YTH domain-containing genes are important readers of N⁶-methyladenosine (m⁶A) modifications with ability to directly affect the fates of distinct RNAs in organisms. Despite their importance, little is known about YTH domain-containing genes in teleosts until now. In the present study, a total of 10 YTH domain-containing genes have been systematically identified and functionally characterized in rainbow trout (Oncorhynchus mykiss). According to the phylogenetic tree, gene structure and syntenic analysis, these YTH domain-containing genes could be classified into three evolutionary subclades, including YTHDF, YTHDC1 and YTHDC2. Of them, the copy number of OmDF1, OmDF2, OmDF3, and OmDC1 were duplicated or even triplicated in rainbow trout due to the salmonid-specific whole-genome duplication event. The three-dimensional protein structure analysis revealed that there were similar structures and the same amino acid residues that were associated with cage formation between humans and rainbow trout, implying their similar manners in binding to m⁶A modification. Additionally, the results of qPCR experiment indicated that the expression patterns of a few YTH domain-containing genes, especially OmDF1b, OmDF3a and OmDF3b, were significantly different in liver tissue of rainbow trout under four different temperatures (7 °C, 11 °C, 15 °C, and 19 °C). The expression levels of OmDF1a, OmDF1b and OmDC1a were obviously repressed in spleen tissue of rainbow trout at 24 h after Yersinia ruckeri infection, while increased expression was detected in OmDF3b. This study provides a systemic overview of YTH domain-containing genes in rainbow trout and reveals their biological roles in responses to temperature stress and bacterial infection.

Gene presence/absence variations (PAVs) have been considered as the important determinants of genome evolution and phenotypic diversity. However, studies on gene PAVs have been poorly documented, especially in fishes. In the present study, the pan-genome of rainbow trout was constructed based on 268 whole-genome re-sequencing accessions (4.38 Tb data). It recovered an additional 62 Mb sequences and 1288 protein-coding genes. Then, 9831 (22.77%) gene PAVs were genotyped across the 268 individuals. PAV-based PCA analysis, together with phylogenetic topology and STRUCTURE, revealed the clear separation among the different wild and selection populations. Additionally, a PAV-based genome-wide association study (GWAS) identified three candidate PAVs significantly associated with artificial selection. Meanwhile, fixation index analysis revealed 35 PAVs with significant frequency differences between wild and selection populations in Canada, while 15 candidate PAVs were detected between the populations in America. Their biological functions have been reported to participate in the regulation of growth performance and stress response. The present study deepens our understanding of widespread gene PAVs and facilitates the identification of key candidates that contribute to important traits.