Carbohydrates are essential for plant growth and serve as the primary carbon source for lipid biosynthesis in oilseed crops. However, the molecular mechanisms underlying starch degradation and its regulatory network during seed development remain largely unknown, particularly in oil crops such as Torreya grandis. In this study, we systematically characterized the amylase gene family in T. grandis. Through phylogenetic analysis, chromosomal localization, and gene structure examination, we identified 12 amylase genes. Expression profiling across various tissues and seed developmental stages revealed that TgAMY3 was specifically highly expressed in T. grandis seeds, suggesting its crucial role in starch metabolism. Functional analyses demonstrated that TgAMY3 promotes starch degradation, as confirmed by both homologous and heterologous overexpression assays. Moreover, we identified a basic leucine zipper (bZIP) transcription factor, TgbZIP6, as a key regulator of TgAMY3. Yeast one-hybrid and dual-luciferase assays showed that TgbZIP6 directly binds to the TgAMY3 promoter and enhances its transcriptional activity. TgbZIP6 overexpression significantly increased TgAMY3 expression, accelerating starch degradation and promoting subsequent oil accumulation. Our findings establish a regulatory cascade in which TgbZIP6, acting as a transcriptional activator, directly binds to the TgAMY3 promoter to enhance its expression, thereby driving the conversion of starch into lipids during seed development. This study not only elucidates the molecular basis of starch metabolism in T. grandis but also identifies a validated gene regulatory module with potential applications for improving oil yield and quality in other woody oil crops.

Torreya grandis ‘Merrillii’ is a well-known nut in South China with high nutritional value. Severe premature seed abscission limits the industrial development of T. grandis by causing serious economic losses. However, the physiological mechanisms of seed abscission in T. grandis remain poorly understood. To gain insight into the relationships between carbohydrate status and seed abscission, three-year-old seed-bearing branches were taken as representative materials for the entire tree. Furthermore, the time course of changes in the photosynthetic rate and the non-structural carbohydrate (NSC) dynamics were monitored in the main sources (the one-year-old and two-year-old shoots), and the dry weight and NSC levels of sinks (the seeds, current female cone cluster, and current vegetative cluster) across all seed development stages were recorded. The cumulative seed abscission rate significantly increased, reaching 91.5% from 0 to 72 days after seed protrusion time (SPT). NSC levels in the main sources significantly decreased by 56%–79%, accompanied by a significantly increased photosynthesis rate of 17.1%–49.1% during that period and increased NSC levels in the three sinks. The gene expression level of cell wall invertase (TgCWIN) was significantly correlated with sucrose, fructose, and glucose levels. The carbon storage capacity of the main sources significantly decreased from 6.03 to 3.14 mmol C · d⁻¹, with a stable photosynthetic capacity, from 0 to 72 days after SPT, whereas the carbon demand of the three sinks showed a continuously increasing trend from 3.14 to 7.71 mmol C · d⁻¹. In addition, sucrose supplementation significantly decreased the cumulative seed abscission rate. These results suggest that storage carbohydrates play a major role in the regulatory mechanism of seed abscission in T. grandis. Our study provides a theoretical basis for improving T. grandis yield through establishing a better carbon balance between sources and sinks using timely fertilization or proper pruning procedures.

Torreya grandis is a characteristic rare economic tree species in subtropical mountainous areas. The nut has a variety of bioactive compounds, such as polyphenols and vitamins. However, the carotenoids compositions and its regulatory mechanisms underlying carotenoid biosynthesis in kernels remain unknown. Here, the major carotenoids in the kernel were analyzed. The result showed that lutein and β-carotene were the predominant carotenoids in the kernel, while low levels of α-carotenoid and zeaxanthin were detected. Lutein and β-carotene were decreased during the maturation of kernel. Expression analysis by RNA-seq and qRT-PCR indicated that the expressions of TgCYP97A3 and TgLCYB were also reduced during the maturation of kernel. The contents of lutein or β-carotene were obviously increased in tobacco transiently overexpressing TgCYP97A3 or TgLCYB. Moreover, DPPH radical scavenging activity and FRAP were also significantly enhanced. In addition, several MYB and WRKY transcription factors TgMYBS3, TgMYB48 and TgWRKY11 were identified to positively regulate the TgCYP97A3 expression, while TgMYB48, TgWRKY2 and TgWRKY11 could upregulate the TgLCYB expression. The illustration of carotenoids biosynthesis and its molecular mechanism in kernels not only provides a basis for understanding carotenoids biosynthesis in kernels, but also enables the use of molecular biotechnology to develop new health products rich in carotenoids based on T. grandis nuts.