The polymorphism of lysozyme gene in Zhikong scallop ( Chlamys farreri) and its association with susceptibility/resistance to Listonella anguillarum

Abstract

Lysozyme functions as a crucial biodefence effector against the infection of bacterial pathogens in innate immunity. The nucleotide sequence polymorphisms in promoter region of a nuclear goose type lysozyme gene from Zhikong scallop Chlamys farreri (designated as CFLysG) were investigated to explore their association with susceptibility/resistance to Listonella anguillarum infection. Eight sites of single nucleotide polymorphisms (SNPs) and two sites of insert-deletion (ins-del) polymorphisms were identified in the promoter region of CFLysG. Two of them, −753 TATCTCGATCAGG ins-del polymorphism and −391 A–G SNP were selected to analyze their distribution in the susceptible and resistant stocks, which were identified according to the survival time after L. anguillarum challenge. Using polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP), two genotypes were found at each site, which were ins/del and ins/ins at locus −753, and A/A and A/G at locus −391, respectively. The −753 ins/del genotype was more prevalent in the resistant stock than that in the susceptible stock, 30% vs 16.67% in frequency, but there was no significant difference in the frequency distribution between these two stocks ( P = 0.15). In contrast, the frequency of −391A/G genotype in the resistant stock was significantly higher (30%) than that in the susceptible stock (7.14%) ( P = 0.007), indicating a significant association with the resistance of Zhikong scallop to L. anguillarum. To confirm the presumption, another independent challenge experiment was performed, in which the cumulative mortality of scallops with −391 A/A genotype (96.8%) was significantly higher than those with −391 A/G genotype (64.5%) ( P = 0.001), which further validate the association between −391 A/G genotype and the resistance of Zhikong scallop to L. anguillarum. These results suggested that the −391 A/G could be a potential marker applied in future selection of Zhikong scallop with enhanced resistance to L. anguillarum.