Expansion and contraction of the chloroplast inverted repeat in Apiaceae subfamily Apioideae

Chloroplast DNA (cpDNA) restriction site maps for 113 species of Apiaceae ( Umbelliferae) and the allied families Araliaceae and Pittosporaceae were co nstructed for two enzymes and examined for variation in position of J(LB), the junction between the large single copy and inverted repeat regions that is typically contained within the ribosomal protein S10 operon. With the e xception of one large clade in Apiaceae subfamily Apioideae, all species po ssess a J(LB) indistinguishable from that found in the vast majority of ang iosperms. Within this large clade, however, at least one expansion and seve n different contractions of the IR relative to the tobacco J(LB) were detec ted, each ranging in size from similar to1-16 kb. Five of the junction shif ts are parsimony informative and three support major clades delimited in ea rlier phylogenetic studies. In light of cladograms based on previous studie s of restriction site and DNA sequencing data, the IR appears to have expan ded and contracted a minimum of ten times during the evolution of Apioideae , with several presumably identical size variants occurring in parallel. Th e frequency and large size of J(LB) shifts in Apioideae cpDNAs are unpreced ented among angiosperms, indicating that the subfamily represents a model s ystem to study the mechanisms leading to large-scale expansions and contrac tions of the IR.