Jojoba oil, a natural substance, is a kind of raw material favored by cosmetics. However, few people know that Jojoba's Latin name is "China". In fact, China began to introduce Jojoba sporadically in 1970s, and almost no large-scale cultivation was carried out. This naming is due to the fact that the seeds of Jojoba collected by the discoverer from an American botanical garden in the early19th century are confused with another seed collected in China.
Comparison between Jojoba seeds and other crop seeds
However, the historical relationship between Jojoba and China may be rewritten by scientists in China.
Recently, Science-Progress published the high-quality reference genome of Jojoba, an oil crop, which was jointly completed by rape team and bioinformatics team of Huazhong Agricultural University and five foreign units, and analyzed the synthetic pathway of wax esters in Jojoba seeds. Scientists believe that it is no longer a dream to synthesize jojoba oil from oilseeds such as rape in southern China.
"Liquid gold" is in short supply.
The price of high quality jojoba oil is $58 per kilogram. There are no other natural substitutes and no efficient synthetic methods. However, the global output is 50 times different from the expected demand, so jojoba oil is called "liquid gold".
"Jojoba oil, which is native to desert areas in the United States, is very special. It is actually a liquid wax ester. " Guo Liang, the correspondent of the paper and a professor at Huazhong Agricultural University, told the China Journal of Science that this liquid paraffin is composed of fatty alcohols and esters of fatty acids, and its carbon chain length is C20-C24, which is unique in the plant kingdom. In the animal kingdom, only sperm whale fish oil is similar.
"Jojoba is the only known oil plant that can synthesize liquid wax ester." Guo Liang introduced that pure Jojoba oil has the characteristics of strong antioxidant capacity and strong permeability, and its structure is similar to human sebum, which is easy to be absorbed by the skin, not greasy, and can promote the maintenance of skin moisture.
Previous studies have shown that the composition and structure of jojoba oil will not change obviously with the change of planting location, soil type, rainfall or altitude, and it is not easy to deteriorate after long-term storage after harvest. It is very stable at high temperature and high pressure, so it is widely used in mechanical lubrication, defoaming, wear resistance, rust prevention and oxidation resistance.
However, due to the complex synthesis process, harsh conditions and low yield, especially the high cost of synthesizing ultra-long chain fatty alcohols, there is no artificial product of jojoba oil at present.
The original meaning of Jojoba is "magic shrub", and it is also called "the gospel of saving arid areas". The research shows that even if it doesn't rain in the desert 1 year, mature jojoba trees can still survive. Generally speaking, the life span of jojoba trees is about 200 years. Although Jojoba is very resistant to high temperature and drought, its seedlings do not like drought, and it is difficult to ensure the survival rate of afforestation without artificial irrigation in the early stage of afforestation.
Mao Xinwei, a researcher at the Institute of Forest Chemistry of the Chinese Academy of Forestry, once wrote that Jojoba is naturally distributed in the Sonora Desert in North America. At present, it has been commercialized in the United States, Israel, Peru, Argentina, Australia and India. It is estimated that when the global planting area reaches 2.833 million hectares, Jojoba oil can initially meet the current consumption demand.
197 1 year, after the international whaling commission issued a whaling ban, jojoba oil attracted much attention. Guo Liang told reporters that due to the long growth cycle of Jojoba, female plants only account for about 20% of the natural population, and high-quality Jojoba oil generally comes from desert areas, which leads to the slow development of Jojoba industry. In addition, the low oil yield of conventional mechanical pressing has a certain impact on its industry.
"Although the global output of Jojoba oil has increased from 500 tons in 1986 to 4,000 tons in 20 12, there is a huge gap with the expected annual consumption of Jojoba oil of about 200,000 tons. Therefore, the shortage of jojoba oil and its commercial and industrial value have led to its high price. " Guo Liang said.
In China, the introduction of Jojoba began in the late 1970s and basically ended in the 1990s. However, this oil crop named "Zhonghua" has not been studied in China, and the asexual propagation cutting technology has not been completely broken through, which has not yet produced economic benefits.
Unique synthetic route
In the past ten years, scientists have synthesized jojoba wax ester from oilseeds such as rape and flax mustard by genetic engineering. The wax ester content accumulated in these oilseeds is low, and the seed germination rate is low. However, in Jojoba seeds, wax esters account for more than 95% of the total oil content, and the seeds can still germinate normally, which implies that there is a special mechanism for the synthesis, storage and degradation of wax esters in Jojoba seeds.
"What we have obtained this time is a high-quality reference genome at the chromosome level and the first Jojoba genome map in the world." Guo Liang told China Science Journal that the lack of reference genomes limited the analysis of the mechanism of wax ester synthesis in Jojoba seeds.
Genome Map of Hojoba Photo courtesy of Huanong University
Paper correspondent Chen Lingling, a professor at Huazhong Agricultural University, introduced that they used PacBio, Illumina and Hi-C sequencing to assemble a reference genome of Jojoba with a size of 887 Mb and a Contig N50 of 5.2 Mb, and annotated 23,490 genes encoding protein.
Subsequently, the team began to analyze the mechanism of wax ester synthesis.
Chen Lingling introduced that the content of wax esters in Jojoba seeds is about 50% of the dry weight of seeds, which provides energy and carbon source for seed germination. The synthesis of wax ester is mainly to reduce fatty acyl-CoA to fatty alcohol by fatty acyl-CoA reductase FAR. Then, under the action of wax ester synthase WS, fatty alcohol and fatty acyl-CoA were esterified to produce wax ester.
Many microorganisms, such as Acinetobacter, euglena and deep-sea algae, can also synthesize wax fat in cells. But the carbon chain length of jojoba wax ester is different from theirs, and its function is also different. This may be due to the different substrate preferences of different species for FAR and WS. "Guo Liang told China Science Journal.
They analyzed the distribution of lipids in Jojoba seeds. The results showed that wax esters were mainly concentrated in the cotyledons of seeds, while little triacylglycerol was mainly concentrated in the hypocotyls of seeds. Transcriptome analysis of different parts of seeds showed that the expression levels of fatty acyl-CoA elongase 1, fatty acid reductase and wax ester synthase genes involved in wax ester synthesis in cotyledons were much higher than those in hypocotyls. At the same time, the expression of diacylglycerol acyltransferase in cotyledons is much lower than that in hypocotyls.
The spatial distribution map of lipid molecules in Jojoba seeds was provided by Huanong University.
"Genes encoding protein related to fatty acid synthesis and oil storage are often highly expressed in cotyledons. The difference in spatial expression of these genes may be the main reason for the obvious difference in the distribution of wax esters and triacylglycerol in Jojoba seeds. " Chen Lingling said.
"These studies have enabled us to have a deeper understanding of the synthesis mechanism of Jojoba wax ester and provided theoretical basis for the improvement of Jojoba varieties." Kelvin Cui, a researcher at the Institute of Agricultural Genome of China Academy of Agricultural Sciences, told China Science Journal.
Using rape to "borrow a baby"
The high price of jojoba oil seriously limits its application range, and it is only used in some medicines and cosmetics. Guo Liang introduced that at present, a large number of wax esters on the market are mainly obtained through chemical synthesis or biotechnology based on lipase. However, these fatty alcohols must be obtained by chemical synthesis, which leads to their high cost.
Therefore, "how to produce cheap similar jojoba wax ester is increasingly urgent." Guo Liang explained that it is the first choice to synthesize a large number of wax esters similar to jojoba oil in organisms through genetic engineering and metabolic engineering.
Scientists have synthesized wax esters similar to jojoba oil from Arabidopsis thaliana and flax seeds under laboratory conditions. However, the success rate of seed germination of its offspring is not ideal.
Rape, as the largest vegetable oil production crop in China, has accumulated rich germplasm resources since its introduction and domestication in the middle of last century. With the changes of planting methods and rural labor structure and the influence of rapeseed oil economic benefits, the benefits of rapeseed planting in China have decreased year by year.
Guo Liang thinks that the fatty acid composition in high erucic rape seeds accords with the substrate preference of FAR and WS in Jojoba, which makes it possible to synthesize Jojoba oil in high erucic rape seeds. Synthesizing a large amount of jojoba oil in rape seeds can not only reduce the cost of jojoba oil in the current market, but also improve the benefit of rape planting.
Analysis of storage mechanism of liquid wax ester in synthetic Jojoba seeds
The advent of high-quality genome and the announcement of wax synthesis mechanism will help scientists solve some key scientific problems of wax ester synthesis in rapeseed.
In addition, Kelvin Cui believes that the biggest problem facing Jojoba cultivation at present is the variability of male and female plants, and the ratio of male and female plants varies greatly. Due to the low proportion of female plants and the low input-output ratio of growers, the development of Jojoba planting industry is seriously limited. The publication of Jojoba genome sequence provides a basis for solving the problem of female plant screening.
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