Critical metabolic pathways and SAD/FADs, WRI1s, and DGATs cooperate for high-oleic acid oil production in developing oil tea (Camellia oleifera) seeds

Abstract

Oil tea trees produce high-quality edible oils with desirably high oleic acid (18:1) and low linoleic (18:2) and linolenic (18:3) fatty acid (FA) levels, but the limited understanding of tea oil biosynthesis and regulation has become a significant obstacle for breeding of high-yield and quality oil tea varieties. By integrating metabolite and transcriptome analyses of the developing oil tea seeds, we dissected the critical metabolic pathways including glycolysis, fatty acid and triacylglycerol (TAG) biosynthesis, as well as genes essential for tea seed oil production. Two plastidic stearoyl-ACP desaturases (CoSAD1 and 2) and two ER-localized FA deasturases (CoFAD2 and 3) were functionally characterized responsible for high-18:1 and low-18:2 and-18:3 proportions in tea oils. Two diacylglycerols O-acyltransferases (CoDGAT1 and 2) that may prefer to synthesize 18:1-TAG were functionally characterized and might be also important for high 18:1-TAG production. The highly expressed CoWRI1a and b were identified and characterized as activators of glycolysis and regulators of directing source carbon flux into FA biosynthesis in developing oil tea seeds. The up-regulated CoSADs with down-regulated CoFAD2 and CoFAD3 at the late seed developmental stages mainly accounted for high 18:1 level. Two CoDGATs might be responsible for assembling TAGs with oleoyl acyl chains, whilst two CoWRI1s regulated carbons from parental sources partitioning into oil production in oil tea embryo sinks. This study provides a deep understanding of the biosynthesis of tea seed oils and information of genes that may be used as molecular markers to breed oil tea varieties with higher oil yield and quality.

Transcriptome and Anatomical Comparisons Reveal the Effects of Methyl Jasmonate on the Seed Development of Camellia oleifera

“…Importantly, stearoyl-[acyl-carrier-protein] 9-desaturase (SAD) and ω-fatty acid desaturase (FAD) are responsible for the formation of various fatty acids in oilseed plants. 2,61 In the present study, SAD6-1, SAD6-2, and FAD2-3 were highly expressed in the late stage of seed development, and SAD6-1 and SAD6-2 levels were enhanced by more than 90% in MeJA-treated seeds at 334 DAP relative to control (Figure 5B), which exhibited positive correlations with the relative increase in the content of oil, oleic acid, and unsaturated fatty acids (Table S7).…”

“…The transcript expression levels of the biotin carboxyl carrier protein of acetyl-CoA carboxylase 2 ( BCCP2 ) increased with seed maturity, exhibited a 0.59-fold increase in MeJA-treated seeds at seed maturity (Figure B), and were further validated using qRT-PCR (Figure S5). Importantly, stearoyl-[acyl-carrier-protein] 9-desaturase (SAD) and ω-fatty acid desaturase (FAD) are responsible for the formation of various fatty acids in oilseed plants. , In the present study, SAD6 -1, SAD6 -2, and FAD2-3 were highly expressed in the late stage of seed development, and SAD6 -1 and SAD6 -2 levels were enhanced by more than 90% in MeJA-treated seeds at 334 DAP relative to control (Figure B), which exhibited positive correlations with the relative increase in the content of oil, oleic acid, and unsaturated fatty acids (Table S7). According to the qRT-PCR result, the expression level of FAD2-3 was down-regulated about 56.41% at 334 DAP under MeJA treatment compared with the control, respectively (Figure C).…”

“…Furthermore, Camellia oil is recommended by the Food and Agriculture Organization of the United Nations as a high-quality edible oil due to its health-promoting effects on reducing the cholesterol, treating cardiovascular and cerebrovascular diseases, improving the immunity, and scavenging free radicals. , In 2021, the annual production of Camellia oil exceeded 0.9 million tons, and its annual output value exceeded 1920 billion yuan with an expanding trend, ranking the top 10 in the total consumption of edible oils in China . In view of the increasing market requirement for high-quality Camellia oil, investigations of oil accumulation and fatty acid biosynthesis in Camellia oil have been carried out. ,− However, up to 70% of the Camellia oil planting area is low-seed-yield forests, which substantially restricts the extensive development of the Camellia oil industrial sector …”

“…oleifera seeds, mainly contains monounsaturated, polyunsaturated, and minor saturated fatty acids . Among them, unsaturated fatty acids approximately account for 90% of the total fatty acids, comprising ∼80% oleic acid and ∼7% linoleic acid, the proportion of which is comparable to that of olive oil . Furthermore, Camellia oil is recommended by the Food and Agriculture Organization of the United Nations as a high-quality edible oil due to its health-promoting effects on reducing the cholesterol, treating cardiovascular and cerebrovascular diseases, improving the immunity, and scavenging free radicals. , In 2021, the annual production of Camellia oil exceeded 0.9 million tons, and its annual output value exceeded 1920 billion yuan with an expanding trend, ranking the top 10 in the total consumption of edible oils in China .…”

Maturity Grading and Identification of Camellia oleifera Fruit Based on Unsupervised Image Clustering

“…For a long time, the oil content has been considered one of the most critical parameters to determine the quality of Camellia oleifera , which can be applied as a stable and climate-independent parameter to determine the Camellia oleifera fruit maturity stages [ 18 , 19 , 20 ]. Based on literature studies, Camellia oleifera has an oil content that will significantly increase after entering maturity, and then it will slowly decrease due to being overripe [ 21 ].…”