GABI, INRA, AgroParisTech, Université Paris-Saclay, 78350, Jouy-en-Josas, France.
SYSAAF Section Aquacole, Campus de Beaulieu, 35000, Rennes, France.
Genet Sel Evol. 2018 Nov 16;50(1):60. doi: 10.1186/s12711-018-0431-9.
Bacterial cold-water disease, which is caused by Flavobacterium psychrophilum, is one of the major diseases that affect rainbow trout (Oncorhynchus mykiss) and a primary concern for trout farming. Better knowledge of the genetic basis of resistance to F. psychrophilum would help to implement this trait in selection schemes and to investigate the immune mechanisms associated with resistance. Various studies have revealed that skin and mucus may contribute to response to infection. However, previous quantitative trait loci (QTL) studies were conducted by using injection as the route of infection. Immersion challenge, which is assumed to mimic natural infection by F. psychrophilum more closely, may reveal different defence mechanisms.
Two isogenic lines of rainbow trout with contrasting susceptibilities to F. psychrophilum were crossed to produce doubled haploid F2 progeny. Fish were infected with F. psychrophilum either by intramuscular injection (115 individuals) or by immersion (195 individuals), and genotyped for 9654 markers using RAD-sequencing. Fifteen QTL associated with resistance traits were detected and only three QTL were common between the injection and immersion. Using a model that accounted for epistatic interactions between QTL, two main types of interactions were revealed. A "compensation-like" effect was detected between several pairs of QTL for the two modes of infection. An "enhancing-like" interaction effect was detected between four pairs of QTL. Integration of the QTL results with results of a previous transcriptomic analysis of response to F. psychrophilum infection resulted in a list of potential candidate immune genes that belong to four relevant functional categories (bacterial sensors, effectors of antibacterial immunity, inflammatory factors and interferon-stimulated genes).
These results provide new insights into the genetic determinism of rainbow trout resistance to F. psychrophilum and confirm that some QTL with large effects are involved in this trait. For the first time, the role of epistatic interactions between resistance-associated QTL was evidenced. We found that the infection protocol used had an effect on the modulation of defence mechanisms and also identified relevant immune functional candidate genes.
由嗜冷杆菌引起的细菌性冷水病是影响虹鳟（Oncorhynchus mykiss）的主要疾病之一，也是养殖鳜鱼的主要关注点。更好地了解对嗜冷杆菌的遗传抗性基础将有助于在选择方案中实施这一特性，并研究与抗性相关的免疫机制。多项研究表明，皮肤和黏液可能有助于对感染的反应。然而，之前的数量性状基因座（QTL）研究是通过注射作为感染途径进行的。浸泡挑战更能模拟嗜冷杆菌的自然感染，可能会揭示不同的防御机制。
用具有不同对嗜冷杆菌易感性的两个虹鳟近交系杂交产生了双单倍体 F2 后代。鱼用嗜冷杆菌肌肉内注射（115 条）或浸泡（195 条）感染，并使用 RAD 测序对 9654 个标记进行了基因型分析。检测到 15 个与抗性性状相关的 QTL，只有 3 个 QTL 在注射和浸泡之间是共同的。使用一种考虑 QTL 之间上位性相互作用的模型，揭示了两种主要的相互作用类型。在两种感染方式中，检测到几对 QTL 之间存在“补偿样”效应。在四对 QTL 之间检测到“增强样”相互作用效应。将 QTL 结果与先前对嗜冷杆菌感染反应的转录组分析结果整合在一起，得到了一组可能属于四个相关功能类别（细菌传感器、抗菌免疫效应物、炎症因子和干扰素刺激基因）的潜在候选免疫基因。
这些结果为虹鳟对嗜冷杆菌的遗传抗性的遗传决定因素提供了新的见解，并证实了一些具有较大效应的 QTL 参与了这一性状。首次证明了与抗性相关的 QTL 之间的上位性相互作用的作用。我们发现，使用的感染方案会影响防御机制的调节，还确定了相关的免疫功能候选基因。
