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

Rosa, R.D., Alonso, P., Santini, A. et al.

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 the immune system plays in the individual adaptation to survive environmental, biotic and abiotic stresses.

Citation

Rosa, R.D., Alonso, P., Santini, A. et al. "High polymorphism in big defensin gene expression reveals presence-absence gene variability (PAV) in the oyster Crassostrea gigas" Developmental and Comparative Immunology (2015): 231–8