DIVERGENT EVOLUTION OF 2 PLASTID GENES, RBCL AND ATPB, IN A NONPHOTOSYNTHETIC PARASITIC PLANT

Plastid DNA (ptDNA) regions for the large subunit of ribulose-1,5-bisp hosphate carboxylase/oxygenase (Rubiso) (rbcL) and the beta-subunit of ATP synthase (atpB) genes of the holoparasite Lathraea clandestina L. were sequenced. These regions were obtained by cloning either a Barn HI endonuclease generated fragment from the Lathraea ptDNA or polymera se chain reaction (PCR) amplified products. The Lathraea ptDNA contain s the entire sequence for the rbcL gene which shares 94.5% homology wi th the Nicotiana tabacum gene, whereas atpB is maintained as a pseudog ene. The intergenic region between divergently transcribed rbcL and at pB genes is shorter (758 bp) in L. clandestina plastid genome in compa rison with N. tabacum (823 bp), however they have a noticeable similar ity, mainly in the rbcL 5'-upstream region. A low level of the rbcL ge ne transcription was detected whereas no atpB transcripts were found i n Lathraea. The plasmid rbcL gene of the hemiparasite Melampyrum prate nse and the autotroph Digitalis purpurea both from the Scrophulariacea e were cloned by PCR amplification and then sequenced. The L. clandest ina rbcL gene is highly homologous to the M. pratense and D. purpurea genes. The data indicate that the evolution of the plastid atpB-rbcL r egion was different in parasites from the Scrophulariaceae and Orobanc haceae families.