The chloroplast rpl2 intron and ORF184 as phylogenetic markers in the legume tribe Desmodieae

A previous extensive survey showed that most but not all members of the papilionoid tribe Desmodieae lack the intron for the chloroplast gene rpl2 and partially or completely lack the open reading frame ORF184. We extended the survey of Desmodieae to include all 26 genera recognized in the most recent comprehensive taxonomic treatment of the tribe, and use slot blot hybridization with gene-or intron-specific probes for all taxa, polymerase chain reaction amplification across the rpl2 intron region for a subset of taxa, and DNA sequencing across the rpl2 intron/exon boundary in representatives of selected genera (Desmodium, Lepesdeza, and Phylacium). Our results indicate that rpl2 intron is absent from both genera of the largest subtribe, Desmodiinae, and from core Lespedezinae (Campylotropis, Kummerowia, and Lespedeza). It is indicated as present in both genera of Bryinae and in two Lespedezinae genera (Neocollettia and Phylacium). In contrast to the rpl2 intron, the pattern of ORF184 loss in Desmodiinae and Lespedezinae was extremely complex and difficult to interpret from slot blots, but consistent either with partial deletion or extensive sequence divergence. Bryinae showed no such evidence of loss or partial deletion. In agreement with the distribution of the rpl2 intron, Bryinae have been considered to have affinities outside Desmodieae, while both Phylacium and Neocollettia are anomalous within Lespedezinae. Thus the rpl2 intron loss may represent a synapomorphy for a ''core'' Desmodieae (Desmodiinae and Lespedezinae).