Development of a SNP linkage map and genome-wide association study for resistance to Aeromonas hydrophila in pacu (Piaractus mesopotamicus).

BACKGROUND: Pacu (Piaractus mesopotamicus) is one of the most important Neotropical aquaculture species from South America. Disease outbreaks caused by Aeromonas hydrophila infection have been considered significant contributors to the declining levels of pacu production. The current implementation of genomic selection for disease resistance has been adopted as a powerful strategy for improvement in fish species. This study aimed to investigate the genetic architecture of resistance to A. hydrophila in pacu via Genome-Wide Association Study (GWAS), the identification of suggestive Quantitative Trait Loci (QTLs) and putative genes associated with this trait. The genetic data were obtained from 381 juvenile individuals belonging to 14 full-sibling families. An experimental challenge was performed to gain access to the levels of genetic variation for resistance against the bacteria using the following trait definitions: binary test survival (TS) and time of death (TD). RESULTS: The analyses of genetic parameters estimated moderate heritability (h2) for both resistance traits: 0.20 (± 0.09) for TS and 0.35 (± 0.15) for TD. A linkage map for pacu was developed to enable the GWAS, resulting in 27 linkage groups (LGs) with 17,453 mapped Single Nucleotide Polymorphisms (SNPs). The length of the LGs varied from 79.95 (LG14) to 137.01 (LG1) cM, with a total map length of 2755.60 cM. GWAS identified 22 putative QTLs associated to A. hydrophila resistance. They were distributed into 17 LGs, and were considered suggestive genomic regions explaining > 1% of the additive genetic variance (AGV) for the trait. Several candidate genes related to immune response were located close to the suggestive QTLs, such as tbk1, trim16, Il12rb2 and lyz2. CONCLUSION: This study describes the development of the first medium density linkage map for pacu, which will be used as a framework to study relevant traits to the production of this species. In addition, the resistance to A. hydrophila was found to be moderately heritable but with a polygenic architecture suggesting that genomic selection, instead of marker assisted selection, might be useful for efficiently improving resistance to one of the most problematic diseases that affects the South American aquaculture.

Molecular characterization and gene expression of ferritin in red abalone (Haliotis rufescens).

Ferritin is the principal iron storage protein in the majority of living organisms. Its capacity to capture the toxic cellular iron in excess in a compact and safe manner, gives to this protein a key role in detoxification and iron storage. It has a main role in cellular homeostasis and in cellular defense against oxidative stress produced by the reactive oxygen species (ROS). In this research, the cDNA coding sequence of ferritin for Red abalone (Haliotis rufescens) was obtained, which had an open reading frame (ORF) of 516 bp. The deduced amino acid sequence was consisted of 171 residues with a calculated molecular weight of 19.77 kDa. In addition, tissue expression profiles of ferritin in Red abalone were induced by thermal stress showed an expression peak from 16 °C to 22 °C. The transcriptional level of ferritin was mainly achieved in muscle, digestive gland, gills, foot, mantle and gonad respectively. This research providing more information to better understands the structural and functional properties of this protein in Haliotis.