Polyploid breeding is one of the important ways to create new varieties of forest trees and cultivate excellent germplasm. This article systematically reviewed recent advances in the induction of polyploidy in forest trees using physical, chemical, and biological methods both domestically and internationally. The physical method is represented by temperature change and mechanical damage, which is easy to operate, but has the problems of low induction rate and poor controllability. Colchicine treatment, as the representative of chemical methods, is the most mature and widely used method. It is the mainstream method for polyploid creation of forest trees. However, high chimerism incidence and prolonged recovery time post-treatment remain major drawbacks. Biological methods such as protoplast fusion and endosperm culture have developed rapidly in recent years, showing unique advantages in overcoming distant incompatibility and reproductive isolation and shortening the breeding cycle. At present, the research on polyploid breeding of forest trees mainly focuses on representative tree species such as poplar and eucalyptus, and homologous tetraploid and triploid plants have been successfully obtained through various methods. Polyploid plants exhibit giant organs, significantly improved fiber length and wood properties, as well as enhanced stress resistance. In the future, the collaborative application mode of the three methods should be further optimized, and the application potential of emerging technologies such as gene editing in polyploid creation should be actively explored to promote the development of forest polyploid breeding in the direction of high efficiency and precision.

Wintersweet (Chimonanthus praecox), a well-known fragrant flowering shrub, is extensively planted for ornamental purpose and production of floral essential oil. Although the tepal color of wintersweet varieties exhibits the most remarkable diversity, variations in the floral scent traits are also noticeable across different cultivars. In this study, the floral volatile organic compounds (VOCs) in three wintersweet cultivars, ‘Yanlingsuxin’, ‘Yuxiang’, and ‘Hongyun’ were detected via GC–MS coupled with OAV. The distinct floral aromas of the three cultivars were primarily attributed to benzyl alcohol (abundant in ‘Yuxiang’), linalool (abundant in ‘Yanlingsuxin’), (−)-γ-cadinene and eugenol (abundant in ‘Hongyun’). Integrated analyses of metabolome and transcriptome showed that an R2R3-MYB transcription factor gene, CpODO1, potentially have a crucial regulatory function in controlling the production of multiple aroma compounds. Overexpression of CpODO1 can enhance the production of benzyl alcohol in transgenic tobacco flowers. Analysis of DAP-seq data, EMSA and dual-luciferase assay revealed that CpODO1 predominantly regulate the expression of CpCYP71, a cytochrome P450 gene encoding a key enzyme in the production of benzyl alcohol, and the transcriptional regulation of CpODO1 is driven by CpEOBII. The identification of polymorphisms in the MYB binding cis-motifs of CpCYP71 and CpODO1 promoters revealed the regulatory mechanism underlying the varied synthesis of benzyl alcohol in three wintersweet cultivars. This study provides new anchor points for floral scent quality improvement breeding of wintersweet, and the profusion of wintersweet germplasm can serve as a material basis for developing various aroma products.

The mu oil tree (Vernicia montana Lour.) is a dioecious species, but the genetic mechanisms underlying its phenotypic sexual dimorphism are unclear. In this study, we determined two pivotal phases of sex differentiation of mu oil tree via morphological and histological analyses of unisexual flowers: (Ⅰ) differentiation of male or female primordia to produce staminate flowers (SFs) or transient hermaphrodite flowers (HFs), and (Ⅱ) complete abortion of stamens in transient HFs to generate pistillate flowers (PFs). A total of 1621 sex-biased genes were identified by comparative transcriptome analysis which exhibited elevated rates of protein evolution than unbiased genes. The female-biased genes were enriched in the production of defense compounds while male-biased genes were focused on the production of viable pollens. Transcriptome-based analysis revealed that the differentially expressed genes (DEGs) between PFs and SFs in phase I involved in abscisic acid (ABA), auxin (AUX), cytokinin (CK), ethylene (ET), and gibberellin (GA) biosynthesis and signaling showed higher expression levels in males than in females in general, whereas the DEGs involved in jasmonic acid (JA) and salicylic acid (SA) pathways displayed opposite expression patterns. Moreover, differentially expressed endogenous ABA, AUX, GAs, JA, and SA exhibited consistent biased expression patterns with the DEGs by UPLC-MS-based analysis. Exogenous application of an anti-ethylene plant growth regulator could promote the development of stamens in PFs and generated HFs. Comparative transcriptomic and hormonal analyses of PFs and SFs in phase Ⅱ indicated an increase in ET concentration when abortion of stamens in PFs occurred. This study suggested that phytohormones play key roles in sex dimorphism and ET may determine the development of stamens in PFs of mu oil tree, which provides an insight into plant sex differentiation mechanisms.