RNAi Identified the Potential Functions of Actin-like Protein in the Growth Performance of Macrobrachium nipponense

<i>Macrobrachium nipponense</i> is an important commercial freshwater prawn species in China. Since larger individuals command higher market value, there is a pressing need to identify growth-related genes and single-nucleotide polymorphisms (SNPs) to facilitate genetic improvement in this species. Previous studies have suggested a potentially regulatory role of an actin-like protein (<i>ACTL</i>) in the growth of <i>M. nipponense</i>. Therefore, the present study aimed to functionally characterize the role of <i>ACTL</i> in growth and identify growth-associated SNPs within this gene. The open reading frame of <i>Mn-ACTL</i> is 1131 bp, encoding a protein with 377 amino acids. Blastx and phylogenetic analyses indicated that <i>Mn-ACTL</i> shares a close evolutionary relationship with orthologs from <i>Macrobrachium rosenbergii</i> and <i>Palaemon carinicauda</i>. The highest expression level of <i>Mn-ACTL</i> in muscle tissue detected by qPCR suggested its potential involvement in growth regulation. RNA interference experiments showed that prawns injected with <i>dsGFP</i> exhibited larger body sizes than those injected with <i>dsACTL</i>, indicating that knockdown of <i>Mn-ACTL</i> expression inhibits growth performance in <i>M. nipponense</i>. Furthermore, muscle tissue from the <i>dsACTL</i>-injected group displayed looser myofibril packing, visibly eroded areas, and increased sarcomere spacing. Collectively, these results demonstrated that <i>ACTL</i> positively regulates growth in <i>M. nipponense</i>. Additionally, the T allele at locus S28_17149891 and the G allele at locus S28_17145758 were significantly associated with growth traits (<i>p</i> < 0.05). In conclusion, this study confirmed the positive regulatory role of <i>ACTL</i> in growth and identified growth-associated SNPs in <i>M. nipponense</i>, providing valuable insights for breeding new varieties with enhanced growth performance in this species.