The polymorphism in the promoter region of metallothionein 1 is associated with heat tolerance of scallop Argopecten irradians.

Metallothioneins (MTs), a superfamily of cysteine-rich proteins, perform multiple functions, such as maintaining homeostasis of essential metals, detoxification of toxic metals and scavenging of oxyradicals. In this study, the promoter region of a metallothionein (MT) gene from Bay scallop Argopecten irradians (designed as AiMT1) was cloned by the technique of genomic DNA walking, and the polymorphisms in this region were screened to find their association with susceptibility or tolerance to high temperature stress. One insert-deletion (ins-del) polymorphism and sixteen single nucleotide polymorphisms (SNPs) were identified in the amplified promoter region. Two SNPs, -375 T-C and -337 A-C, were selected to analyze their distribution in the two Bay scallop populations collected from southern and northern China coast, which were identified as heat resistant and heat susceptible stocks, respectively. There were three genotypes, T/T, T/C and C/C, at locus -375, and their frequencies were 25%, 61.1% and 13.9% in the heat susceptible stock, while 34.2%, 42.1% and 23.7% in the resistant stock, respectively. There was no significant difference in the frequency distribution of different genotypes between the two stocks (P>0.05). In contrast, at locus -337, three genotypes A/A, A/C and C/C were revealed with the frequencies of 11.6%, 34.9% and 53.5% in the heat susceptible stock, while 45.7%, 32.6% and 21.7% in the heat resistant stock, respectively. The frequency of C/C genotype in the heat susceptible stock was significantly higher (P<0.01) than that in the heat resistant stock, while the frequency of A/A in the heat resistant stock was significantly higher (P<0.01) than that in the heat susceptible stock. Furthermore, the expression of AiMT1 mRNA in scallops with C/C genotype was significantly higher than that with A/A genotype (P<0.05) after an acute heat treatment at 28°C for 120min. These results implied that the polymorphism at locus -337 of AiMT1 was associated with the susceptibility/tolerance of scallops to heat stress, and the -337 A/A genotype could be a potential marker available in future selection of Bay scallop with heat tolerance.