Cytokinin signaling promotes root secondary growth and bud formation in Panax ginseng.

Background: Panax ginseng, one of the valuable perennial medicinal plants, stores numerous pharmacological substrates in its storage roots. Given its perennial growth habit, organ regeneration occurs each year, and cambium stem cell activity is necessary for secondary growth and storage root formation. Cytokinin (CK) is a phytohormone involved in the maintenance of meristematic cells for the development of storage organs; however, its physiological role in storage-root secondary growth remains unknown. Methods: Exogenous CK was repeatedly applied to P. ginseng, and morphological and histological changes were observed. RNA-seq analysis was used to elucidate the transcriptional network of CK that regulates P. ginseng growth and development. The HISTIDINE KINASE 3 (PgHK3) and RESPONSE REGULATOR 2 (PgRR2) genes were cloned in P. ginseng and functionally analyzed in Arabidopsis as a two-component system involved in CK signaling. Results: Phenotypic and histological analyses showed that CK increased cambium activity and dormant axillary bud formation in P. ginseng, thus promoting storage-root secondary growth and bud formation. The evolutionarily conserved two-component signaling pathways in P. ginseng were sufficient to restore CK signaling in the Arabidopsis ahk2/3 double mutant and rescue its growth defects. Finally, RNA-seq analysis of CK-treated P. ginseng roots revealed that plant-type cell wall biogenesis-related genes are tightly connected with mitotic cell division, cytokinesis, and auxin signaling to regulate CK-mediated P. ginseng development. Conclusion: Overall, we identified the CK signaling-related two-component systems and their physiological role in P. ginseng. This scientific information has the potential to significantly improve the field-cultivation and biotechnology-based breeding of ginseng.

A chromosome-level genome assembly of Korean mint (Agastache rugosa).

Agastache rugosa, also known as Korean mint, is a perennial plant from the Lamiaceae family that is traditionally used for various ailments and contains antioxidant and antibacterial phenolic compounds. Molecular breeding of A. rugosa can enhance secondary metabolite production and improve agricultural traits, but progress in this field has been delayed due to the lack of chromosome-scale genome information. Herein, we constructed a chromosome-level reference genome using Nanopore sequencing and Hi-C technology, resulting in a final genome assembly with a scaffold N50 of 52.15 Mbp and a total size of 410.67 Mbp. Nine pseudochromosomes accounted for 89.1% of the predicted genome. The BUSCO analysis indicated a high level of completeness in the assembly. Repeat annotation revealed 561,061 repeat elements, accounting for 61.65% of the genome, with Copia and Gypsy long terminal repeats being the most abundant. A total of 26,430 protein-coding genes were predicted, with an average length of 1,184 bp. The availability of this chromosome-scale genome will advance our understanding of A. rugosa's genetic makeup and its potential applications in various industries.

The complete chloroplast genome of Ziziphus jujuba cv. Bokjo (Rhamnaceae).

We have sequenced the Ziziphus jujuba cv. Bokjo chloroplast genome by de novo assembly using next-generation sequencing. The complete circular chloroplast genome consisted of 161,714 bp and contained four parts: a large single-copy (LSC) region of 89,323 bp, a small single-copy (SSC) region of 19,361 bp, and two inverted repeat regions (IRa and IRb) of 26,515 bp each. The genome annotation predicted a total of 110 genes, including 76 protein-coding genes, 30 tRNA genes, and four rRNA genes. Phylogenetic analysis demonstrated the close taxonomic relationship between Z. jujuba cv. Bokjo and two other members of the Ziziphus genus, Z. spina-christi and Z. mauritiana. We found 135 polymorphic loci, 63 single nucleotide polymorphism (SNP) and 72 insertion-deletion (InDel), from the comparison of Z. jujuba cultivar Bokjo and Z. jujuba reference (NC_030299). The polymorphic loci could be used for the differentiation of Z. jujuba genetic resources and for breeding in the future.

The complete chloroplast genome of Paeonia cv. Hwang-Moran (Paeoniaceae).

The complete chloroplast genome of Paeonia cv. Hwang-Moran (PHM), a yellow flowering tree peony, was de novo assembled and characterized from high-throughput next-generation sequencing data. The total length of the circular PHM chloroplast genome was 152,519 bp, including a large single-copy (LSC) region of 84,214 bp, a small single-copy (SSC) region of 17,026 bp, and a pair of inverted repeat regions (IRs) of 25,640 bp. The entire chloroplast genome contained 111 genes, including 77 protein-coding genes, 30 tRNAs, and four rRNAs. A phylogenetic tree constructed using the PHM and related chloroplast genome sequences revealed its close taxonomic relationship with P. ludlowii within the genus Paeonia.

Development of 18 microsatellite markers for Atractylodes japonica.

PREMISE: Atractylodes japonica (Asteraceae) is endemic to East Asia, where its rhizomes are used in traditional medicine. To investigate the genetic diversity of this species, we developed polymorphic microsatellite markers. METHODS AND RESULTS: We obtained a total of 175,825 simple sequence repeat (SSR) loci using the Illumina HiSeq 2500 system. Eighteen polymorphic SSR primer pairs were selected to determine heterozygosity levels and allele numbers in 80 individuals from four A. japonica populations. The levels of observed and expected heterozygosity ranged from 0.000 to 1.000 and from 0.133 to 0.892, respectively. Cross-amplification in the related species A. macrocephala and A. lancea was successful in 15 and 14 of the 18 markers, respectively. CONCLUSIONS: These microsatellite markers will be useful for future studies involving A. japonica population genetics and breeding.

The complete chloroplast genome of Paeonia lactiflora Pall. (Paeoniaceae).

The complete chloroplast genome sequence of Paeonia lactiflora was obtained by de novo assembly using next-generation sequencing. The circular molecule of the genome constituted of four parts, with 152,731 bp in the complete chloroplast genome, including a large single-copy (LSC) region of 84,402 bp, a small single-copy (SSC) region of 16,969 bp, and two inverted repeat (IRa and IRb) regions of 25,680 bp each. The genome annotation predicted a total of 111 genes, including 77 protein-coding genes, 30 tRNA genes, and 4 rRNA genes. Phylogenetic analysis showed the close taxonomical relationship to P. veitchii.

Development of Genome-Wide SSR Markers from Angelica gigas Nakai Using Next Generation Sequencing.

Angelica gigas Nakai is an important medicinal herb, widely utilized in Asian countries especially in Korea, Japan, and China. Although it is a vital medicinal herb, the lack of sequencing data and efficient molecular markers has limited the application of a genetic approach for horticultural improvements. Simple sequence repeats (SSRs) are universally accepted molecular markers for population structure study. In this study, we found over 130,000 SSRs, ranging from di- to deca-nucleotide motifs, using the genome sequence of Manchu variety (MV) of A. gigas, derived from next generation sequencing (NGS). From the putative SSR regions identified, a total of 16,496 primer sets were successfully designed. Among them, we selected 848 SSR markers that showed polymorphism from in silico analysis and contained tri- to hexa-nucleotide motifs. We tested 36 SSR primer sets for polymorphism in 16 A. gigas accessions. The average polymorphism information content (PIC) was 0.69; the average observed heterozygosity (HO) values, and the expected heterozygosity (HE) values were 0.53 and 0.73, respectively. These newly developed SSR markers would be useful tools for molecular genetics, genotype identification, genetic mapping, molecular breeding, and studying species relationships of the Angelica genus.