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Peanuts with high oleic acid content are usually considered to be beneficial for human health and edible oil storage. In breeding practice, peanut lines with high monounsaturated fatty acids are selected using fatty acid desaturase 2 (FAD2), which is responsible for the conversion of oleic acid (C18:1) to linoleic acid (C18:2). Here, comparative transcriptomics were used to analyze the global gene expression profile of high- and normal-oleic peanut cultivars at six time points during seed development. First, the mutant type of FAD2 was determined in the high-oleic peanut (H176). The result suggested that early translation termination occurred simultaneously in the coding sequence of FAD2-A and FAD2-B, and the cultivar H176 is capable of utilizing a potential germplasm resource for future high-oleic peanut breeding. Furthermore, transcriptomic analysis identified 74 differentially expressed genes (DEGs) involved in lipid metabolism in high-oleic peanut seed, of which five DEGs encoded the fatty acid desaturase. Aradu.XM2MR belonged to the homologous gene of stearoyl-ACP (acyl carrier protein) desaturase 2 (SAD2) that converted the C18:0 into C18:1. Further subcellular localization studies indicated that FAD2 was located at the endoplasmic reticulum (ER), and Aradu.XM2MR was targeted to the plastid in Arabidopsis protoplast cells. To examine the dynamic mechanism of this finding, we focused on the peroxidase (POD)-mediated fatty acid (FA) degradation pathway. The fad2 mutant significantly increased the POD activity and H2O2 concentration at the early stage of seed development, implying that redox signaling likely acted as a messenger to connect the signaling transduction between the high-oleic content and Aradu.XM2MR transcription level. Taken together, transcriptome analysis revealed the feedback mechanism of SAD2 (Aradu.XM2MR) associated with FAD2 mutation during the seed developmental stage, which could provide a potential peanut breeding strategy based on identified candidate genes to improve the content of oleic acid.

Peanuts (Arachis hypogaea L.) are an important oilseed crop, containing high contents of protein and fatty acids (FA). The major components of FA found in peanut oil are unsaturated FAs, including oleic acid (OA, C18:1) and linoleic acid (LOA, C18:2). Moreover, the high content of OA in peanut oil is beneficial for human health and long-term storage due to its antioxidant activity. However, the dynamic changes in proteomics related to OA accumulation during seed development still remain largely unexplored. In the present study, a comparative proteome analysis based on iTRAQ (isobaric Tags for Relative and Absolute Quantification) was performed to identify the critical candidate factors involved in OA formation. A total of 389 differentially expressed proteins (DEPs) were identified between high-oleate cultivar Kainong176 and low-oleate cultivar Kainong70. Among these DEPs, 201 and 188 proteins were upregulated and downregulated, respectively. In addition, these DEPs were categorized into biosynthesis pathways of unsaturated FAs at the early stage during the high-oleic peanut seed development, and several DEPs involved in lipid oxidation pathway were found at the stage of seed maturation. Meanwhile, 28 DEPs were sporadically distributed in distinct stages of seed formation, and their molecular functions were directly correlated to FA biosynthesis and degradation. Fortunately, the expression of FAB2 (stearoyl-acyl carrier protein desaturase), the rate-limiting enzyme in the upstream biosynthesis process of OA, was significantly increased in the early stage and then decreased in the late stage of seed development in the high-oleate cultivar Kainong176. Furthermore, real-time PCR verified the expression pattern of FAB2 at the mRNA level, which was consistent with its protein abundance. However, opposite results were found for the low-oleate cultivar Kainong70. Overall, the comparative proteome analysis provided valuable insight into the molecular dynamics of OA accumulation during peanut seed development.