A chromosome-scale genome assembly of Artemisia argyi reveals unbiased subgenome evolution and key contributions of gene duplication to volatile terpenoid diversity.

Artemisia argyi Lévl. et Vant., a perennial Artemisia herb with an intense fragrance, is widely used in traditional medicine in China and many other Asian countries. Here, we present a chromosome-scale genome assembly of A. argyi comprising 3.89 Gb assembled into 17 pseudochromosomes. Phylogenetic and comparative genomic analyses revealed that A. argyi underwent a recent lineage-specific whole-genome duplication (WGD) event after divergence from Artemisia annua, resulting in two subgenomes. We deciphered the diploid ancestral genome of A. argyi, and unbiased subgenome evolution was observed. The recent WGD led to a large number of duplicated genes in the A. argyi genome. Expansion of the terpene synthase (TPS) gene family through various types of gene duplication may have greatly contributed to the diversity of volatile terpenoids in A. argyi. In particular, we identified a typical germacrene D synthase gene cluster within the expanded TPS gene family. The entire biosynthetic pathways of germacrenes, (+)-borneol, and (+)-camphor were elucidated in A. argyi. In addition, partial deletion of the amorpha-4,11-diene synthase (ADS) gene and loss of function of ADS homologs may have resulted in the lack of artemisinin production in A. argyi. Our study provides new insights into the genome evolution of Artemisia and lays a foundation for further improvement of the quality of this important medicinal plant.

Insights into angiosperm evolution, floral development and chemical biosynthesis from the Aristolochia fimbriata genome.

Aristolochia, a genus in the magnoliid order Piperales, has been famous for centuries for its highly specialized flowers and wide medicinal applications. Here, we present a new, high-quality genome sequence of Aristolochia fimbriata, a species that, similar to Amborella trichopoda, lacks further whole-genome duplications since the origin of extant angiosperms. As such, the A. fimbriata genome is an excellent reference for inferences of angiosperm genome evolution, enabling detection of two novel whole-genome duplications in Piperales and dating of previously reported whole-genome duplications in other magnoliids. Genomic comparisons between A. fimbriata and other angiosperms facilitated the identification of ancient genomic rearrangements suggesting the placement of magnoliids as sister to monocots, whereas phylogenetic inferences based on sequence data we compiled yielded ambiguous relationships. By identifying associated homologues and investigating their evolutionary histories and expression patterns, we revealed highly conserved floral developmental genes and their distinct downstream regulatory network that may contribute to the complex flower morphology in A. fimbriata. Finally, we elucidated the genetic basis underlying the biosynthesis of terpenoids and aristolochic acids in A. fimbriata.

A chromosome-scale reference genome of Aquilegia oxysepala var. kansuensis.

The genus Aquilegia (Ranunculaceae) has been cultivated as ornamental and medicinal plants for centuries. With petal spurs of strikingly diverse size and shape, Aquilegia has also been recognized as an excellent system for evolutionary studies. Pollinator-mediated selection for longer spurs is believed to have shaped the evolution of this genus, especially the North American taxa. Recently, however, an opposite evolutionary trend was reported in an Asian lineage, where multiple origins of mini- or even nonspurred morphs have occurred. Interesting as it is, the lack of genomic resources has limited our ability to decipher the molecular and evolutionary mechanisms underlying spur reduction in this special lineage. Using long-read sequencing (PacBio Sequel), in combination with optical maps (BioNano DLS) and Hi-C, we assembled a high-quality reference genome of A. oxysepala var. kansuensis, a sister species to the nonspurred taxon. The final assembly is approximately 293.2 Mb, 94.6% (277.4 Mb) of which has been anchored to 7 pseudochromosomes. A total of 25,571 protein-coding genes were predicted, with 97.2% being functionally annotated. When comparing this genome with that of A. coerulea, we detected a large rearrangement between Chr1 and Chr4, which might have caused the Chr4 of A. oxysepala var. kansuensis to partly deviate from the "decaying" path that was taken before the split of Aquilegia and Semiaquilegia. This high-quality reference genome is fundamental to further investigations on the development and evolution of petal spurs and provides a strong foundation for the breeding of new horticultural Aquilegia cultivars.

In silico identification and structure function analysis of a putative coclaurine N-methyltransferase from Aristolochia fimbriata.

In this study we isolated and performed in silico analysis of a putative coclaurine N-methyltransferase (CNMT) from the basal angiosperm Aristolochia fimbriata. The Aristolochiaceae plant family produces alkaloids similar to the Papavaraceae family, and CNMTs are central enzymes in biosynthesis pathways producing compounds of ethnopharmacological interest. We used bioinformatics and computational tools to predict a three-dimensional homology model and to investigate the putative function of the protein and its mechanism for methylation. The putative CNMT is a unique (S)-adenosyl-L-methionine (SAM)-dependent N-methyltransferase, catalyzing transfer of a methyl group from SAM to the amino group of coclaurine. The model revealed a mixed α/ß structure comprising seven twisted ß-strands surrounded by twelve α-helices. Sequence comparisons and the model indicate an N-terminal catalytic Core domain and a C-terminal domain, of which the latter forms a pocket for coclaurine. An additional binding pocket for SAM is connected to the coclaurine binding pocket by a small opening. CNMT activity is proposed to follow an SN2-type mechanism as observed for a similarly conformed enzyme. Residues predicted for the methyl transfer reaction are Tyr79 and Glu96, which are conserved in the sequence from A. fimbriata and in homologous N-methyltransferases. The isolated CNMT is the first to be investigated from any basal angiosperm.