Sunflowers are a major global crop, producing seeds and oil. In addition, they maintain stable yields under a wide range of environmental conditions, including drought — a useful attribute in a changing climate. On page 148, Badouin et al. report a reference genome for the domesticated sunflower Helianthus annuus L. (H. Badouin et al. Nature 546, 148–152; 2017).
The genome of the sunflower (pictured) has proved difficult to assemble, because it is large (3.6 gigabase long) and highly repetitive. Badouin and colleagues overcame these hurdles using an approach that included single-molecule real-time sequencing of long stretches of DNA, enabling the many similar and related sequences to be pieced together. The authors compared the genome with those of related plants, to trace the sunflower's complex evolutionary history. They identified whole-genome duplication events that had occurred in sunflowers alone or also in several other Asterids — a family of flowering plants that, in addition to sunflowers, includes lettuce, artichoke and coffee.
The researchers then resequenced, at lower coverage, 80 cultivated lines of sunflower, to characterize their genetic diversity and to help identify the genetic basis of agriculturally relevant traits. By carrying out genome-wide association analyses using additional lines, they identified 35 genomic regions associated with flowering time.
Finally, Badouin et al. characterized the gene-expression profiles of sunflower roots, stems, leaves and floral organs, and those of leaves and roots treated with hormones or exposed to stressors such as drought. They then integrated these data into models of the genetic networks that regulate flowering time, seed oil content and quality, which they constructed using information from related plants. The analysis identified both new and previously known candidate genes for each trait, and will be a useful resource for breeding programmes to improve sunflower resilience and oil production.Footnote 1
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Bahcall, O. Sunflowers sequenced. Nature 546, 43 (2017). https://doi.org/10.1038/546043a