Transcriptome Analysis of Genes Involved in Fatty Acid and Lipid Biosynthesis in Developing Walnut (Juglans regia L.) Seed Kernels from Qinghai Plateau

Abstract

Walnut (Juglans regia) is an important woody oil-bearing plant with high nutritional value. For better understanding of the underlying molecular mechanisms of its oil accumulation in the Qinghai Plateau, in this study we monitored walnut fruit development, and 15 cDNA libraries were constructed from walnut seed kernels collected at 72, 79, 93, 118 and 135 days after flowering (DAF). The candidate genes were identified using sequencing and expression analysis. The results showed that the oil content in the kernels increased dramatically in late July and reached the maximum value of 69% in mature seed. More than 90% of the oils were unsaturated fatty acids (UFAs) and linoleic acid (18:2) was the predominant UFA accumulated in mature seed. Differentially expressed genes (DEGs) in 15 KEGG pathways of lipid metabolism were detected. We identified 119 DEGs related to FA de novo biosynthesis (38 DEGs), FA elongation and desaturation (39 DEGs), triacylglycerol (TAG) assembly (24 DEGs), oil bodies (12 DEGs), and transcription factors (TFs, 6 DEGs). The abundantly expressed oleosins, caleosins and steroleosins may be important for timely energy reserve in oil bodies. Weighted gene coexpression network analysis (WGCNA) showed that AP2/ERF and bHLH were the key TFs, and were co-expressed with ACC1, α-CT, BCCP, MAT, KASII, LACS, FATA, and PDCT. Our transcriptome data will enrich public databases and provide new insights into functional genes related to the seed kernel lipid metabolism and oil accumulation in J. regia.

Integrated metabolomic and transcriptomic dynamic profiles of endopleura coloration during fruit maturation in three walnut cultivars

“…Endopleura color is a vital factor for determining the economic value and aesthetic appeal of nuts and in crop breeding. Very little systematic analyses of endopleura color have been carried out in woody crops [ 19 , 26 ]. Walnuts ( Juglans ) are a key ebible nut that are high in proteins, amino acids, lipids, and carbohydrates, as well as a variety of trace elements and minerals [ 20 , 25 ].…”

“…Walnuts are a typical food that can be used as a medicine as well as food; it is a medicine listed in the Chinese Pharmacopoeia [ 21 – 25 ]. Its medicinal efficacy is mostly related to the rich polyphenol and flavonoid components, which have antioxidant and immunity-enhancing effects, and has been a hotspot for research and development in recent years [ 26 – 28 ]. The walnut kernel consists of the embryo (seed kernel or kernel) and the endopleura (seed coat, kernel membrane), the walnut endopleura is wrapped in a layer of film on the surface of the kernel [ 29 , 30 ].…”

“…Flavonoids, as secondary metabolites in plants, belong to a class of polyphenolic compounds [ 47 – 50 ]. Flavonoids can be detected in nearly every variety of fruits, vegetables, and other agricultural produce [ 26 , 51 ]. In addition, various nutritional products contain flavonoids as essential ingredients.…”

Metabolomics and Transcriptomics Provide Insights into Lipid Biosynthesis in the Embryos of Walnut (Juglans regia L.)

“…The synthesis of vegetable oil mainly involves the synthesis of fatty acids in the plastids and the synthesis of TAGs in the endoplasmic reticulum. Shi et al [ 8 ] have shown that there were five kinds of main fatty acids in the mature walnut seeds: palmitic acid (16:0), stearic acid (18:0), oleic acid (18:1), linoleic acid (18:2), and linolenic acid (18:3). During the period of oil rapid accumulation, the content of saturated fatty acids decreased rapidly, while the content of unsaturated fatty acids increased rapidly [ 9 ].…”

“…A total of 28 genes related to walnut oil biosynthesis were screened out, corresponding to 17 differential expression miRNAs. Huang et al [ 23 ] and Shi et al [ 8 ] have sequenced transcriptomes during walnut seed kernel development, which increases the available transcriptome data for walnut seed kernels’ lipid metabolism. Recently, walnut genome assembly at the chromosome level was published, which will be more conducive to walnut transcriptome research [ 24 ].…”