Abstract
BackgroundAmaranth (Amaranthus hypochondriacus) was a food staple among the ancient civilizations of Central and South America that has recently received increased attention due to the high nutritional value of the seeds, with the potential to help alleviate malnutrition and food security concerns, particularly in arid and semiarid regions of the developing world. Here, we present a reference-quality assembly of the amaranth genome which will assist the agronomic development of the species.ResultsUtilizing single-molecule, real-time sequencing (Pacific Biosciences) and chromatin interaction mapping (Hi-C) to close assembly gaps and scaffold contigs, respectively, we improved our previously reported Illumina-based assembly to produce a chromosome-scale assembly with a scaffold N50 of 24.4 Mb. The 16 largest scaffolds contain 98% of the assembly and likely represent the haploid chromosomes (n = 16). To demonstrate the accuracy and utility of this approach, we produced physical and genetic maps and identified candidate genes for the betalain pigmentation pathway. The chromosome-scale assembly facilitated a genome-wide syntenic comparison of amaranth with other Amaranthaceae species, revealing chromosome loss and fusion events in amaranth that explain the reduction from the ancestral haploid chromosome number (n = 18) for a tetraploid member of the Amaranthaceae.ConclusionsThe assembly method reported here minimizes cost by relying primarily on short-read technology and is one of the first reported uses of in vivo Hi-C for assembly of a plant genome. Our analyses implicate chromosome loss and fusion as major evolutionary events in the 2n = 32 amaranths and clearly establish the homoeologous relationship among most of the subgenome chromosomes, which will facilitate future investigations of intragenomic changes that occurred post polyploidization.
Highlights
Amaranth (Amaranthus hypochondriacus) was a food staple among the ancient civilizations of Central and South America that has recently received increased attention due to the high nutritional value of the seeds, with the potential to help alleviate malnutrition and food security concerns, in arid and semiarid regions of the developing world
The chromosome-scale assembly facilitated a genome-wide syntenic comparison of amaranth with other members of the Amaranthaceae, revealing chromosome loss and fusion events in amaranth that explain the reduction from the ancestral haploid chromosome number (n = 18) for a tetraploid member of the Amaranthaceae and providing insights into genome evolution in plants
To improve this short-read assembly (SRA1), we generated 238 million Hi-C-based PE reads and used them to scaffold Short-read assembly 1 (SRA1) with ProximoTM (Phase Genomics), an adapted proximity-guided assembler based on the ligating adjacent chromatin enables scaffolding in situ (LACHESIS) assembler [25]
Summary
Amaranth (Amaranthus hypochondriacus) was a food staple among the ancient civilizations of Central and South America that has recently received increased attention due to the high nutritional value of the seeds, with the potential to help alleviate malnutrition and food security concerns, in arid and semiarid regions of the developing world. Amaranths have a high level of tolerance to abiotic stresses such as salinity, heat, drought, and high UV irradiance [7, 8]. These attributes make amaranth a suitable candidate for further development as a crop species given climate and food security concerns, in developing countries [9]
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