Decipher the "map" of peppercorns and find the secret of hemp fragrance

Zanthoxylum bungeanum grown in Fengxian Zanthoxylum bungeanum Experimental Station of Northwest Agriculture and Forestry University
.

Zanthoxylum bungeanum, known as one of the "eight major condiments", is a unique medicinal and edible plant with important economic, medicinal and ecological value
.

Recently, the team of Professor Wei Anzhi of Northwest A&F University has made new breakthroughs in the research of pepper
.

This reference genome provides a valuable model for studying the effects of recent transposon amplification and genome-wide replication events on gene gains and losses and genome reconstruction, and provides a theoretical basis for accelerating the genetic improvement of Zanthoxylum bungeanum
.

Apomixis leads to slow breeding progress

Zanthoxylum bungeanum belongs to the genus Zanthoxylum in the Rutaceae family.
China is the country of origin and main producer of Zanthoxylum bungeanum.
It has a long history of cultivation, extremely rich germplasm resources, and ranks first in the world in terms of output and planting area
.

In recent years, the scale of prickly ash planting has been increasing at a rate of 20% to 30% per year.
The total cultivation area has reached about 25 million mu, with an annual output of about 400,000 tons of dried pepper, forming a huge specialty agricultural product industry with an annual output value of about 30 billion yuan.

.

"The price of pepper has been rising over the years, and it has only gradually stabilized in the last three years.
The price of pepper is relatively high in economic forests, and it is of great significance for poverty alleviation
.

Wei Anzhi pointed out that because Zanthoxylum bungeanum is apomixis, the breeding progress is relatively slow
.

Apomixis is a reproductive method that does not require the union of male and female gametes and directly produces offspring from the mother
.

Large number of chromosomes, high heterozygosity and high repetitive sequences

"Zanthoxylum bungeanum has a large genome, a large number of chromosomes, high heterozygosity and repetitive sequences, which makes assembly difficult
.

Based on this, the research team used Fengjiao as the sequencing material, adopted second- and third-generation sequencing strategies, and combined with Hi-C chromosome conformation capture technology to assemble a pepper chromosome-level reference genome with a size of 4.
23Gb
.

“This is a relatively complete Zanthoxylum bungeanum genome that can be achieved at present, and the size is 10 times that of the sweet orange of the same family.
With
this'map ', more in-depth research can be carried out in the future .

Evolutionary analysis shows that the genetic relationship between Zanthoxylum bungeanum and sweet orange is the most recent.
Their species differentiation occurred approximately 35 million years ago.
After that, Zanthoxylum bungeanum underwent an independent genome-wide replication event approximately 26 million years ago, and reached a value of 6.
4 million.
A transposon explosion occurred a few years ago, and thereafter a series of chromosomal breaks and fusions, which finally formed the current chromosomes
.

Find the key synthetic gene

People love prickly ash, more because of the "numbness" it brings
.

"A lot of research on'hemp' is still on extracting the hemp substance of Zanthoxylum bungeanum, or studying how people perceive the numb taste after eating Zanthoxylum bungeanum.
Some people are also studying the chemical synthesis of hemp, but the biosynthetic research work is scarce.
Few people develop, we use this as a breakthrough
.
" Feng Shijing said
.

The research team used the obtained genomic information, combined with the transcriptome and metabolome, to identify key synthetic genes related to prickly ash, peel color, and aroma components, and analyzed the expression patterns of these genes at different stages of fruit development, and initially mapped The metabolic pathway diagram of the synthesis of the numbing substance of Zanthoxylum bungeanum is shown
.

Sichuan Hanyuan peppercorns Photo courtesy of the interviewee

The planting area of ​​Zanthoxylum bungeanum is very extensive.
At present, the main cultivation areas in China include Sichuan, Shaanxi, Gansu, Shandong, Hebei and other provinces
.
In the process of cultivation, domestication and introduction, Zanthoxylum bungeanum formed many varieties (lines), such as Dahongpao and Xiaohongpao (Xiaohongjiao)
.

Different provenance areas have different climatic conditions and natural environments, which also leads to differences in flavor, numbness and color of pepper from different origins
.
In addition, the branches of the peppercorns have thorns, which affect the efficiency of picking
.

"Everyone wants to breed prickly ash varieties with no thorns, good fragrance, strong hemp flavor, good color, and high yield.
This was a luxury in the past.
Now that we have deciphered the genome'map', molecular breeding can be carried out.
It has realized the integration of thousands of advantages
.
" Wei Anzhi said
.

Related paper information: https://doi.
org/10.
1038/s41438-021-00665-1