The Amaranth (Amaranthus Hypochondriacus) Genome: Genome, Transcriptome and Physical Map Assembly
Amaranthus hypochondriacus is an emerging pseudo-cereal native to the New World which has garnered increased attention in recent years due to its nutritional quality, in particular its seed protein, and more specifically its high levels of the essential amino acid lysine. It belongs to the Amaranthaceae family, is an ancient paleotetraploid that shows amphidiploid inheritance (2n=32), and has an estimated genome size of 466 Mb. Here we present a high-quality draft genome sequence of the grain amaranth A. hypochondriacus. The genome assembly consisted of 377 Mb in 3,518 scaffolds with an N50 of 371 kb. Repetitive element analysis predicted that 48% of the genome is comprised of repeat sequences, of which Copia-like elements were the most common classified retrotransposon. A transcriptome, consisting of 66,370 contigs, was assembled from eight different tissue and abiotic stress libraries. Annotation of the genome identified 23,059 genes that were supported by our de novo transcriptome assembly, the RefBeet 1.1 gene index and the Uniprot_sprot database. To describe the genetic diversity within the grain amaranths (A. hypochondriacus, A. caudatus, and A. cruentus) and their putative progenitor (A. hybridus) we re-sequenced seven accessions in the genus Amaranthus (four A. hypochondriacus, and one of each A. caudatus, A. cruentus, and A. hybridus), which identified 7,184,636 and 1,760,433 interspecific and intraspecific single nucleotide polymorphisms, respectively. A phylogeny analysis of the re-sequenced accessions substantiated the classification of A. hybridus as the progenitor species of the grain amaranths. Lastly, we generated a physical map for A. hypochondriacus using the BioNano optical mapping platform. The physical map spanned 340 Mb and a hybrid assembly using the BioNano optical genome maps nearly doubled the N50 of the assembly to 697 kb. Moreover, we analyzed synteny between amaranth and Beta vulgaris (sugar beet) and estimated, using Ks analysis, the age of the most recent polyploidization event in amaranth.