COLINEARITY OF CHLOROPLAST GENOMES IN DIVERGENT ECOTYPES OF THE MARINE DIATOM SKELETONEMA-COSTATUM (BACILLARIOPHYTA)

The chloroplast genomes of three isolates of the marine diatom Skeleto nema costatum (Grev.) Cleve were mapped and found to be 131 +/- 2 kb w ith inverted repeats (IRs) of approximately 20 kb. In contrast to high er plants, the psbA gene mapped to the IR, and rbcS mapped to the same fragment as the rbcL gene in the large single-copy region. The maps o f the three isolates were colinear and revealed as many as 20 site mut ations out of a total of 47 sites. The number of site mutations among isolates was consistent with previous data on their genetic diversity and physiology. Comparisons of gene order among our maps and those of three other diatom species showed that closely related genera retained similar gene orders bur that more distantly related taxa exhibited ex tensive rearrangements. We conclude that simple restriction fragment a nalysis of chloroplast DNA is useful in, comparative studies of diatom populations and species but that other analytical methods are more ap propriate for phylogenetic studies at higher levels.