Edwardsiella ictaluri (E. ictaluri) is one of the main bacterial pathogens in catfish which has caused serious economic loss to yellow catfish (Pelteobagrus fulvidraco) in China. In our previous work, we demonstrated that CypA was up-regulated at the early stage of E. ictaluri infection in yellow catfish and displayed strong chemotactic activity for leukocytes in vitro. However, the effect of CypA on E. ictaluri is unknown in vivo. Therefore, two homozygous transgenic zebrafish lines expressing yellow catfish CypA (TG-CypA-1 and TG-CypA-2) were generated. After challenged with E. ictaluri at a dose of 1.0 × 10⁴ CFU per adult fish, both two transgenic lines exhibited a higher resistance to bacterial infection than the wildtype zebrafish. Herein, CypA gene in E. ictaluri-challenged yellow catfish was screened for presence of polymorphisms by sequencing and six single nucleotide polymorphisms (SNPs) were identified. SNP association analysis revealed that 528T/C SNP in the first intron was significantly different in disease-susceptible and -resistant groups, which was confirmed in two independent populations of yellow catfish. Moreover, the relative expression of CypA in the resistant group (CC genotype in 528T/C SNP) was significantly higher than that in the susceptible group (TT genotype in 528T/C SNP) in different immune organs of yellow catfish including spleen, head kidney, body kidney and liver. Our results reveal the potential function of CypA in host defense to bacterial infection and suggest the SNP marker in CypA gene associated with the resistance to E. ictaluri may facilitate the selective breeding of disease-resistant yellow catfish in the future.

Edwardsiella ictaluri（E. ictaluri）是鲶鱼的主要病原菌之一，已给我国黄颡鱼（Pelteobagrus fulvidraco）造成严重的经济损失。在我们之前的工作中，我们证明CypA在黄鲶感染E. ictaluri的早期上调，并在体外对白细胞显示出强烈的趋化活性。然而，CypA对E. ictaluri的影响在体内未知。因此，表达黄鲶CypA 的两个纯合转基因斑马鱼品系（TG- CypA -1 和 TG- CypA-2) 生成。在以 每条成年鱼1.0 × 10 ⁴ CFU的剂量用E. ictaluri进行攻击后，两种转基因品系都表现出比野生型斑马鱼更高的细菌感染抵抗力。在此，通过测序筛选了E. ictaluri攻击的黄鲶中的CypA基因是否存在多态性，并鉴定了六个单核苷酸多态性 (SNP)。SNP 关联分析显示，第一个内含子中的 528T/C SNP 在易感组和抗病组中显着不同，这在两个独立的黄鲶鱼种群中得到证实。此外，CypA的相对表达在黄颡鱼脾、头肾、体肾和肝脏等不同免疫器官中，抗性组（528T/C SNP中的CC基因型）显着高于易感组（528T/C SNP中的TT基因型）。我们的研究结果揭示了 CypA 在宿主防御细菌感染中的潜在功能，并表明CypA基因中与E. ictaluri抗性相关的 SNP 标记可能有助于未来抗病黄鲶的选择性育种。