Variation of the Rdr1 gene insertion in wild populations of Nicotiana benthamiana (Solanaceae) and insights into recent species divergence

Abstract

SummaryOne of the most commonly encountered and frequently cited laboratory organisms worldwide is classified taxonomically as Nicotiana benthamiana (Solanaceae), an accession of which, typically referred to as LAB, is renowned for its unique susceptibility to a wide range of plant viruses and hence capacity to be transformed using a variety of methods. However, the origin and age of LAB and the evolution of N. benthamiana across its wide distribution in Australia remains relatively underexplored.Here, we have used multispecies coalescent methods on genome-wide single nuclear polymorphisms (SNPs) to assess species limits, phylogenetic relationships and divergence times within N. benthamiana.Our results show that the previous taxonomic concept of this species in fact comprises five geographically, morphologically and genetically distinct species, one of which includes LAB.Remarkably, we provide clear evidence that LAB is closely related to accessions collected further north in the Northern Territory; this species split much earlier from their common ancestor than the other four in this clade and is morphologically the most distinctive. Furthermore, this long-isolated species typically grows in sheltered sites in subtropical/tropical monsoon areas of northern Australia, contradicting the previously advanced hypothesis that this species is an extremophile that has traded viral resistance for precocious development.