High polymorphism in big defensin gene expression reveals presence-absence gene variability (PAV) in the oyster Crassostrea gigas

• Published in: Developmental & Comparative Immunology
• Main Authors: Rosa, Rafael D., Alonso, Pascal, Santini, Adrien, Vergnes, Agnes, Bachere, Evelyne
• Format: Text
• Language: English
• Published: Elsevier
• Subjects: envir; archeo; Crassostrea gigas
• Online Access: https://doi.org/10.1016/j.dci.2014.12.002; https://archimer.ifremer.fr/doc/00239/35009/33545.pdf; https://archimer.ifremer.fr/doc/00239/35009/

We report here the first evidence in an invertebrate, the oyster Crassostrea gigas, of a phenomenon of Presence-Absence Variation (PAV) affecting immune-related genes. We previously evidenced an extraordinary interindividual variability in the basal mRNA abundances of oyster immune genes including those coding for a family of antimicrobial peptides, the big defensins (Cg-BigDef). Cg-BigDef is a diverse family composed of three members: Cg-BigDef1 to -3. Here, we show that besides a high polymorphism in Cg-BigDef mRNA expression, not all individual oysters express simultaneously the three Cg-BigDefs. Moreover, in numerous individuals, no expression of Cg-BigDefs could be detected. Further investigation at the genomic level revealed that in individuals in which the transcription of one or all Cg-BigDefs was absent the corresponding Cg-bigdef gene was missing. In our experiments, no correlation was found between Cg-bigdef PAV and oyster capacity to survive Vibrio infections. The discovery of P-A immune genes in oysters leads to reconsider the role that plays the immune system in the individual adaptation to survive environmental, biotic and abiotic stresses.