Phylogeny of tribe Brassiceae (Brassicaceae) based on chloroplast restriction site polymorphisms and nuclear ribosomal internal transcribed spacer and chloroplast trnL intron sequences

Abstract

Using sequence data from the ITS region (internal transcribed spacers ITS-1 and ITS-2 of nuclear DNA and the 5.8 rRNA gene), chloroplast DNA (cpDNA) sequence data from the trnL intron, and cpDNA restriction site polymorphism data, we examined the evolutionary relationships of the tribe Brassiceae (Brassicaceae). A group of approximately 50 genera, it is distinguished by the presence of conduplicate cotyledons and (or) heteroarthrocarpic fruit. cpDNA restriction site data and ITS, trnL, and combined ITS/trnL sequence data were obtained for 22, 104, 94, and 87 taxa in the tribe, respectively. Results from maximum parsimony analyses of the cpDNA and ITS and ITS/trnL sequence data showed a monophyletic origin for the tribe, with the inclusion of controversial members Calepina, Conringia, and Orychophragmus. ITS- and ITS/trnL-based clades corresponded to taxonomic subtribes: Vellinae, Zillinae, and Savignyinae; but as with previous cpDNA studies, there was little support for subtribes Brassicinae, Raphaninae, and Moricandiinae. Although there was no support for the Rapa/Oleracea or Nigra cpDNA lineages, many cpDNA subclades within each of them were evident in the ITS- and ITS/trnL-based phylogeny. The trnL sequence data provided little or no resolution of tribal or subtribal limits. The ITS data indicated polyphyletic origins for Brassica, Diplotaxis, and Erucastrum.Key words: Brassiceae, Calepina, Conringia, Orychophragmus, ITS, trnL, cpDNA restriction site polymorphisms.