Sapindus mukorossi is a native tree in southern China that has multiple useful functions, including high landscaping, ecological, esthetic, and economic values. More importantly, its fruits are being rapidly developed as raw materials for bioenergy and saponin production in southern China. To provide a standardized phenological description of the species, this study firstly used the BBCH (Biologische Bundesanstalt, Bundessortenamt und CHemische Industrie) scale. In total, eight principal stages—i.e., bud, leaf and shoot development, inflorescence emergence, flowering, fruit development, fruit maturity, senescence and beginning of dormancy—and 58 secondary stages were described. It ranges from vegetative bud dormancy to the onset of the next beginning of the dormancy, using a two-digit numerical coding system. In addition to the descriptions, we provide photographic images of some major developmental stages to standardize morphological characteristics and the phenological observation of S. mukorossi. This study will be an asset for biological researches and cultivation management in Sapindus, and will provide valuable information for other fruit trees.

Longan is an exotic tropical fruit crop and exhibits off‐season flowering induced by potassium chlorate (KClO ₃ ), though the molecular mechanisms remain unclear. We assembled a high‐quality, 441.5 Mb genome of variety ‘Shixia’, with a contig N50 at 28.1 Mb, 29, 325 protein‐coding genes, 26 telomeres and 15 centromeres. Comparative genomic analysis with lychee revealed structural variations potentially driving gene family expansions related to flavone biosynthesis and disease resistance. Transcriptomic profiling showed that natural flowering appears to be primarily regulated by photoperiod, vernalisation and autonomous pathways, while KClO ₃ ‐induced flowering may preferentially activate the gibberellin pathway at 5 days after treatment (DAT) and autonomous pathways at 10 DAT, involving putative repression of DlDDF1 , DlFLCs and DlSVPs , and up‐regulation of DlWRKY75_2 . In the perpetual‐flowering variety ‘Sijimi’, elevated expression of photoperiod genes, such as DlCOR28 , DlCOR27 , DlADO3 , DlPRR5 , DlGI and DlJMJ30 , may explain its perpetual blooming. Overexpression of DlDDF1 in Arabidopsis delayed flowering, partially reversed by KClO ₃ through an increase in bioactive GA ₄ . Together, KClO ₃ ‐induced flowering likely involves oxidative stress response and gibberellin signalling via DlDDF1 repression, while natural flowering relies on seasonal cues. These results lay the foundation for longan genetic improvement.

Biodiesel has many advantages, yet its high price has become the main obstacle to market acceptance. Selecting non-edible woody oil plant resources and optimizing the oil extraction process will contribute to the effective utilization of raw materials and development of the related biodiesel industry. This study presents a detailed evaluation of two Sapindus species (Sapindus delavayi (Franch.) Radlk. and Sapindus mukorossi Gaertn.) as promising feedstocks for biodiesel production. As ultrasonic-assisted extraction (UAE) is considered a green and efficient oil extraction method, the process was optimized by response surface methodology (RSM) using a Box–Behnken design (BBD) in our study. The kernel oil yield of S. delavayi was up to 43.67% ± 0.16% under the optimized extraction conditions (the ultrasonic power was 109W, extracting at 65 °C for 25 min, and the liquid–solid ratio was 9 mL·g⁻¹). The kernel oil yield of S. mukorossi was as high as 45.96% ± 0.21% under the optimized extraction conditions (the ultrasonic power was 114W, extracting at 68 °C for 26 min, and the liquid–solid ratio was 9 mL·g⁻¹). The fatty acid profiles of S. delavayi and S. mukorossi kernel oils showed a high percentage of monounsaturated fatty acids (74.91% and 76.32%, respectively) and a low percentage of polyunsaturated fatty acids (11.11% and 7.83%, respectively) and saturated fatty acids (13.98% and 15.85%, respectively). Most of the properties of the two biodiesels conformed to EN 14214:2014, ASTM D6751–2018 and GB 25199–2017 standards, except for oxidation stability. In general, the results provided the optimized extraction method using ultrasound for the two species oil extraction and proved that the two kernel oils are potentially useful feedstocks for high-quality and low-cost biodiesel production.

Soapberry ( Sapindus mukorossi Gaertn.) pericarps are rich in valuable bioactive triterpenoid saponins. However, the saponin content dynamics and the molecular regulatory network of saponin biosynthesis in soapberry pericarps remain largely unclear. Here, we performed combined metabolite profiling and transcriptome analysis to identify saponin accumulation kinetic patterns, investigate gene networks, and characterize key candidate genes and transcription factors involved in saponin biosynthesis in soapberry pericarps. A total of 54 saponins were tentatively identified, including 25 that were differentially accumulated. Furthermore, 49 genes putatively involved in sapogenin backbone biosynthesis and some candidate genes assumed to be responsible for the backbone modification, including 41 cytochrome P450s and 45 glycosyltransferases, were identified. Saponin-specific clusters/modules were identified by Mfuzz clustering and weighted gene co-expression network analysis, and one TF–gene regulatory network underlying saponin biosynthesis was proposed. The results of yeast one-hybrid assay and electrophoretic mobility shift assay suggested that SmbHLH2, SmTCP4, and SmWRKY27 may play important roles in the triterpenoid saponin biosynthesis by directly regulating the transcription of SmCYP71D-3 in soapberry pericarp. Overall, these findings provide valuable information for understanding the molecular regulatory mechanism of saponin biosynthesis, enriching the gene resources, and guiding further research on triterpenoid saponin accumulation in soapberry pericarps. One–sentence summary: Combining metabolome and transcriptome analysis to identify saponin kinetic patterns, gene networks, and key candidate genes and transcription factors involved in saponin biosynthesis of soapberry.

The phenotypes of Sapindus are significantly influenced by environmental factors, but the responses of oil-related seed phenotypes to environmental factors are still unclear. We sampled 115 seed accessions of Sapindus mukorossi Gaertn. and 33 of Sapindus delavayi (Franch.) Radlk. from fifty-six distinct locations in China to explore the effects of environmental factors on the seed phenotypes. Pearson’s correlation analysis showed that 100-seed kernel weight (SKW), 100-seed shell weight (SSW), and seed kernel content (SKC) were the phenotypes most sensitive to the environmental influence (significantly associated with at least ten environmental factors). Redundancy analysis explained 26.13% of the variance and revealed that longitude was negatively correlated with SKW and SKC but was positively correlated with SSW, whereas elevation had the opposite effect. Monthly sunshine hours was negatively correlated with 100-seed weight and SSW. Additionally, the Mantel test showed that the seed phenotypic variations in Sapindus mukorossi and Sapindus delavayi were significantly affected by environmental factors differently. SKW and SKC of Sapindus delavayi were more sensitive to the influence of key environmental factors and therefore had more potential for oil development. It is recommended to cultivate Sapindus delavayi at lower longitudes to facilitate seed kernel development and promote oil yield. Study Implications: This study revealed the response pattern of the seed phenotypes of Sapindus mukorossi Gaertn. and Sapindus delavay (Franch.) Radlk. to environmental factors. Sapindus delavay had larger seed kernels and thinner seed shells, indicating a higher potential for oil production. At lower longitudes, the seed kernels of Sapindus are heavier, favoring kernel oil production, and the seed shells are lighter, which facilitates processing. This implied that growers can cultivate Sapindus in suitable climatic regions for commercial purposes such as oil production.