The genome sequence of Aloe vera reveals adaptive evolution of drought tolerance mechanisms

Abstract

Aloe vera is a species from Asphodelaceae plant family having unique characteristics such as drought resistance and also possesses numerous medicinal properties. However, the genetic basis of these phenotypes is yet unknown, primarily due to the unavailability of its genome sequence. In this study, we report the first Aloe vera draft genome sequence comprising of 13.83 Gbp and harboring 86,177 coding genes. It is also the first genome from the Asphodelaceae plant family and is the largest angiosperm genome sequenced and assembled till date. Further, we report the first genome-wide phylogeny of monocots with Aloe vera using 1,440 one-to-one orthologs that resolves the genome-wide phylogenetic position of Aloe vera with respect to the other monocots. The comprehensive comparative analysis of Aloe vera genome with the other available high-quality monocot genomes revealed adaptive evolution in several genes of the drought stress response, CAM pathway, and circadian rhythm in Aloe vera. Further, genes involved in DNA damage response, a key pathway in several biotic and abiotic stress response mechanisms, were found to be positively selected. This provides the genetic basis of the evolution of drought stress tolerance capabilities of Aloe vera. This also substantiates the previously suggested notion that the evolution of unique characters in this species is perhaps due to selection and adaptive evolution rather than the phylogenetic divergence or isolation.