Plant Genetics: Plastid Genomes — Lost in Translation?

RESEARCH HIGHLIGHTS

Nature Reviews Genetics | AOP, published online 25 March 2014; doi:10.1038/nrg3717

carried out transcriptome sequencing PLANT GENETICS of Polytomella parva to see whether they could identify any transcripts of Plastid genomes — nuclear-encoded, plastid-targeted proteins. “Importantly, we were lost in translation? unable to identify any nuclear genes associated with the expression, Macmillan New Zealand Many eukaryotic lineages have were only replication or repair of plastid DNA,” lost the ability to photosynthesize able to identify explains Smith. but have retained plastids — non-functional fragments of The plastid genomes of membrane-bound organelles that plastid genes, and phylogenetic non-photosynthetic plants are usually typically contain a small DNA analyses led the authors to suggest smaller than those of photosynthetic genome — that continue to carry out that these fragments might have plants; although many genes are often metabolic functions. Researchers integrated into the nuclear DNA lost, most plastids contain several have previously suggested that the through horizontal gene transfer genes that are considered essential. plastid genome is essential because it from the host plant Tetrastigma. “It’s “These results are surprising because has been widely preserved. However, always a problem trying to prove a even among plants that don’t do two separate studies now provide negative,” says Michael Purugganan, photosynthesis, a plastid genome had evidence for plastid genome loss a senior author of the Molina study, always been seen,” says Purugganan. in distinct non-photosynthetic “but we made sure we used multiple Both teams plan on confirming and green plants. Jeanmaire Molina and computational techniques to try to expanding this work in the future. colleagues focused on the parasitic find a plastid genome, and we also evidence Bryony Jones flowering plant genus Rafflesia, performed several experimental for plastid and the other study by David Roy controls.” ORIGINAL RESEARCH PAPERS Smith, D. R. & genome loss Smith and Robert Lee focused on the Similarly, despite being able to Lee, R. W. A plastid without a genome: evidence in distinct non- free-living non-photosynthetic green identify sequencing reads from the from the nonphotosynthetic green alga algae Polytomella. Polytomella nuclear and mitochondrial Polytomella. Plant Physiol. http://dx.doi. photosynthetic org/10.1104/pp.113.233718 (2014) | Molina, J. Both teams used next-generation genomes, Smith and Lee were unable et al. Possible loss of the chloroplast genome in green plants sequencing of the entire DNA to identify any Polytomella sequencing the parasitic flowering plant Rafflesia lagascae content of the plants to look for reads of an obvious plastid genome (Rafflesiaceae). Mol. Biol. Evol. http://dx.doi. org/10.1093/molbev/msu051 (2014) plastid DNA. Molina and colleagues origin. In addition, Smith and Lee

NATURE REVIEWS | GENETICS VOLUME 15 | MAY 2014