A new anti-lipopolysaccharide factor (ALF) gene with its SNP polymorphisms related to WSSV-resistance of Litopenaeus vannamei.

Anti-lipopolysaccharide factors (ALFs) of crustacean play an important role against bacteria or virus infection. In this study, the cDNA sequence and genomic sequence of one new isoform of ALF designated as nLvALF1 were reported. The open reading frame (ORF) of nLvALF1 consisted of 369 bp encoding 123 amino acids and the genomic structure of nLvALF1 comprised four introns and three exons. The predicted pI of the deduced protein was 8.82 and the molecular weight (MW) was 13.72 KDa. The deduced amino acid sequence of nLvALF1 contained a typical functional domain of ALF: LPS-binding domain. Phylogenetic analysis showed that nLvALF1 had the closest relationship with FcALF1 from Fenneropenaeus chinensis. The nLvALF1 was specifically expressed in lymphoid organ (Oka) of shrimp. Its transcriptional level was significantly up-regulated after white spot syndrome virus (WSSV) challenge, suggesting that nLvALF1 might participate in defense against WSSV in Litopenaeus vannamei. In order to search potential genetic markers associated with WSSV-resistance, we scanned the polymorphisms of the genomic fragment with 397 bp where the LPS-binding domain encoding sequence located and 18 SNPs were found. The distribution frequency of these SNPs was analyzed in WSSV susceptible shrimp and resistant shrimp separately. Significant differences existed in allelic frequencies at loci g.1361-T > C, g.1370-T > C, g.1419-T > A between the WSSV-resistant group and the WSSV-susceptible/susceptible group (P < 0.05). The specific haplotype CT consisted of g.1415-C > A and g.1419-T > A was associated with susceptibility to WSSV (P < 0.05). These findings provide theoretical support for selection of WSSV-resistant varieties of L. vannamei.