Transcriptome and Metabolome Based Mechanisms Revealing\nthe Accumulation and Transformation of Sugars and Fats in Pinus armandii Seed Kernels during the Harvesting\nPeriod

Pinus armandii seed kernel\nis a\nnutrient-rich and widely consumed nut whose yield and quality are\naffected by, among other things, harvesting time and climatic conditions,\nwhich reduce economic benefits. To investigate the optimal harvesting\nperiod of P. armandii seed kernels,\nthis study determined the nutrient composition and seed kernel morphology\nand analyzed the gene expression and metabolic differences of P. armandii seed kernels during the harvesting period\nby transcriptomics and metabolomics. The results revealed that during\nthe maturation of P. armandii seed\nkernels, there was a significant increase in the width, thickness,\nand weight of the seed kernels, as well as a significant accumulation\nof sucrose, soluble sugars, proteins, starch, flavonoids, and polyphenols\nand a significant decrease in lipid content. In addition, transcriptomic\nand metabolomic analyses of P. armandii seed kernels during the harvesting period screened and identified\n103 differential metabolites (DEMs) and 8899 differential genes (DEGs).\nAnalysis of these DEMs and DEGs revealed that P. armandii seed kernel harvesting exhibited gene–metabolite differences\nin sugar- and lipid-related pathways. Among them, starch and sucrose\nmetabolism, glycolysis, and gluconeogenesis were associated with the\nsynthesis and catabolism of sugars, whereas fatty acid degradation,\nglyoxylate and dicarboxylic acid metabolism, and glycerophospholipid\nmetabolism were associated with the synthesis and catabolism of lipids.\nTherefore, the present study hypothesized that these differences in\ngenes and metabolites exhibited during the harvesting period of P. armandii seed kernels might be related to the\naccumulation and transformation of sugars and lipids. This study may\nprovide a theoretical basis for determining the optimal harvesting\ntime of P. armandii seed kernels, changes\nin the molecular mechanisms of nutrient accumulation, and quality\ndirected breeding.