Zhejiang University: Genome-wide introgression between two sympatric Asian oak species

The genus Quercus, commonly known as oaks, is one of the most evolutionary successful genera in the Northern Hemisphere in terms of species diversity, biomass and distribution range. Oaks can usually live up to a few hundred years and during the long lifespan they exhibit high tolerance to various abiotic and biotic threats. Meanwhile, oaks are also well known for their extensive interspecific gene flow, which is believed well helpful for their wide dispersal. These traits make Quercus an ideal genus for studying adaptive introgression.

Recently, the research team led by Prof. CHEN Jun at the Zhejiang University College of Life Sciences published an article entitled “Genome-wide analyses of introgression between two sympatric Asian oak species” in Nature Ecology & Evolution. Their research focused on two sympatric Asian oak species of wide distribution ranges — Quercus acutissima and Q. variabili — to explore how introgression can assist each other to rapidly adapt to various environmental conditions.

In this study, Ph.D. students collected samples in 15 provinces of China and generated a chromosomal-level genome assembly of high-quality, population genomic re-sequences and transcriptome data to investigate the correlation between introgression patterns, the recombination rate, genetic variations of local adaptation, and gene expression regulation. Introgressed regions across the genome were found mainly determined by the genetic divergence and environmental condition. The more similar environment they live in, the more likely the two oak species are to exchange in same genomic regions. Adaptive introgressed mutations were maintained by natural selection in four long chromosomal stretches due to suppressed recombination rate, which may be caused by chromosome inversions induced by the insert of transposable elements. Most adaptive introgressed mutations are located in cis-regulatory elements formed by TE insertions and change gene expression level responding to environmental stimulus. On summary, similar environmental condition would lead to similar genetic exchange and finally to similar expression profiles between oaks.

This study provides a new insight into the genetic mechanisms of introgression and environmental adaptation in sympatric species.