The chloroplast genome arrangement of Lobelia thuliniana (Lobeliaceae):: expansion of the inverted repeat in an ancestor of the Campanulales

A clone-bank of Sac I restriction fragments was constructed from the chloroplast DNA (cpDNA) of Lobelia thuliniana E. B. KNOX (Lobeliaceae). These cloned fragments and a set of 106 clones spanning the tobacco chloroplast genome were used as probes to determine the cpDNA restriction fragment arrangement for Sac I and six other restriction enzymes (BamH I, EcoR V, Hind III, Nci I, Pst I, and Xho I) and the chloroplast genome arrangement of L. thuliniana relative to tobacco, which has been fully sequenced and is collinear with the hypothesized ancestral genome arrangement of angiosperms. The results confirm and refine our previous understanding of the chloroplast genome arrangement in the large single-copy region (LSC) and reveal (1) a roughly 11 kilobase (kb) expansion of the inverted repeat (IR) into the small single-copy region (SSC) and (2) apparent sequence divergence of the DNA segment in L. thuliniana that corresponds to ORF1901 in tobacco. The expansion of the IR into the SSC is present in all other examined members of Lobeliaceae, Cyphiaceae, and Campanulaceae, which indicates that the IR expansion was an early event in the cpDNA evolution of the Campanulales. The IR expansion into the SSC was not present in Sphenoclea, which additionally supports exclusion of this genus from the Campanulacene.