Rhododendrons have to "go down", and even more to "scent"

Rhododendrons have to "go down", and even more to "scent"

Rhododendrons have to "go down" and more fragrant

Rhododendron is a horse silver flower of the subgenus horse silver flower
.

Photo courtesy of Wang Xiuyun

 Rhododendron is a horse silver flower of the subgenus horse silver flower

However, although China is a big country with wild resources of azaleas, its research started relatively late
.

In recent years, domestic horticultural scientific research workers have begun to explore continuously, striving to make a world of azaleas on the world stage

Recently, the Institute of Landscape Architecture of Zhejiang University and the Kunming Institute of Botany of the Chinese Academy of Sciences have carried out genome sequencing on Rhododendron subgenus Rhododendron, obtaining high-quality genomes, and revealing the low-altitude adaptability of Rhododendron and the related floral fragrance.
Synthetic pathways and genes have important guiding significance for the domestication of alpine plants and the breeding of flowers
.

Related results were published in "Journal of Plant Biotechnology"

High-quality genetic makeup is an important reference

High-quality genetic makeup is an important reference

Rhododendron, also known as Azalea, Manshanhong, and Pomegranate, is the general name of rhododendrons in the Rhododendron family.
It has a wide variety of species and is a large genus of woody plants
.

There are more than 1,000 species of azaleas in the world, distributed in Europe, Asia and North America, especially in Asia, with 850 species

"There are more than 500 species native to China, especially concentrated in the Hengduan Mountains of Yunnan, Tibet, and Sichuan.
It is the birthplace and distribution center of azaleas in the world
.

" Researcher Wang Xiuyun introduced in an interview with "China Science News"

Rhododendrons, once rarely visited by people, were introduced to various parts of the world by "plant hunters" from the West in the 18th century.
Rhododendrons began to enter Western gardens and gradually occupy an important position
.

Especially in the United Kingdom, there are azaleas in small street courtyards, porches to large and small manors, and the whole season of splendor is used to embellish the colorful spring

Rhododendron is known as the "flower in the west".
In recent years, it has been widely used in urban and rural landscaping, landscaping, and potted viewing, which has promoted the development of the domestic azalea industry
.

However, there is still a long-term problem of a single application variety, and the domestic azalea breeding is still in its infancy

Therefore, it is very important to make full use of our country's rich wild resources and find out its genetic background
.

"We use the representative species of Rhododendron subgenus Cynanchum as the sequencing material.
This is a very representative plant and is of great significance to the research on the adaptability of Rhododendron
.

" Corresponding author of the paper, Institute of Landscape Architecture, Zhejiang University Professor Xia Yiping told China Science Daily

        Photo courtesy of Ma Yinhua Xia Yiping

Photo courtesy of Ma Yinhua Xia Yiping

Although the sequencing technology has been advancing rapidly, there are still some difficulties in assembling the genome of Ma Yinhua
.
"Because the heterozygous rate of Ma Yinhua is estimated to be about 1.
55%, it belongs to the highly heterozygous genome.
We have been exploring the assembly parameters for a long time and have made great efforts in genome annotation
.
" The co-corresponding author of the paper and the Kunming Plant of the Chinese Academy of Sciences Researcher Zhang Chengjun of the institute said in an interview with "China Science Daily"
.

In the end, overcoming many difficulties, they sequenced and assembled a high-quality Genome of E.
elegans 549Mb, contig N50 was 1.
2Mb, chromosome loading rate was 99.
05%, 41264 genes were annotated, and genome annotation completeness reached 96%
.

"The quality of the genome obtained this time is very high, and it is one of the high-quality genomes in the Rhododendrons
.
" Xia Yiping said, providing an important reference for similar research at home and abroad
.

Finding the reason for the difficulty of "going down the mountain"

Finding the reason for the difficulty of "going down the mountain"

The genus Rhododendron can be roughly divided into two categories: high-altitude rhododendrons and low-altitude rhododendrons.
High-altitude rhododendron species account for about 85%, while low-altitude rhododendrons are more common among ordinary people
.

"The high-altitude rhododendron blooms beautifully, and there should be more room for development, but it is facing the dilemma of'going down the mountain'.
Although previous studies have been carried out, the high-altitude rhododendron has not been transplanted to low-altitude areas.
A large-scale success story for the country
.
” Xia Yiping said.
For example, Rhododendron cuckoo can't be used in cities, even Kunming, at an altitude of 2,000 meters, can't be planted
.

In the application of urban greening, azalea is an important decorative resource, which plays an important role in enriching the ecological diversity of urban green space system
.
Xia Yiping pointed out that Rhododendron has poor "heat resistance" ability.
With global warming, it cannot survive the hot summer in cities, and it is difficult to adapt to the low-altitude climate environment, which severely restricts the diversity of the application of Rhododendron garden forest
.

Not only that, in Xia Yiping’s view, the problem of rhododendrons’ "cold tolerance" must be solved.
Many low-altitude rhododendrons cannot go to the north.
For example, the spring azaleas and the hairy azaleas cannot survive in North China, and these are very good for urban greening.
Resources
.

Breaking the "boundary" has become a top priority
.
In order to explore the molecular mechanism of adaptability, they first selected two of the most typical representatives: Rhododendron mongolica and Ma Yinhua
.
Later, because the variability of Muntjac rhododendron was too high, and the traits of the horse silver flower were relatively stable, the team finally determined the horse silver flower as the research object
.

"The subgenus Ma Yinhua belongs to the low-altitude rhododendron group, but it has many similarities with high-altitude rhododendrons in phenotype.
For example, it has leaf leathery and evergreen characteristics similar to the high-altitude group.
It is a very good research material.

"Wang Xiuyun said
.

By conducting a genome comparison analysis with the sequenced high-altitude Rhododendron lantana and Rhododendron rotundifolia, they found that the expanded gene family of the horse silver flower was significantly enriched in multiple stress response pathways such as biotic and abiotic stress.
Among them, the transcription factor NAC gene family expanded It may play an important role in the adaptability of Ma Yinhua to low altitude
.

Xia Yiping added that high-altitude rhododendrons such as Lantana camara and Rhododendron rotundifolia cannot adapt to the adversity of low altitude because they do not have such an evolutionary process
.

In addition, further analysis showed that tandem replication is the main way for the horse silver flower to respond to gene expansion under stress
.

"These findings have guiding significance for the domestication of high-altitude rhododendrons, and are of great value to the urban application of rhododendrons.
They also provide important references for other woody plant research
.
" Xia Yiping said
.

The Secret of "Fragrance and Not Fragrance"

The Secret of "Fragrance and Not Fragrance"

Rhododendrons are loved by people for their various features, colorful flowers, and a wide range of varieties
.
However, almost none of the currently cultivated rhododendrons has a floral fragrance, resulting in the lack of this important ornamental trait
.

“Most species in the subgenus Masilica have floral fragrance, which is a good material for studying the evolution of rhododendron fragrance
.
" Zhang Chengjun said that through detailed analysis of the scent of Masilica, terpenoids are its important floral fragrance components
.

 Photo courtesy of Ma Yinhua and Wang Xiuyun

Photo courtesy of Ma Yinhua and Wang Xiuyun

"Terpenoids are catalyzed and synthesized by terpene synthase (TPS).
We found that the TPS gene family of E.
sylvestris is significantly expanded, more than other rhododendrons, especially the b-type TPS has a higher expression abundance
.
" Wang Xiuyun introduced, They tested two highly expressed TPS and found that their synthetic substances are very consistent with the two most important synthetic substances of horse silver floral fragrance, indicating that these two genes are the key genes for the synthesis of floral fragrance
.

There is another bright spot in this result.
The team found that TPS-b is not a monoterpene synthase as traditionally thought.
According to its different location, it can synthesize monoterpenes or sesquiterpenes
.
In vitro analysis of TPS-b enzyme activity showed that TPS-b can not only use GPP as a substrate to catalyze the synthesis of monoterpenes, but also use FPP as a substrate to synthesize sesquiterpenes; b mainly synthesizes monoterpenes, and TPS-b, which is located in the cytoplasm, mainly synthesizes sesquiterpenes
.

"Moreover, through the evolutionary analysis of different azaleas, we found that compared with other azaleas, Ma Yinhua differentiated earlier, but with less genetic variation, showing a conservative evolutionary form
.
" Wang Xiuyun said, which also confirmed their previous Views derived from morphology
.

The evolutionary analysis of the homologous genes of TPS-b in Rhododendron has proved that the fragrance of Rhododendron is not obtained after differentiation from other Rhododendrons, but that other Rhododendrons have lost their fragrance due to the loss or fragmentation of the TPS gene during the evolution process.

.

"By grasping the molecular mechanism of rhododendrons producing floral fragrance, we can cultivate rhododendrons with floral scent traits.
In the future, not only will the garden be full of spring, but the fragrance of flowers will also be uncontrollable.
The fragrant rhododendrons will be more in line with the Chinese.
Aesthetic interest
.
" Xia Yiping said
.

In Zhang Chengjun's view, the genome they assembled this time basically reached the international "gold standard
.
" "With this high-quality genome, it will lay a solid foundation for our future variety identification and molecular marker-assisted selection and breeding, and it will also better protect the intellectual property rights of new plant varieties
.
"

"Next, the team will carry out directional breeding research, find the key'heat-tolerance' and'cold-tolerance' regulatory genes, and directly use gene editing to cultivate more widely adaptable azaleas, which will help azaleas in urban landscaping.
Open up broader development prospects
.
" Xia Yiping said
.

Related paper information:

https://doi.
org/10.
1111/pbi.
13680