The genus Chenopodium L. is characterized by its wide geographic distribution and ecological adaptability. Species such as quinoa (Chenopodium quinoa Willd.) have served as domesticated staple crops for centuries. Wild Chenopodium species exhibit diverse niche adaptations and are important genetic reservoirs for beneficial agronomic traits, including disease resistance and climate hardiness. To harness the potential of the wild taxa for crop improvement, we developed a Chenopodium pangenome through the assembly and comparative analyses of 12 Chenopodium species that encompass the eight known genome types (A-H). Six of the species are new chromosome-scale assemblies, and many are polyploids; thus, a total of 20 genomes were included in the pangenome analyses. We show that the genomes vary dramatically in size with the D genome being the smallest (∼370 Mb) and the B genome being the largest (∼700 Mb) and that genome size was correlated with independent expansions of the Copia and Gypsy LTR retrotransposon families, suggesting that transposable elements have played a critical role in the evolution of the Chenopodium genomes. We annotated a total of 33,457 pan-Chenopodium gene families, of which ∼65% were classified as shell (2% private). Phylogenetic analysis clarified the evolutionary relationships among the genome lineages, notably resolving the taxonomic placement of the F genome while highlighting the uniqueness of the A genome in the Western Hemisphere. These genomic resources are particularly important for understanding the secondary and tertiary gene pools available for the improvement of the domesticated chenopods while furthering our understanding of the evolution and complexity within the genus.

• MeSH
• Chenopodium * genetics   MeSH
• Genome Size MeSH
• Phylogeny MeSH
• Genome, Plant * MeSH
• Terminal Repeat Sequences * genetics   MeSH
• Evolution, Molecular * MeSH
• Retroelements MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Retroelements MeSH

Dormancy and heteromorphism are innate seed properties that control germination timing through adaptation to the prevailing environment. The degree of variation in dormancy depth within a seed population differs considerably depending on the genotype and maternal environment. Dormancy is therefore a key trait of annual weeds to time seedling emergence across seasons. Seed heteromorphism, the production of distinct seed morphs (in color, mass or other morphological characteristics) on the same individual plant, is considered to be a bet-hedging strategy in unpredictable environments. Heteromorphic species evolved independently in several plant families and the distinct seed morphs provide an additional degree of variation. Here we conducted a comparative morphological and molecular analysis of the dimorphic seeds (black and brown) of the Amaranthaceae weed Chenopodium album. Freshly harvested black and brown seeds differed in their dormancy and germination responses to ambient temperature. The black seed morph of seedlot #1 was dormant and 2/3rd of the seed population had non-deep physiological dormancy which was released by after-ripening (AR) or gibberellin (GA) treatment. The deeper dormancy of the remaining 1/3rd non-germinating seeds required in addition ethylene and nitrate for its release. The black seeds of seedlot #2 and the brown seed morphs of both seedlots were non-dormant with 2/3rd of the seeds germinating in the fresh mature state. The dimorphic seeds and seedlots differed in testa (outer seed coat) thickness in that thick testas of black seeds of seedlot #1 conferred coat-imposed dormancy. The dimorphic seeds and seedlots differed in their abscisic acid (ABA) and GA contents in the dry state and during imbibition in that GA biosynthesis was highest in brown seeds and ABA degradation was faster in seedlot #2. Chenopodium genes for GA and ABA metabolism were identified and their distinct transcript expression patterns were quantified in dry and imbibed C. album seeds. Phylogenetic analyses of the Amaranthaceae sequences revealed a high proportion of expanded gene families within the Chenopodium genus. The identified hormonal, molecular and morphological mechanisms and dormancy variation of the dimorphic seeds of C. album and other Amaranthaceae are compared and discussed as adaptations to variable and stressful environments.

• Keywords
• abscisic acid, coat-imposed dormancy, gibberellins, hormone metabolism, seed coat properties, seed heteromorphism, thermal time modelling, weed seed bank,
• Publication type
• Journal Article MeSH

Djulis (Chenopodium formosanum Koidz.) is a crop grown since antiquity in Taiwan. It is a BCD-genome hexaploid (2n = 6x = 54) domesticated form of lambsquarters (C. album L.) and a relative of the allotetraploid (AABB) C. quinoa. As with quinoa, djulis seed contains a complete protein profile and many nutritionally important vitamins and minerals. While still sold locally in Taiwanese markets, its traditional culinary uses are being lost as diets of younger generations change. Moreover, indigenous Taiwanese peoples who have long safeguarded djulis are losing their traditional farmlands. We used PacBio sequencing and Hi-C-based scaffolding to produce a chromosome-scale, reference-quality assembly of djulis. The final genome assembly spans 1.63 Gb in 798 scaffolds, with 97.8% of the sequence contained in 27 scaffolds representing the nine haploid chromosomes of each sub-genome of the species. Benchmarking of universal, single-copy orthologs indicated that 98.5% of the conserved orthologous genes for Viridiplantae are complete within the assembled genome, with 92.9% duplicated, as expected for a polyploid. A total of 67.8% of the assembly is repetitive, with the most common repeat being Gypsy long terminal repeat retrotransposons, which had significantly expanded in the B sub-genome. Gene annotation using Iso-Seq data from multiple tissues identified 75,056 putative gene models. Comparisons to quinoa showed strong patterns of synteny which allowed for the identification of homoeologous chromosomes, and sub-genome-specific sequences were used to assign homoeologs to each sub-genome. These results represent the first hexaploid genome assembly and the first assemblies of the C and D genomes of the Chenopodioideae subfamily.

• Keywords
• Gypsy, LTR, chromosome-scale, long-read sequencing, polyploid evolution, retrotransposon,
• MeSH
• Chenopodium * genetics   MeSH
• Chromosomes, Plant genetics   MeSH
• Genome, Plant MeSH
• Polyploidy MeSH
• Synteny MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH