image: Male inflorescence of Balanophora laxiflora. view more
Credit: Image courtesy of Huei-Jiun Su.
Researchers report a nontraditional genetic code in a parasitic land plant. Parasitic plants that do not photosynthesize derive nutrients by forming vascular connections with host plants. Such parasitic plants harbor nonphotosynthetic plastids, which normally perform photosynthesis in land plants and contain their own genomes, but little is known about the plastid genomes of extreme parasitic plants. Jeffrey Palmer, Claude W. dePamphilis, and colleagues sequenced and analyzed the plastid genomes of two species of Balanophora, a fully parasitic mushroom-like plant that produces some of the smallest known flowers. The pair of plastid genomes, around 15.5 kb in size and harboring 19 putatively functional genes, are among the smallest and most compact plastid genomes documented. Both genomes consist largely of adenine (A) and thymine (T) nucleotides, carrying more than 87% A-T content. The authors discovered a novel genetic code in the Balanophora plastids: the triplet codon TAG, which functions as a stop codon during protein synthesis in the canonical code, is reassigned to encode the amino acid tryptophan. Moreover, 14 of the 19 genes in Balanophora plastids are devoted to protein synthesis, despite the loss of all plastid transfer RNA genes for protein synthesis, suggesting that the parasites import the transfer RNAs from the cytosol, with the corresponding genes residing in the Balanophora nucleus or mitochondrion. According to the authors, the findings pave the way for studies of radical genome evolution.
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Article #18-16822: "Novel genetic code and record-setting AT-richness in the highly reduced plastid genome of the holoparasitic plant Balanophora," by Huei-Jiun Su et al.
MEDIA CONTACT: Jeffrey Palmer, Indiana University, Bloomington, IN; e-mail: <jpalmer@indiana.edu>
Journal
Proceedings of the National Academy of Sciences