The complete chloroplast genome of Rhododendron huadingense (Ericaceae).

Rhododendron huadingense is an important horticultural plant that belongs to the Ericaceae family. In this study, the chloroplast genome sequence of R. huadingense is reported. The chloroplast genome of R. huadingense was 198,952 bp in length and had an angiosperm-typical quadripartite structure with a large single-copy (LSC) region of 108,557 bp, a small single-copy (SSC) region of 53 bp, and two inverted repeat regions (IRs) of 45,171 bp. One hundred and thirteen unique genes including 79 protein-coding genes, 30 transfer RNA (tRNA) genes, and four ribosomal RNA (rRNA) genes were identified in the chloroplast genome. Further phylogenetic analysis revealed a close relationship between R. huadingense and R. molle. The complete chloroplast genome of R. huadingense provides valuable genetic information for the phylogeny, varieties breeding and sustainable utilization of this species.

The chromosome-scale genome of Phoebe bournei reveals contrasting fates of terpene synthase (TPS)-a and TPS-b subfamilies.

Terpenoids, including aromatic volatile monoterpenoids and sesquiterpenoids, function in defense against pathogens and herbivores. Phoebe trees are remarkable for their scented wood and decay resistance. Unlike other Lauraceae species investigated to date, Phoebe species predominantly accumulate sesquiterpenoids instead of monoterpenoids. Limited genomic data restrict the elucidation of terpenoid variation and functions. Here, we present a chromosome-scale genome assembly of a Lauraceae tree, Phoebe bournei, and identify 72 full-length terpene synthase (TPS) genes. Genome-level comparison shows pervasive lineage-specific duplication and contraction of TPS subfamilies, which have contributed to the extreme terpenoid variation within Lauraceae species. Although the TPS-a and TPS-b subfamilies were both expanded via tandem duplication in P. bournei, more TPS-a copies were retained and constitutively expressed, whereas more TPS-b copies were lost. The TPS-a genes on chromosome 8 functionally diverged to synthesize eight highly accumulated sesquiterpenes in P. bournei. The essential oil of P. bournei and its main component, ß-caryophyllene, exhibited antifungal activities against the three most widespread canker pathogens of trees. The TPS-a and TPS-b subfamilies have experienced contrasting fates over the evolution of P. bournei. The abundant sesquiterpenoids produced by TPS-a proteins contribute to the excellent pathogen resistance of P. bournei trees. Overall, this study sheds light on the evolution and adaptation of terpenoids in Lauraceae and provides valuable resources for boosting plant immunity against pathogens in various trees and crops.

Colchicine-Induced Polyploidy in Rhododendron fortunei Lindl.

Polyploidy in Rhododendron fortunei has great potential to improve its horticultural and commercial value, and to also meet market demands. In this study, a feasible method for polyploid induction in R. fortunei via colchicine treatment was established, and the obtained polyploid plants were identified and characterized. As a result, the stem bases of tissue-cultured plantlets treated with 0.1% colchicine for 24 h showed the highest polyploid induction with a rate of 36.67%. By flow cytometric analysis, 69 tetraploids and 29 octoploids were identified in the regenerated plants that were examined. Phenotypic analysis indicated that the leaves of tetraploid and octoploid plants were smaller, rounder and thicker with more abundant and longer epidermal hairs than those of diploids. Furthermore, the stomata of polyploids were larger and sparser than those of diploids. An increase in chlorophyll content was also detected in polyploids, which resulted in darker green leaves. In conclusion, our study established an effective method to induce polyploidy in R. fortunei, which could be used to develop new genetic resources for breeding R. fortunei and other Rhododendron species in the future.