Characterization of DDX21 gene and the association of its single nucleotide polymorphisms with susceptibility/resistance of Magallana gigas to Halomonas sp. 7T

DEAD-box RNA helicase 21 (DDX21) is a widely expressed protein in cells, involved in almost all RNA-related cellular processes, and plays a significant role in disease prevention and defense within organisms. This study characterized a DDX21 in Pacific oyster Magallana gigas (MgDDX21), and investigated its association of single nucleotide polymorphisms with susceptibility/resistance of oyster to Halomonas sp. 7T. MgDDX21 contains three conserved domains (DEADc, HELICc, and GUCT), and shares highly conserved key functional sites with other organisms. High-temperature and Lipopolysaccharide (LPS) treatment both significantly upregulated the mRNA expression level of MgDDX21 (P < 0.05). The promoter sequence of MgDDX21 gene from the bacterial-resistant population and the common population was cloned, and the polymorphisms within this region were investigated by sequencing to analyze their association with bacterial resistance. A total of 25 single nucleotide polymorphism (SNP) sites were identified, and 21 SNPs and one haplotype TACACTAACT were significantly associated with the bacterial resistance trait of Pacific oyster, which could be used as potential markers for oyster selection breeding with higher bacterial resistance. These results lay the foundation for further investigation into the role of DDX21 in the response of Pacific oyster to bacterial resistance and provide candidate molecular markers for breeding new varieties of oysters with excellent disease resistance traits.