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This Week in Nature: Sep 8, 2016

In Nature this week, a group of US and Chinese investigators presents a genetic analysis of the improved yields from hybrid rice compared with inbred parent varieties — a phenomenon known as heterosis. They report large-scale genomic mapping for yield-related traits and effects by analyzing over 10,000 rice lines derived from 17 representative hybrid rice crosses, classifying modern hybrid rice varieties into three groups representing different breeding systems. Within each group, the investigators identified a small number of genomic regions from female parents that were associated with heterosis, although these loci varied between the groups. The results of the study inform the genomic architecture of heterosis and may be useful in further rice hybrid breeding.

In Nature Methods, a team of Chinese scientists reports on the use of the genome-editing technology CRISPR/Cas9 to change an oncogenic cellular signal into one that suppresses tumor growth. Working in mice, the researchers modified the piece of RNA that directs CRISPR/Cas9 to its DNA target so that it is turned on by a signal that ordinarily promotes tumor growth and brings a transcriptional activator to two tumor-suppressor genes. In a separate experiment, the group reprogrammed cells so that they induced expression of genes causing cell death when exposed to oncogenic stimulus, which led to smaller tumors in the animals.

And in Nature Genetics, an international research group publishes the genome sequence of Brassica juncea, or mustard greens, shedding new light on the evolution of this agriculturally important plant via polyploidy. B. juncea is an allopolyploid member of the Brassica genus, which consists of three diploid species and two other allopolyploid species. To better understand the plant's origin, the investigators assembled its genome using a combination of shotgun reads, single-molecule long reads, genomic mapping, and genetic mapping. They found that the subgenomes of B. juncea and allopolyploid relative Brassica napus each had independent origins, and that the A subgenomes of B. juncea were of monophyletic origin and evolved into vegetable-use and oil-use subvarieties. They also noted homeolog expression dominance between subgenomes of allopolyploid B. juncea, which facilitated the selection of glucosinolate and lipid metabolism genes in subvarieties used agriculturally.