Physical map and gene localization on sunflower (Helianthus annuus) chloroplast DNA: evidence for an inversion of a 23.5-kbp segment in the large single copy region

As a first step in the study of chloroplast genome variability in the genus Helianthus, a physical restriction map of sunflower (Helianthus annuus) chloroplast DNA (cpDNA) has been constructed using restriction endonucleases BamH I, Hind III, Pst I, Pvu II and Sac. I. Sunflower circular DNA contains an inverted repeat structure with the two copies (23 kbp each) separated by a large (86 kbp) and a small (20 kbp) single copy region. Its total length is therefore about 152 kbp. Sunflower cpDNA is essentially colinear with that of tobacco with the exception of an inversion of a 23.5-kbp segment in the large single copy region. Gene localization on the sunflower cpDNA and comparison of the gene map with that from tobacco chloroplasts have revealed that the endpoints of the inversion are located between the trnT and trnE genes on the one hand, and between the trnG and trnS genes on the other hand.Analysis of BamH I restriction fragment patterns of H. annuus, H. occidentalis ssp. plantagineus, H. grossesseratus, H. decapetalus, H. giganteus, H. maximiliani and H. tuberosus cpDNAs suggests that structural variations are present in the genus Helianthus.