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Crop Biotech Update

New Assembly for Bread Wheat Genome has 10x Higher Contiguity

August 2, 2017

In a major step towards accuracy and completeness for the wheat genome, a team of scientists from Johns Hopkins present a new assembly that demonstrates the importance of using long, highly-accurate reads for resolving extremely complex, repetitive genomes.

The project aimed to overcome a longstanding challenge for wheat research as common bread wheat has one of the most complex genomes, with 6 copies of each chromosome, enormous numbers of near-identical sequences scattered throughout, and an overall size of more than 15 billion bases. Multiple attempts in the past to assemble the genome have failed.

In 2012, only one-third of the genome was assembled. In 2014, a short-read assembly managed to capture two-thirds of the genome in a highly fragmented assembly, while a subsequent short-read-based effort delivered more sequence but in millions of contigs. According to the authors of the study, this project is the first assembly that contains essentially the entire length of the genome, with more than 15.3 billion bases, and its contiguity is more than ten times better than the partial assemblies published in the past.

The most interesting finding of this study was the delineation of the ancestral plant's contributions to the bread wheat genome (known as the wheat D genome). "By aligning this assembly to the draft genome of Aegilops tauschii, the progenitor of the wheat D genome, we were able to cleanly separate the D genome component from the A and B genomes of hexaploid wheat, which is reported here for the first time," the team explains.

Read more about this research at the PacBio website.