Genome assembly of Polygala tenuifolia provides insights into its karyotype evolution and triterpenoid saponin biosynthesis

Polygala tenuifolia is a perennial medicinal plant that has been widely used in traditional Chinese medicine for treating mental diseases.However,the lack of genomic resources limits the insight into its evolutionary and biological characterization.In the present work,we reported the P.tenuifolia genome,the first genome assembly of the Polygalaceae family.We sequenced and assembled this genome by a combination of Illumnina,PacBio HiFi,and Hi-C mapping.The assembly includes 19 pseudochromosomes covering∼92.68%of the assembled genome(∼769.62 Mb).There are 36463 protein-coding genes annotated in this genome.Detailed comparative genome anal-ysis revealed that P.tenuifolia experienced two rounds of whole genome duplication that occurred∼39–44 and∼18–20 million years ago,respectively.Accordingly,we systematically reconstructed ancestral chromosomes of P.tenuifolia and inferred its chromosome evolution trajectories from the common ancestor of core eudicots to the present species.Based on the transcriptomics data,enzyme genes and transcription factors involved in the synthesis of triterpenoid saponin in P.tenuifolia were identified.Further analysis demonstrated that whole-genome duplications and tandem duplications play critical roles in the expansion of P450 and UGT gene families,which contributed to the synthesis of triterpenoid saponins.The genome and transcriptome data will not only provide valuable resources for comparative and functional genomic researches on Polygalaceae,but also shed light on the synthesis of triterpenoid saponin.

Computational Identification of Small Interfering RNA Targets in SARS CoV-2

Dear Editor,At the end of 2019,a new virus,called Severe Acute Respiratory Syndrome Coronavirus 2(SARS-CoV-2)was reported(Benvenuto et al.2020;Zhu et al.2020).The sequences of SARS-CoV-2 reported by different research groups demonstrated that it is a positive strand RNA virus.The sequence of SARS-CoV-2 is approximately 30 kb long,and could encodes spike,envelope,membrane,nucleocapsid proteins,etc.(Phan 2020).These proteins are responsible for replicating the viral genome as well as generating nested transcripts that are used in the synthesis of the viral proteins.