appeared to be not significantly associated with haplogroups G2 and L3a1a1a (p > .05). Haplogroup L3b and L3b1a bear two and five specific variants of which variant T1458C (site 345 in 16s rRNA) is the only potential functional variant. Furthermore, secondary reconstruction of 16s RNA showed considerable differences between two types of 16s RNA molecules (with and without T1458C), indicating a potential functional effect. The results suggested that haplogroup L3b, could have a negative association with elite performance. The T1458C mutation harboured in haplogroup L3b could have a functional effect that is related to poor athletic performance.

线粒体DNA（mtDNA）编码呼吸链亚基基因，这些亚基决定线粒体内氧化磷酸化的效率。本研究旨在探究线粒体DNA中是否存在与纯血马（Thoroughbred horses）运动表现相关的单倍群与变异位点。研究对53只母系无关的澳大利亚纯血马的完整线粒体基因组进行测序，并针对1123匹马的母系血统的竞赛历史开展关联分析。基于总计195条序列（其中142条来自既往研究报道）构建了马线粒体DNA系统发育树。关联分析结果显示，竞赛表现不佳的样本组在线粒体单倍群L3b（p=0.0003）及其亚单倍群L3b1a（p=0.0007）中显著富集；而具备顶级竞赛表现的样本组与单倍群G2、L3a1a1a则无显著关联（p>0.05）。单倍群L3b与L3b1a分别携带2个和5个特异性变异位点，其中T1458C变异（对应16S核糖体RNA（16s rRNA）的第345位）是唯一具有潜在功能的变异位点。此外，对16S rRNA的二级结构重构结果显示，携带与不携带T1458C变异的两类16S rRNA分子存在显著结构差异，提示其可能具备功能效应。研究结果表明，单倍群L3b与纯血马的顶级竞赛表现呈负相关。存在于单倍群L3b中的T1458C变异，可能通过发挥功能效应影响马匹的运动表现，进而导致竞赛表现不佳。