Abstract: Matrix metalloproteinases(MMPs)could degrade the extracellular matrix and participate in various physiological processes,such as homeostasis and immune response.MMP-17 is one membrane type MMP that attaches to the cell surface by Glycosyl-phosphatidyl inositol(GPI),and participates in various physiological processes,such as organic homeostasis and immune defense.The pearl oyster Pinctada martensii is the main species cultured for marine pearl production in China.To deliberate the function of MMP-17 in the immune response of P.martensii,in this study,using rapid amplification of cDNA ends(RACE)technology,we have obtained the full length sequence of Pinctada martensii MMP(Pm-MMP-17)cDNA and analyzed its sequence characteristics and function.Our results showed that the cDNA full length of Pm-MMP-17 is 2 794 bp,including 156 bp of 5'UTR,715 bp of 3'UTR,and 1 923 bp of open reading frame(ORF)encoding 640 amino acid residues with an estimated molecular mass of 73.11 ku and theoretical isoelectric point of 8.98.Multi-sequence alignment and phylogenetic analysis results showed that Pm-MMP-17 was highly homologous with that from other species and had 82% sequence identity with Crassostrea gigas MMP-17.Amino acid sequence analysis showed Pm-MMP-17 had five conservative domains:signal peptide,propeptide,catalytic domain,hinge region and hemopexin-like domain.Meanwhile,real-time PCR analysis showed that Pm-MMP-17 was ubiquitously expressed in all tissues detected,including adductor muscle,pearl sac,foot,mantle,hemolymph,hepatopancreas,gonads and gills,with the highest expression level in hemolymph,followed by adductor muscle and gill.Previous research has showed that Pm-MMP-17 was highly expressed in the eosinophils and involved in the regulation of cell migration,growth and differentiation.We supposed that the highly expression of Pm-MMP-17 gene in the hemolymph was crucial for the migration of hemolymph in the body of pearl oyster.After LPS stimulation,the expression level of Pm-MMP-17 began to increase and reached the highest level at 12 h,and then gradually declined to the normal level(P<0.05),indicating again the important function of Pm-MMP-17 gene in the immune response of pearl oyser P.martensii.Therefore,our data showed Pm-MMP-17 participated in the immune response in P.martensii and provided the basis for further research in the mechanism underlying the immune defense in pearl oyster.