The mosaic genome of indigenous African cattle as a unique genetic resource for African pastoralism.

Cattle pastoralism plays a central role in human livelihood in Africa. However, the genetic history of its success remains unknown. Here, through whole-genome sequence analysis of 172 indigenous African cattle from 16 breeds representative of the main cattle groups, we identify a major taurine × indicine cattle admixture event dated to circa 750-1,050 yr ago, which has shaped the genome of today's cattle in the Horn of Africa. We identify 16 loci linked to African environmental adaptations across crossbred animals showing an excess of taurine or indicine ancestry. These include immune-, heat-tolerance- and reproduction-related genes. Moreover, we identify one highly divergent locus in African taurine cattle, which is putatively linked to trypanotolerance and present in crossbred cattle living in trypanosomosis-infested areas. Our findings indicate that a combination of past taurine and recent indicine admixture-derived genetic resources is at the root of the present success of African pastoralism.

Transcriptome Analysis of Diurnal Gene Expression in Chinese Cabbage.

Plants have developed timing mechanisms that enable them to maintain synchrony with daily environmental events. These timing mechanisms, i.e., circadian clocks, include transcriptional/translational feedback loops that drive 24 h transcriptional rhythms, which underlie oscillations in protein abundance, thus mediating circadian rhythms of behavior, physiology, and metabolism. Circadian clock genes have been investigated in the diploid model plant Arabidopsis thaliana. Crop plants with polyploid genomes-such as Brassica species-have multiple copies of some clock-related genes. Over the last decade, numerous studies have been aimed at identifying and understanding the function of paralogous genes with conserved sequences, or those that diverged during evolution. Brassicarapa's triplicate genomes retain sequence-level collinearity with Arabidopsis. In this study, we used RNA sequencing (RNAseq) to profile the diurnal transcriptome of Brassicarapa seedlings. We identified candidate paralogs of circadian clock-related genes and assessed their expression levels. These genes and their related traits that modulate the diurnal rhythm of gene expression contribute to the adaptation of crop cultivars. Our findings will contribute to the mechanistic study of circadian clock regulation inherent in polyploidy genome crops, which differ from those of model plants, and thus will be useful for future breeding studies using clock genes.

Coelacanth-specific adaptive genes give insights into primitive evolution for water-to-land transition of tetrapods.

Coelacanth is a group of extant lobe-finned fishes in Sarcopterygii that provides evolutionary information for the missing link between ray-finned fish and tetrapod vertebrates. Its phenotypes, different from actinopterygian fishes, have been considered as primitive terrestrial traits such as cartilages in their fatty fins which are homologous with the humerus and femur. To investigate molecular evolution of coelacanth which led to its divergence into Sarcopterygii, we compared its protein coding sequences with 11 actinopterygian fishes. We identified 47 genes under positive selection specific to coelacanth, when compared to Holostei and Teleostei. Out of these, NCDN and 14 genes were associated with spatial learning and nitrogen metabolism, respectively. In homeobox gene superfamily, we identified coelacanth-specific amino acid substitutions, and also observed that one of replacements in SHOX was shared with extant tetrapods. Such molecular changes may cause primordial morphological change in the common ancestor of sarcopterygians. These results suggest that certain genes such as NCDN, MMS19, TRMT1, ALX1, DLX5 and SHOX might have played a role in the evolutionary transition between aquatic and terrestrial vertebrates.

Pseudo-Reference-Based Assembly of Vertebrate Transcriptomes.

High-throughput RNA sequencing (RNA-seq) provides a comprehensive picture of the transcriptome, including the identity, structure, quantity, and variability of expressed transcripts in cells, through the assembly of sequenced short RNA-seq reads. Although the reference-based approach guarantees the high quality of the resulting transcriptome, this approach is only applicable when the relevant reference genome is present. Here, we developed a pseudo-reference-based assembly (PRA) that reconstructs a transcriptome based on a linear regression function of the optimized mapping parameters and genetic distances of the closest species. Using the linear model, we reconstructed transcriptomes of four different aves, the white leg horn, turkey, duck, and zebra finch, with the Gallus gallus genome as a pseudo-reference, and of three primates, the chimpanzee, gorilla, and macaque, with the human genome as a pseudo-reference. The resulting transcriptomes show that the PRAs outperformed the de novo approach for species with within about 10% mutation rate among orthologous transcriptomes, enough to cover distantly related species as far as chicken and duck. Taken together, we suggest that the PRA method can be used as a tool for reconstructing transcriptome maps of vertebrates whose genomes have not yet been sequenced.