Chromosome-level assemblies of Amaranthus palmeri, Amaranthus retroflexus, and Amaranthus hybridus allow for genomic comparisons and identification of a sex-determining region

Abstract

Amaranthus palmeri (Palmer amaranth), A. retroflexus (redroot pigweed), and A. hybridus (smooth pigweed) are troublesome weeds that are economically damaging to several cropping systems. Collectively referred to as pigweeds, these species are incredibly adaptive and have become successful competitors in diverse agricultural settings. Development of genomic resources for these species promises to facilitate the elucidation of the genetic basis of traits such as biotic and abiotic stress tolerance (e.g., herbicide resistance) and sex determination. Here, we sequenced and assembled chromosome-level genomes of these three pigweed weed species. By combining the haplotype-resolved assembly of A. palmeri with existing restriction site-associated DNA sequencing data, we identified a [~]2.84 Mb region on chromosome 3 of Hap1 that is male-specific and contains 37 genes. Transcriptomic analysis revealed two genes within the male-specific region, RESTORER OF FERTILITY 1 (Rf1) and TLC DOMAIN-CONTAINING PROTEIN (TLC), were upregulated in male individuals across the shoot apical meristem, the floral meristem, and mature flowers, indicating their potential involvement in sex determination in A. palmeri. In addition, we rigorously classified cytochrome P450 genes in all three pigweeds due to their involvement in non-target site herbicide resistance. Finally, we identified contiguous extrachromosomal circular DNA (eccDNA) in A. palmeri, a critical component of glyphosate resistance in this species. The findings of this study advance our understanding of sex determination in A. palmeri and provide genomic resources for elucidating the genetic basis and evolutionary origins of adaptive traits within the genus.