MULTIPLE INDEPENDENT LOSSES OF 2 GENES AND ONE INTRON FROM LEGUME CHLOROPLAST GENOMES

The losses of genes or introns from the chloroplast genome are of pote ntial utility as phylogenetic characters. Previous broad surveys of an giosperms, along with sequencing studies in Pisum sativum, uncovered s everal instances of variation for such characters within the Leguminos ae. Using a slot blot hybridization method that did not require high m olecular weight DNA, probes for sir genes and three introns typically found in angiosperm chloroplast genomes were used to screen 392 legume genera, representing all three subfamilies and 50 out of 51 tribes, a nd 48 genera from 26 other families of dicots. Few cases of chloroplas t gene or intron loss from chloroplast genomes were observed among non legumes or within the legume subfamilies Mimosoideae and Caesalpinioid eae, but numerous apparent losses were observed in the large subfamily Papilionoideae. Certain cases of suspected losses were tested by poly merase chain reaction. The genes rp12 and rbcL appear to be present in all taxa surveyed, and virtually all possess accD. In contrast, ORF18 4 and rps16 each appear to have been lost multiple, independent times within Leguminosae, while all members of the family appear to lack rp1 22. The intron of rp12 has likely been lost at least four times within the family, and its absence is a synapomorphy for a core group of the papilionoid tribe Desmodieae. No convincing evidence of loss was obse rved among legumes for the introns of trnI and rpl16. These results in dicate that gene or intron loss characters may often be homoplastic. I ntron losses are a more reliable and valuable class of phylogenetic ch aracters than are gene losses.