Adaptive lateral gene transfer in grasses

Descent with modification is the current paradigm for evolution in eukaryotes, but lateral gene transfer (LGT) among members of this domain are increasingly reported. LGT represent a mechanism to bypass many of the limitations of evolution by descent, but little is known about the extent of LGT in eukaryotes, the mechanisms behind this process, and their adaptive significance. To investigate this further we generated a chromosomal level genome assembly for the grass Alloteropsis semialata, a species that has previously been shown to express key C4 photosynthetic genes that were laterally acquired from distantly related grass species. We quantify the extent of grass-to-grass LGT in the A. semialata genome, characterise their genomic context and identify which loci have remained functional. The distribution of each LGT was assessed across the A. semialata phylogeny using resequencing data for multiple populations from Africa, Asia and Australia. We show evidence that the LGTs have been positively selected for, that the simultaneously acquisition of transposable elements may act as a negative balancing cost, and we combine all the information regarding LGT in this species to speculate about possible mechanisms. Overall, our results demonstrate that LGT among eukaryotes can be significant, representing a recurrent source of material for adaptive diversification.