Glycogen, a stored form of glucose, is an important form of energy for aquatic shellfish, contributing to the flavor and quality of the oyster. The glycogen synthase (GYS) and glycogen synthase kinase 3β (GSK3β) are two major enzymes in the glycogenesis. However, the information of the two genes in the Jinjiang oyster Crassostrea ariakensis remains limited. In this study, we identified the genes of GYS and GSK3β and further explored their function in the glycogen synthesis of C. ariakensis. The GYS and GSK3β were distributed in all tested tissues, and high expression of GYS and glycogen content were detected in the gonad, labial palp, hepatopancreas, and mantle, while the high expression of GSK3β was observed in the gill and adductor muscle. The expression of GYS was positively correlated with the glycogen content, while GSK3β was negatively correlated. Additionally, knockdown of GSK3β using RNAi decreased the GYS expression, revealing the negative regulatory effect of GSK3β on GYS. These findings enrich the research data of GSK3β and GYS involved in glycogen synthesis, providing valuable information for further research on the function of GSK3β and GYS in the glycogen synthesis process of oyster.

Bivalve mollusks, comprising animals enclosed in two shell valves, are well-adapted to benthic life in many intertidal zones. Clams have evolved the buried lifestyle, which depends on their unique soft tissue structure and their wedge-shaped muscular foot and long extendible siphons. However, molecular mechanisms of adaptative phenotype evolution remain largely unknown. In the present study, we obtain the high-quality chromosome-level genome of Manila clam R. philippinarum, an economically important marine bivalve in many coastal areas. The genome is constructed by the Hi-C assisted assembly, which yields 19 chromosomes with a total of 1.17 Gb and BUSCO integrity of 92.23%. The de novo assembled genome has a contig N50 length of 307.7 kb and scaffold N50 of 59.5 Mb. Gene family expansion analysis reveals that a total of 24 single-copy gene families have undergone the significant expansion or contraction, including E3 ubiquitin ligase and dynein heavy chain. The significant expansion of transposable elements has been also identified, including long terminal repeats (LTR) and non-LTR retrotransposons. The comparative transcriptomics among different clam tissues reveals that extracellular matrix (ECM) receptors and neuroactive ligand receptors may play the important roles in tissue structural support and neurotransmission during their infaunal life. These findings of gene family expansion and tissue-specific expression may reflect the unique soft tissue structure of clams, suggesting the evolution of lineage-specific morphological novelties. The high-quality genome and transcriptome data of R. philippinarum will not only facilitate the genetic studies on clams but will also provide valuable information on morphological novelties in mollusks.