The size of the coconut tree was decided 4 million years ago

Green Dwarf Coconut Photo courtesy of interviewee

Coconut is an important tropical oil and fruit crop.
It has rich traits, such as tall or short plants, more or less coconut meat, large or small coconut husks.
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What causes these differences? There are too many mysteries to be solved in the coconut
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Recently, in a paper published in Genome Biology , the scientific research team mapped the high-quality reference genome of tall and short coconuts, revealed the evolutionary process of monocot chromosomes, and analyzed the high and short species.
The genetic basis for the difference in key traits such as plant height and fiber content of coconuts, and the discovery of the key "switch" to control height, decrypted the coconut "green revolution" that occurred about 4 million years ago
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Mapping high-quality reference genomes

Coconut is one of the important economic crops in Hainan.
As of 2020, the province’s coconut groves cover an area of ​​517,900 mu, and the annual output of coconut fruits is about 223 million.
More than 2 million people in the province are directly or indirectly engaged in the coconut industry, with a total annual output value of over 200 100 million yuan
.

"Although the coconut industry is very hot, basic research on coconuts is relatively backward
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To analyze some important biological phenomena and problems, the first step is to obtain a high-quality genome
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The scientific research team used three-generation and Hi-C sequencing technologies to assemble and obtain coconut reference genomes at the chromosome level of the tall coconut and the short coconut
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Through the comparative analysis of coconut genome with water lily and oil palm, the scientific research team revealed that coconut had two genome-wide doubling events, one of which was unique to palm family
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"The palm family to which coconuts belong is one of the relatively ancient groups of monocots.
It is an ideal species for studying the chromosome evolution of monocots and the differentiation of ancient plants
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The research team used the comparative analysis of the high-quality coconut genome with the genomes of monocotyledonous plants such as purple pineapple and pineapple.
Based on the telomere-centered chromosome reconstruction theory and model, the karyotype of monocot ancestors containing 10 chromosomes was reconstructed.
The karyotype of 5 or 7 chromosomes reported previously has stronger evidence support; and based on this karyotype, the evolution process of 16 chromosomes of the coconut genome is further deduced
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The above research results are helpful to deeply understand the karyotype changes of monocotyledons and even the evolutionary course of angiosperms
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Solve the mystery of coconut height

Coconuts are mainly divided into two subgroups: tall species and short species
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The difference is so great, what determines the difference in plant height between tall coconuts and short coconuts?

"The most interesting thing about this result is that we used genome-wide association analysis combined with biochemical, molecular, and physiological methods to clone the key gene that controls the height of coconut-the GA20ox gene located on chromosome 12.

We also found that this gene is actually the same as that of rice.

The "Green Revolution" gene has extraordinary significance for human beings
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"Combined with the above results, it shows that during the subspecies differentiation process of coconut about 4 million years ago, a
" green revolution " similar to the semi-dwarf breeding process of rice, corn and other crops occurred .

The coconut industry has a broad prospect, but the number is not enough.
A very important reason is that coconuts have a long growth cycle and it is difficult to carry out large-scale breeding
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It takes 8 to 10 years for tall coconuts to bear fruit, and 3 to 5 years for short coconuts
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If the conventional hybrid breeding technology is adopted, it may take several generations and decades to complete the selection and breeding of a variety
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"With this plant height trait control gene, we can develop molecular markers to select dwarf coconuts that are more convenient for picking in advance, which can save a lot of time and resources, greatly speed up the breeding process, and promote the faster development of the coconut industry
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" China Wang Hui, deputy director of the Coconut Research Institute of the Academy of Tropical Agricultural Sciences, told China Science Daily
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Analysis of key traits is of great significance

In addition to tall and short coconuts, there are other different traits.
For example, the cellulose content of tall coconut fruits is relatively high, and the cellulose content of short coconut fruits is low
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"High-species coconuts are closer to wild coconuts.
We speculate that coconuts on island countries in tropical regions spread to other areas through ocean currents, and fiber content is an important factor in whether it can drift over.
This trait is closely related to the evolution of coconuts
.
" Shou Chuang said
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In fact, the size of the original coconut is very small.
For example, melon seeds and coconut are only as big as dates.
In order to float over, the fiber is made longer and more through natural evolution.
The high cellulose is good for the coconut to float on the water, and the cellulose content is not much.
The coconut fruit sank into the sea
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The scientific research team used multi-omics and cytology to analyze this phenomenon
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"Fiber is mainly composed of lignin and cellulose.
We mainly focus on these two aspects, paying attention to all the genes in the synthesis pathway of lignin and cellulose, to see if there is a difference in the expression of these genes between tall coconuts and short coconuts.

The analysis results show that the difference is indeed very large.
The expression of related genes is very high in tall coconuts and very low in dwarf coconuts
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” Xiao Yong introduced
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This time they initially found the sites and genes that control cellulose synthesis
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The so-called "fish and bear's paw cannot have both
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" Xiao Yong said that if the cellulose content is too high, the volume in the middle of the husk will be very small, and the coconut meat and coconut milk inside will also be reduced
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In the beginning, coconuts with greater cellulose content were naturally selected.
With the subsequent development of artificial selection, coconut varieties with more flesh and juicy were gradually produced
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In addition to plant height and fiber, the research team also analyzed the genetic basis of key traits such as salt tolerance and lipid content in tall coconuts and short coconuts
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"After digging out the key genes of these traits, we can build a molecular breeding system in the next step, accelerate the pace of breeding, and make a huge contribution to the industry
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We can also'loan' the genes that determine excellent traits, for example, we can put salt-tolerant genes in It is applied to other crops to improve the salt tolerance of crops and contribute to the genetic improvement of other varieties
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" Wang Hui said
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"The lauric acid in coconuts is currently the highest in plants recognized by humans, and lauric acid is also an important raw material for cosmetics
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Deciphering the molecular mechanism of coconut lipid synthesis and regulation is conducive to extending the coconut industry chain
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" Wang Shouchuang Said
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Related paper information: https://doi.
org/10.
1186/s13059-021-02522-9