A comprehensive metabolomics analysis of Torreya grandis nuts with the effective de-astringent treatment during the postharvest ripening stage.

Astringency removal is important for the quality of Torreya grandis nut and occurs after harvest. Here, we evaluated the effect of NaHCO3 treatment on astringency removal and compared the differential metabolites of the seed coat and kernel using a UHPLC QQQ-MS-based metabolomics approach. The result revealed the nut astringency was primarily enriched in the seed coat with more soluble tannins. The NaHCO3 treatment greatly shortened the de-astringency process, as indicated by a faster conversion of soluble tannins to insoluble tannins and more acetaldehyde production. Besides, a total of 293 metabolites, including 92 phenolic acids and 37 flavonoids, were tentatively characterized in the seed coat. A further comparative analysis of the metabolomics indicated epigallocatechin, gallocatechin, catechin, procyanidin B1, B2, B3 and C1 to be the major metabolites influenced by the NaHCO3 treatment. This study provides new insights regarding the metabolite differences of Torreya grandis nuts processed with different de-astringent treatments.

Identification of key genes and enzymes contributing to nutrition conversion of Torreya grandis nuts during post-ripening process.

The seeds of Torreya grandis are necessary to go through a ripening process, which eventually leads to nutrition conversion and the production of edible nuts. However, the molecular basis of nutrition conversion remains unclear. Here, transcriptome sequencing was performed on seeds treated with different temperature and humidity. A total of 881 unigenes related to nutrition conversion were identified. The correlations between nutrient content and gene expression suggested that sucrose phosphate synthase (SPS), dihydrolipoyllysine-residue succinyltransferase component of 2-oxoglutarate dehydrogenase complex (DLST), glycerol-3-phosphate acyltransferase (GPAT) and Pyruvate kinase (PK) may play key roles in nutrition conversion. Transient over-expression of TgDLST, TgPK and TgGPAT in tobacco leaves promoted nutritional conversion. Moreover, enzyme activity analysis indicated that diacylglycerol acyltransferase (DGAT) and pyruvate dehydrogenase (PDH) activities may also accelerate the nutritional conversion. This study uncovers the molecular basis of nutrition conversion in T. grandis seeds, which critical for shortening the time of nutrition conversion.

Acceleration of Aril Cracking by Ethylene in Torreya grandis During Nut Maturation.

Torreya grandis 'Merrillii' is a famous nut with great nutritional value and high medicinal value. Aril cracking is an important process for seed dispersal, which is also an indicator of seed maturation. However, the cracking mechanism of T. grandis aril during the maturation stage remains largely unknown. Here, we provided a comprehensive view of the physiological and molecular levels of aril cracking in T. grandis by systematically analyzing its anatomical structure, physiological parameters, and transcriptomic response during the cracking process. These results showed that the length of both epidermal and parenchymatous cell layers significantly increased from 133 to 144 days after seed protrusion (DASP), followed by a clear separation between parenchymatous cell layers and kernel, which was accompanied by a breakage between epidermal and parenchymatous cell layers. Moreover, analyses of cell wall composition showed that a significant degradation of cellular wall polysaccharides occurred during aril cracking. To examine the global gene expression changes in arils during the cracking process, the transcriptomes (96 and 141 DASP) were analyzed. KEGG pathway analysis of DEGs revealed that 4 of the top 10 enriched pathways were involved in cell wall modification and 2 pathways were related to ethylene biosynthesis and ethylene signal transduction. Furthermore, combining the analysis results of co-expression networks between different transcription factors, cell wall modification genes, and exogenous ethylene treatments suggested that the ethylene signal transcription factors (ERF11 and ERF1A) were involved in aril cracking of T. grandis by regulation of EXP and PME. Our findings provided new insights into the aril cracking trait in T. grandis.