LOSS OF PHOTOSYNTHETIC AND CHLORORESPIRATORY GENES FROM THE PLASTID GENOME OF A PARASITIC FLOWERING PLANT

PHOTOSYNTHESIS is the hallmark of plant life and is the only plastid metabolic process known to be controlled by plastid genes1,2. The complete loss of photosynthetic ability, however, has occurred on several independent occasions in parasitic flowering plants3,4. Some of these plants are known to lack chlorophyll and certain photosynthetic enzymes4, but it is not known to what extent changes have occurred in the genes encoding the photosynthetic apparatus or whether the plants even maintain a plastid genome. Here we report that the nonphotosynthetic root parasite Epifagus virginiana has a plastid chromosome only 71 kilobases in size, far smaller than any previously characterized land plant plastid genome5. The Epifagus plastid genome has lost most, if not all, of the 30 or more chloroplast genes for photosynthesis and most of a large family of plastid genes, the ndh genes, whose products may be involved in a plastid respiratory chain6-9. The extensive changes in Epifagus plastid gene content must have occurred in a relatively short time (5-50 x 106 yr), because Striga asiatica, a related photosynthetic parasite, has a typical complement of chloroplast genes for photosynthesis and chlororespiration. The plastid genome of Epifagus has retained transcribed ribosomal RNA and ribosomal protein genes, suggesting that it expresses one or more gene products for plastid functions not related to photosynthesis. © 1990 Nature Publishing Group.