Toona sinensis is an important “vegetable and timber” tree species that is widely distributed in eastern and southeastern Asia. An efficient mechanism for preserving and utilizing germplasm resources is crucial for speeding up the process of genetic improvement of T. sinensis. We collected a total of 1040 germplasm resources of T. sinensis from China, Britain, and New Zealand. Using a total of 27,040 markers, we analyzed the genetic diversity, genetic structure, and core collection of these resources. Additionally, a comprehensive evaluation method for phenotypes of T. sinensis was established by principal component analysis (PCA) and the technique for order preference by similarity to ideal solution (TOPSIS). Our analysis included three main results: Firstly, the breeding population, consisting of a total of 1040 individuals, contains a diverse genetic pool and can be divided into two genetic clusters. Secondly, the best core collection was obtained from the alternative population, consisting of a total of 208 individuals and comprising 20% of the breeding population. It was screened out based on Core Hunter 3 software with the average entry-to-nearest-entry (E-NE) algorithm. Finally, a comprehensive evaluation method was established based on eight selected agronomic traits of the core collection. This method allowed us to screen the best individual plants of the core collection, including N0237, N0972, and N0409. Overall, our research findings will enable better preservation and utilization of T. sinensis germplasm resources and result in faster improvement of T. sinensis varieties.

Toona sinensis, commonly known as Chinese Toon, is a plant species that possesses noteworthy value as a tree and vegetable. Its tender young buds exhibit a diverse range of colors, primarily determined by the presence and composition of anthocyanins and flavonoids. However, the underlying mechanisms of anthocyanin biosynthesis in Toona sinensis have been rarely reported. To explore the related genes and metabolites associated with composition of leaf color, we conducted an analysis of the transcriptome and metabolome of five distinct Toona clones. The results showed that differentially expressed genes and metabolites involved in anthocyanin biosynthesis pathway were mainly enriched. A conjoint analysis of transcripts and metabolites was carried out in JFC (red) and LFC (green), resulting in the identification of 510 genes and 23 anthocyanin-related metabolites with a positive correlation coefficient greater than 0.8. Among these genes and metabolites, 23 transcription factors and phytohormone-related genes showed strong coefficients with 13 anthocyanin derivates, which mainly belonged to the stable types of delphinidin, cyanidin, peonidin. The core derivative was found to be Cyanidin-3-O-arabinoside, which was present in JFC at 520.93 times the abundance compared to LFC. Additionally, the regulatory network and relative expression levels of genes revealed that the structural genes DFR, ANS, and UFGT1 might be directly or indirectly regulated by the transcription factors SOC1 (MADS-box), CPC (MYB), and bHLH162 (bHLH) to control the accumulation of anthocyanin. The expression of these genes was significantly higher in red clones compared to green clones. Furthermore, RNA-seq results accurately reflected the true expression levels of genes. Overall, this study provides a foundation for future research aimed at manipulating anthocyanin biosynthesis to improve plant coloration or to derive human health benefits.

As a special woody vegetable, Chinese toon (Toona sinensis) has a unique flavor, which is mainly formed by a combination of volatile substances. The secretion and storage of volatile odorants in plants are often carried out in trichomes. Currently, studies on the formation of T. sinensis flavor in terms of biosynthetic processes and epidermal trichome morphology are scarce. Here, we conducted a detailed analysis of the morphology, structure, and distribution of trichomes on the leaves of T. sinensis. We identified three types of trichomes: non-glandular, sessile glandular, and stalked glandular. We found that the distribution of trichomes varies greatly in the natural populations of T. sinensis, and this may be closely related to the changes in volatile components. In order to clarify the relationship between secondary metabolism and trichome formation, we integrated the metabolic analysis of volatiles with transcriptome analysis and discovered two important (Terpene Synthase) TPS genes that may be directly involved in terpene synthesis. Through the heterologous expression in tobacco and the transient expression in T. sinensis, we showed that the TPS genes can participate in the synthesis of sesquiterpenes, among which TsTPS1262 can lead to the synthesis of elemene in T. sinensis. Our study provides insights into the synthesis pathways of complex volatile components in T. sinensis and also provides a basis for flavor breeding applications.