Molecular evidence for bicontinental hybridogenous genomic constitution in Lepidium sensu stricto (Brassicaceae) species from Australia and New Zealand

Abstract

Lepidium sensu stricto (s.s.) (Brassicaceae) (ca. 150 species) is distributed worldwide with endemic species on every continent. It is represented in Australia and New Zealand by 19 and seven native species, respectively. In the present study we used a nuclear ribosomal internal transcribed spacer (ITS) phylogeny in comparison with a cpDNA phylogeny to unravel the origin of Australian/New Zealand species. Although phylogenetic relationships within Lepidium s.s. were not fully resolved, the cpDNA data were in agreement with a Californian origin of Lepidium species from Australia/New Zealand. Strongly conflicting signals between the cp- and nuclear DNA phylogenetic analysis clearly indicated hybridogenous genomic constitution of Australian Lepidium s.s. species: All 18 studied Australian/New Zealand Lepidium s.s. species examined shared a Californian cpDNA type. While eleven Australian/New Zealand species appeared to harbor a Californian ITS type, a group of seven species shared a South African ITS type. This pattern is most likely explained by two trans-oceanic dispersals of Lepidium from California and Africa to Australia/New Zealand and subsequent hybridization followed by homogenization of the ribosomal DNA either to the Californian or South African ITS type in the two different lineages. Calibration of our molecular trees indicates a Pliocene/Pleistocene origin of Lepidium in Australia/New Zealand. Low levels of cpDNA and ITS sequence divergence and unresolved topologies within Australian/New Zealand species suggest a rapid and recent radiation of Lepidium after the hybridization event. This coincides with dramatic climatic changes in that geological epoch shaping the composition of the vegetation.

Spatiotemporal Seed Development Analysis Provides Insight into Primary Dormancy Induction and Evolution of theLepidium DELAY OF GERMINATION1Genes

“…Thus, L. oxytrichum was not recognized (and segregated from L. papillosum) until 1915 (Hewson, 1981). In molecular phylogenetic analysis, L. oxytrichum and L. papillosum were recognized as separate species, and they do form a monophyletic lineage (Mummenhoff et al, 2004. Therefore, we verified by trichome morphology and ITS sequence analysis (Supplemental Figs.…”

“…The abundant presence of polyploid Lepidium spp. in Australia implied a reticulate history of the genus on this continent characterized by hybridization/ polyploidization events (Lee et al, 2002;Mummenhoff et al, 2004;Dierschke et al, 2009). Lepidium oxytrichum and L. papillosum differ only in trichome type.…”

“…therein). Intercontinental dispersal of mucilaginous seeds adhering to birds led to a relatively rapid worldwide distribution, forming the basis for adaptations to very different habitats (Mummenhoff et al, 2004;Dierschke et al, 2009). Comparative work with L. sativum and Arabidopsis seeds (Linkies et al, 2009;Graeber et al, 2010Graeber et al, , 2011Voegele et al, 2011) and fruits Mühlhausen et al, 2010) highlights the suitability of the genus Lepidium for cross-species research on diverse developmental aspects.…”

Systematics and phylogeny of the Brassicaceae (Cruciferae): an overview

“…The extensive molecular studies on Lepidium and related genera (Mummenhoff 1995;Bowmann et al 1999;Mummenhoff et al 2001aMummenhoff et al , 2004 were relied on to draw the boundaries of this tribe.…”

Molecular phylogeny and systematics of the tribe Chorisporeae (Brassicaceae)

“…These independent markers are widely applied in phylogenetic studies across the Brassicaceae and have helped in unraveling relationships within and among various taxa and major lineages (e.g., Franzke et al 1998Franzke et al , 2004Al-Shehbaz 2002, 2004;Mummenhoff et al 2004;Lihová et al 2004Lihová et al , 2006aWarwick et al 2004aWarwick et al , b, 2006bWarwick and Sauder 2005;Yue et al 2008;Carlsen et al 2009;Mummenhoff et al 2009;Jordon-Thaden et al 2010). …”