Caractérisation de marqueurs génétiques fonctionnels de la nutrition et/ou de l'adaptation (les amylases) chez l'huître creuse Crassostrea gigas : intérêts pour la sélection

Two amylase genes, A and B, from the oyster Crassostrea gigas were characterized. Using PCR-RFLP, 6 and 4 alleles, respectively, were described for the amylase genes A and B. The roles of A and B amylase genes were investigated experimentally. They are expressed during larval and adult stages, and A transcripts are more abundant than B. The A transcript increases significantly with temperature, in high trophic conditions. However, A and B transcript levels do not change when food quantity increases although amylase activity augments. The level of B is correlated with dietary starch quantities, whereas the amount of A appears to remain constant ; simultaneously amylase activity decreases and the KM increases. These results suggest that expression of B is regulated by diet quality in contrast to A expression. And that the B amylase probably has a higher KM. In order to study the relationships between polymorphism and amylase function, 5 bi-parental families with checked polymorphisms were bred and reared in two geographic areas over one year. Significant growth differences between genotypes of a same family were mainly observed in one location, indicative for a site effect. Some genotypes, displaying significant differences in growth, demonstrated variations in amylase activity although their KM remained constant. Survival performance was not influenced by these amylase polymorphisms. This correlation between amylase polymorphism and growth indicates that growth of C. gigas oysters can be improved using the amylase markers for selective breeding programs.