Sweet osmanthus (Osmanthus fragrans) is famous in China for its flowers and contains four groups: Albus, Luteus, Aurantiacus, and Asiaticus. Understanding the relationships among these groups and the genetic mechanisms of flower color and aroma biosynthesis are of tremendous interest. In this study, we sequenced representative varieties from two of the four sweet osmanthus groups. Multi-omic and phylogenetic analyses of varieties from each of the four groups showed that Asiaticus split first within the species, followed by Aurantiacus and the sister groups Albus and Luteus. We show that the difference in flower color between Aurantiacus and the other three groups was caused by a 4-bp deletion in the promoter region of carotenoid cleavage dioxygenase 4 (OfCCD4) that leads to expression decrease. In addition, we identified 44 gene pairs exhibiting significant structural differences between the multi-seasonal flowering variety ‘Rixianggui’ in the Asiaticus group and other autumn flowering varieties. Through correlation analysis between intermediate products of aromatic components and gene expression, we identified eight genes associated with the linalool, α- and β-ionone biosynthesis pathways. Overall, our study offers valuable genetic resources for sweet osmanthus, while also providing genetic clues for improving the flower color and multi-season flowering of osmanthus and other flowers.

Malus is one of the most widespread genera of Rosaceae and includes several economically and ornamentally significant plants (e.g., apple and crabapple). The extensive genome and transcriptome data for Malus available in public databases offer a great opportunity for phylogenomic, biogeographical, and character evolution analyses in this group. We utilized nuclear genes from 45 transcriptomes/genomes, comprising 32 ingroup taxa (Malus and related species), to reconstruct a comprehensive and well-supported phylogeny and to investigate biogeography and character evolution. Our coalescent-based phylogenies from 12,835 gene families and 1,597 orthologs indicate that Malus encompasses Eriolobus and Docynia, and they identified six well-supported clades within Malus. Malus originated in Northern and Southern East Asia during the early Miocene (~ 20 Ma) and subsequently dispersed to other regions. The persistent calyx in the fruit, lobed leaves, and stone cells represent ancestral traits. A strong phylogenetic signal was detected in three traits: calyx, leaf morphology, and stone cell. Additionally, fruit size showed a significant correlation with calyx morphology. Our findings offer new insights into the phylogeny of Malus, its biogeography, and morphological evolution.

Assessing the current status and identifying the mechanisms threatening endangered plants are significant challenges and fundamental to biodiversity conservation, particularly for protecting Tertiary relict trees and plant species with extremely small populations (PSESP). Ulmus elongata (Ulmus, Ulmaceae) with high values for the ornamental application, is a Tertiary relict tree species and one of the members from PSESP in China. Currently, the wild populations of U. elongata have been threatened by excessive deforestation and urbanization, but limited knowledges of its genetic diversity seriously hinder conservation efforts. Therefore, a further study on the genetic diversity and drivers of genetic pattern in U. elongata is crucial for preserving genetic resources and can serve as a reference for other Tertiary relict plants and PSESP under climate change. Here, a total of 12 populations from 70 individuals of U. elongata were collected covering its geographical distribution in China. Utilizing chloroplast genome datasets, we found that U. elongata exhibited remarkably low nucleotide diversity and gene flow (π = 0.00013, Nm = 0.03). Analysis of molecular variance (AMOVA) showed that genetic variation in U. elongata occurs mainly between eight clades (60.95%). The Mantel tests indicated a significant correlation between genetic differentiation and geographical distances (r = 0.3777, p < 0.05) in U. elongata populations. A notable phylogeographic structure was identified in U. elongata, comprising eight distinct haplogroups (NST = 0.917, GST = 0.876, p < 0.05), which was attributed to the global cooling in the East Asia and Quaternary climate oscillations. Overall, our study using Ulmus elongata as a representative supported the hypothesis that plants belonging to Tertiary relict species and PSESP simultaneously exhibits significantly lower genetic diversity compared to those are either Tertiary relict species or PSESP individually. Furthermore, the low genetic diversity and significant genetic differentiation in U. elongata populations can be primarily ascribed to a combination of factors, including habitat fragmentation resulting from human activities, populations contraction during LGM and small population sizes. This provides a crucial foundation for guiding conservation efforts and implementing management strategies for other Tertiary relict tree species and PSESP. Our findings also provide evidence for the important roles of East Asian monsoon system and climate oscillations in shaping the phylogeographic pattern in subtropical broad-leaved forests.

The colored-leaf Osmanthus fragrans is a valuable ornamental tree species that integrates greenery, colorful leaves, and fragrance. At present, research on colored-leaf Osmanthus fragrans mainly focuses on cultivar breeding, classification and cultivation, and physiological resistance, while studies on leaf color variation remain limited. In this study, the colored-leaf Osmanthus cultivar ‘Jinyu Guihua’ and its female parent were used as materials. The leaf coloration mechanism was systematically investigated through a combined analysis of physiology, transcriptomics, and metabolomics. The results showed that compared with the female parent, the leaves of ‘Jinyu Guihua’ exhibited significantly reduced chlorophyll b and anthocyanin contents, fewer chloroplasts, and more plastoglobules. Transcriptomic analysis identified 3938 differentially expressed genes (DEGs), among which the key chlorophyll metabolism gene CAO was downregulated and NOL was upregulated; the key carotenoid synthesis gene PSY was downregulated and CYP97A3 was upregulated; the key anthocyanin synthesis gene ANS was downregulated; and the PetC2 gene in the photosynthesis-related Cytb6-f complex was upregulated. qRT-PCR validation results were consistent with the RNA-seq data. Metabolomic analysis detected 1290 metabolites, classified into 21 subcategories, with flavonoids being the most abundant (17.21%). Anthocyanin synthase (ANS) significantly downregulated the expression levels of cyanidin-3-O-rutinoside (Cy3R) and delphinidin-3-O-rutinoside (De3R). In conclusion, the leaf color variation in ‘Jinyu Guihua’ is closely related to changes in leaf pigment content and the regulation of key metabolic pathway gene expression. The findings of this study provide a theoretical basis for the molecular breeding of new colored-leaf Osmanthus varieties and serve as a reference for trait research in other ornamental plants.