The genome of certain single-celled plankton, known as dinoflagellates, is organized in an incredibly strange and unusual way, according to new research. The findings lay the groundwork for further investigation into these important marine organisms and dramatically expand our picture of what a eukaryotic genome can look like. Researchers from Saudia Arabia’s KAUST (King Abdullah University of Science and Technology), the U.S., and Germany have investigated the genomic organization of the coral-symbiont dinoflagellate Symbiodinium microadriaticum (image). The genome of S. microadriaticum genome had already been sequenced and assembled into segments known as scaffolds but lacked a chromosome-level assembly. The team used a technique known as Hi-C to detect interactions in the dinoflagellate’s chromatin, the combination of DNA and protein that makes up a chromosome. By analyzing these interactions, they could figure out how the scaffolds were connected together into chromosomes, giving them a view into the spatial and structural organization of the genome. A striking finding was that the genes in the genome tended to be organized in alternating unidirectional blocks. “That’s really, really different from what you see in other organisms,” says Octavio Salazar, a PhD student in Manuel Aranda's (PhD) group at KAUST and one of the lead authors of the study. The orientation of genes on a chromosome is usually random. In this case, however, genes were consistently oriented one way and then the other, with the boundaries between blocks showing up clearly in the chromatin interaction data. “Nature can work in a completely different way than we thought,” Salazar said.
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