Abstract
Walnut (Juglans regia) is known as a promising woody oil crop with abundant polyunsaturated fatty acids in its kernel. However, the regulation mechanism of walnut oil accumulation and fatty acid metabolism is still poorly understood, which restricted the breeding and genetic improvement of high-quality oil-bearing walnuts. To reveal the molecular mechanism of walnut oil accumulation, considering the potential regulation of microRNA (miRNA) in seed development, in this study, the oil content of walnut kernel on the 80th, 100th and 120th day after flowering (DAF) was tested and the corresponding proportions are 11.51%, 40.40% and 53.20%. Between DAF of 80th~120th, the content of stearic acid and oleic acid tended to increase, but the proportion of other fatty acids tended to decrease. Meanwhile, comparative transcriptome and sRNA-seq analysis on three stages (80th, 100th and 120th DAF), found 204 conserved miRNAs and 554 novel miRNAs in walnut kernels, among which 104 key genes related to walnut oil accumulation were screened. The phospholipid:diacylglycerol acyltransferase metabolic pathway may contribute more to oil accumulation in walnut. 16 miRNA-mRNA regulatory modules related to walnut oil accumulation and fatty acid synthesis were constructed. 8 known miRNAs and 9 novel miRNAs regulate 28 genes involved in fatty acid (FA) metabolism and lipid synthesis. Among them, jre-miRn105, jre-miRn434, jre-miR477d and jre-miR156a.2 are key miRNAs that regulate walnut FA synthesis. Jre-miRn411 and jre-miR399a.1 are closely related to oil accumulation. These data provide new insights and lay the foundation for subsequent studies on walnut FA synthesis and oil accumulation.
Highlights
Juglans regia, a kind of woody oil plant, is commonly known as Persian walnut or English walnut
leafy cotyledon2 (LEC2) can affect the synthesis of FA and TAG by regulating fatty acid desaturase (FAD) 8, FAD7, FAD3, diacylglycerol O-acyltransferase (DGAT), glycerol-3-phosphate acyltransferases (GPAT), lysophosphatidyl acyltransferase (LPAT) and phosphatidic acid phosphatase (PAP) [7]
ABI4 and ABI5 play an important role in regulating diacylglycerol O-acyltransferase 1 (DGAT1) expression, which is an important rate-limiting enzyme in TAG biosynthesis [10,11,12]
Summary
A kind of woody oil plant, is commonly known as Persian walnut or English walnut. ABI4 and ABI5 play an important role in regulating diacylglycerol O-acyltransferase 1 (DGAT1) expression, which is an important rate-limiting enzyme in TAG biosynthesis [10,11,12]. These genes have been studied in soybeans, rapeseed and Arabidopsis, they have not been involved in woody oil crops, especially walnuts. The process of oil accumulation in plants relies on the expression of a variety of lipid biosynthesis genes, which mainly occur at the transcriptional level, as well as complex transcriptional and post-transcriptional control mechanisms [16]. We found some miRNA-mRNA regulatory modules which are potentially related to walnut seed kernel oil accumulation. Our results may provide new insights into the regulatory mechanisms of miRNAs during walnut seed kernel oil accumulation
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