Transcriptomic and Metabolic Analyses Elucidate the Metabolomic Variation in Leaf Development of a Calcium-Rich Vegetable (Primulina eburnea)

Primulina eburnea, a plant with a longstanding history of traditional medicinal use, has emerged as a novel calcium-rich vegetable characterized by a remarkable abundance of soluble and bioavailable calcium within its leaves. However, most of the metabolites produced by P. eburnea have not been identified, and few studies have addressed the accumulation of nutritional and medicinal ingredients during leaf development. In the present study, we investigated the "Gaogai-1" cultivar by integrating transcriptomic and mestabolomic methods. A total of 1041 metabolites were identified in calcium-rich vegetable leaves. During leaf development, most of the flavor components, including amino acids and derivatives, organic acids and derivatives, and carbohydrates, decreased their content, which contrasted with the starch content. Most of the antioxidant components, e.g., flavonoids, alkaloids, vitamins, and phenolamines, were more highly accumulated in the bud leaves than in the mature leaves, but terpenes had the opposite trend. These results indicate that leaves of different developmental stages are suitable for different medicinal uses and that P. eburnea could be regarded as a new type of medicinal and edible vegetable. Furthermore, most of the coding genes related to the important components that influence the flavor and nutritional and medicinal values were identified, and their expressions were consistent with the component accumulation profiles. Transcription factors that may regulate the coding genes were identified by combining the co-expression network and cis-element binding ability prediction. The high level of water-soluble calcium was maintained by the high expression of Ca2+/cation antiporter genes in calcium-rich vegetable leaves. Our results uncovered metabolomic and molecular evidence of the mechanisms of nutritional and medicinal component accumulation underlying the leaf development of a calcium-rich vegetable. This study provides a wealth of data for the future utilization and improvement of calcium-rich vegetable cultivars.