Axillary shoot proliferation and plant regeneration in Euryodendron excelsum H. T. Chang, a critically endangered species endemic to China

Chromosome-level genome assembly and demographic history of Euryodendron excelsum in monotypic genus endemic to China

Euryodendron excelsum is in a monotypic genus Euryodendron, endemic to China. It has intermediate morphisms in the Pentaphylacaceae or Theaceae families, which make it distinct. Due to anthropogenic disturbance, E. excelsum is currently found in very restricted and fragmented areas with extremely small populations. Although much research and effort has been applied towards its conservation, its long-term survival mechanisms and evolutionary history remain elusive, especially from a genomic aspect. Therefore, using a combination of long/short whole genome sequencing, RNA sequencing reads, and Hi-C data, we assembled and annotated a high-quality genome for E. excelsum. The genome assembly of E. excelsum comprised 1,059,895,887 bp with 99.66% anchored into 23 pseudo-chromosomes and a 99.0% BUSCO completeness. Comparative genomic analysis revealed the expansion of terpenoid and flavonoid secondary metabolite genes, and displayed a tandem and/or proximal duplication framework of these genes. E. excelsum also displayed genes associated with growth, development, and defence adaptation from whole genome duplication. Demographic analysis indicated that its fluctuations in population size and its recent population decline were related to cold climate changes. The E. excelsum genome assembly provides a highly valuable resource for evolutionary and ecological research in the future, aiding its conservation, management, and restoration.

Shoot organogenesis and somatic embryogenesis from leaf and petiole explants of endangered Euryodendron excelsum

Euryodendron excelsum H.T. Chang is a rare and endangered woody plant endemic to China. It is very important to conserve and propagate this species from extinction. In this study, leaves and petioles from the axillary shoots in vitro were used as explants to culture on the different plant growth regulator (PGR) woody plant medium (WPM) and establish an efficient shoot proliferation and plant regeneration system. WPM supplemented with 1.0 mg/L 2,4-D induced callus dedifferentiated into buds and somatic embryos on various media,including PGR-free WPM. However, only adventitious shoots formed on WPM with 1.0 mg/L of cytokinins such as 6-benzyladenine (BA), kinetin (KIN) or thidiazuron (TDZ). When another cytokinin, zeatin, was used, somatic embryos were induced directly from From cut surface of these explants. Adventitious roots could be induced from both explants on WPM with 1.0 mg/L α-naphthaleneacetic acid (NAA). Somatic embryos cultured in PGR-free WPM or WPM with 0.2 mg/L NAA developed roots. Plantlets derived from somatic embryos were transferred to a peat: sand (1:1, v/v) substrate, and showed survival rates of 64.3% at 30 days and 54.6% at 90 days. Callus clumps with adventitious shoot buds that were transferred to WPM containing 1.0 mg/L BA and 0.2 mg/L NAA generated a mean 3.3 multiple shoots. Callus-derived shoots regenerated and rooted successfully (100%) on agar-free vermiculite-based WPM with 0.5 μM NAA after 30 d. Plantlets transplanted to peat soil: vermiculite (1:1, v/v) displayed the highest survival (96.7%) after three months.