Molluscan shell is a biomineral that consists of a highly organized calcium carbonate composite.Organisms mainly use matrix proteins to elaborately control the biomineralization process,but knowledge of their regulatory mechanisms is limited.The transcription factor Pf-Rel,which belongs to the Rel/nuclear factor-κB family,was shown to regulate transcription at the Nacrein promoter in the pearl oyster Pinctada fucata.Here,we further explored the transcriptional regulation mechanisms of Pf-Rel on the matrix proteins Prismalin-14 and MSI60.The relative expression levels of Prismalin-14 and MSI60 were high in the mantle edge and mantle pallial tissues of P.fucata.These three genes were significantly up-regulated after shell notching,suggesting that they might play important roles during shell formation.Importantly,Pf-Rel gene knockdown by RNA interference led to down-regulation of Prismalin-14 and MSI60 expression.In transient co-transfection assays,Pf-Rel significantly up-regulated the promoter activities of the Prismalin-14 and MSI60 genes in a dose-dependent manner.Furthermore,the promoter regions of Prismalin-14 (-1794 to-1599 bp) and MSI60 (-2244 to-1141 bp) were required for the activation by Pf-Rel.Altogether,these results suggest that the transcription factor Pf-Rel can up-regulate the expression of the matrix protein genes Prismalin-14 and MSI60 during shell formation in P.fucata,which improves our understanding of transcription regulation at the molecular level during molluscan shell development.