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The giant freshwater prawn Macrobrachium rosenbergii distributed from tropical to subtropical regions, is a warm-water species, and its survival temperature is 14–35 °C, which greatly limits its culture cycle and culture area in China. Therefore, it is urgent to cultivate a new high quality, high yield variety with improved cold-resistance, but the genetic parameters for cold-resistance traits are unknown in M. rosenbergii. In this study, the cold-resistance of adult M. rosenbergii populations was tested using the indoor artificial cooling method. Individuals were selected from 139 families of Shufeng G3 generation and cultured for 200 days. A linear mixed model was constructed by ASReml-R to evaluate the genetic parameters of the cold-resistance trait (cooling degree hours, CDH) and growth traits (body weight, BW, and body length, BL) based on the restricted maximum likelihood (REML) method. The results show that the heritability of CDH was low (0.12±0.05), while the growth traits (BW and BL) had low to moderate heritability, with 0.20±0.06 for BW and 0.06±0.04 for BL. The phenotypic and genetic correlation between BW and BL was significantly positive, but significantly negative phenotypic and genetic correlations were detected between CDH and BW and between CDH and BL. Furthermore, the analysis of the differences between cold-resistance and phenotypic traits showed that the female reproductive status, exoskeleton hardness and claw number of adult prawns had a great influence on the cold-resistance of M. rosenbergii (P<0.05), indicating that adults with claws and hard exoskeletons are preferred as parents in subsequent breeding selection. The present results can be attributed to the selection and breeding of a new cold-resistant variety of M. rosenbergii. [ABSTRACT FROM AUTHOR]

Myeloid differentiation factor 88 (MyD88) is a crucial adaptor protein for Toll-like receptor (TLR)-mediated signaling pathways and plays an important role in immune response. In this study, the full-length cDNA of MyD88 from Macrobrachium rosenbergii (MRMyD88) was cloned. The MRMyD88 cDNA is 1758 bp long and contains a 1398-bp open reading frame. Multiple sequence alignment and phylogenetic analysis revealed that the amino acid sequence of MRMyD88 shared high identity with the known MyD88 proteins. The MRMyD88 mRNA was widely expressed in all examined tissues, with highest level in intestine, followed by gonad and pleopod. Furthermore, the MRMyD88 promoter region, spanning 1622 bp, contains several transcription factor-binding sites, including nine GATA-1 box motifs. Electrophoretic mobility shift assay showed that Gfi-1, SRF, and Oct-1 bind to the upstream region of MRMyD88. Additionally, the results showed that the expression levels of TLR1 , TLR2 and TLR3 were different in response to Vibrio anguillarum , Lactobacillus plantarum and Aeromonas hydrophila infections. However, these bacteria significantly increased the expression levels of MyD88 and prophenoloxidase. These data suggest that the TLR -mediated signaling pathway is MyD88 -dependent in response to pathogenic and probiotic bacteria in M. rosenbergii. [ABSTRACT FROM AUTHOR]

Vibrio anguillarum is a globally distributed aquatic pathogen, and its flagellin B (FlaB) protein can evoke innate immune responses in hosts. In order to explore the role of FlaB in V. anguillarum infection, we constructed a FlaB-deficient mutant using overlapping PCR and two-step homologous recombination, and gene sequencing confirmed successful knockout of the FlaB gene. Scanning electron microscopy showed no significant differences in the morphological structure of the flagellum between wild-type and FlaB-deficient strains. The mutant was subsequently injected into the freshwater prawn (Macrobrachium rosenbergii) to explore its pathogenicity in the host, and expression of myeloid differentiation factor 88, prophenoloxidase, catalase, superoxide dismutase and glutathione peroxidase was investigated by real-time PCR. The results showed that deletion of FlaB had little effect on V. anguillarum -induced expression of these immune-related genes (p > 0.05). In general, the FlaB mutant displayed similar flagella morphology and immune characteristics to the wild-type strain, hence we speculated that knockout of FlaB might promote the expression and function of other flagellin proteins. Furthermore, this study provides a rapid and simple method for obtaining stable mutants of V. anguillarum free from foreign plasmid DNA. [ABSTRACT FROM AUTHOR]