How 120 days of space travel, rice and Arabidopsis thaliana changed

Handover ceremony
of the third batch of space science experiment samples of the manned space station.
Photo courtesy of Chinese Academy of Sciences

Picture of spatial rice native rice and regenerated rice, showing the phenotype
of spatial rice ear with the shell open.
Photo courtesy of Chinese Academy of Sciences

【Frontier of Science and Technology】

On December 4, rice and Arabidopsis thaliana seeds, which experienced a full life cycle in space for 120 days, returned smoothly with the Shenzhou 14
spacecraft.
This means that China has successfully carried out the whole life cycle cultivation experiment
of rice from seed to seed for the first time in the world.
According to reports, the scientific name of this study is "The molecular mechanism of flowering regulation of higher plants under microgravity conditions", which is undertaken by the team of Zheng Huiqiong, Center for Excellence in Molecular Plant Science, Chinese Academy of Sciences
.
So, why this experiment? And what are the gains?

Why send rice and Arabidopsis thaliana into space

Zheng Huiqiong introduced that rice is the main food crop for mankind, feeding nearly half of the world's population, and is also the main candidate food crop
for future manned deep space exploration life support systems.
The use of space microgravity for rice breeding is one of the important directions of
space botany research.
"Seeds are not only food for human beings, but also the carrier for reproducing the next generation of plants, and if human beings want to survive in space for a long time, they must ensure that plants can complete the generation of space and successfully reproduce seeds
.
" However, previously, only the cultivation of Arabidopsis thaliana, rape, pea and wheat from seed to seed had been completed in space, while rice, the main food crop, had not been able to complete the full life cycle cultivation
in space.
”

The model plant Arabidopsis thaliana mainly undertook the study
of the "flowering" part.
Zheng Huiqiong said: "Flowering is the prerequisite for seeding, and we used the model plant Arabidopsis thaliana to systematically study the effect of
space microgravity on plant flowering.
”

What happened to rice and Arabidopsis thaliana on their space journey

Zheng Huiqiong introduced that the on-orbit experiment started the experiment from the injection of nutrient solution on July 29, 2022, and ended the experiment on November 25, 2022, and completed the cultivation experiment of the whole life cycle of Arabidopsis thaliana and rice seed germination, seedling growth, flowering and seeding
.
During this period, astronauts conducted three sample collections in orbit - samples from rice at the gestational stage on September 21, Arabidopsis thaliana during flowering on October 12, and samples from rice and Arabidopsis thaliana seed maturity on November 25
.
After collection, samples at the flowering or pregnant stage were stored in a -80°C cryogenic storage cabinet, and seed ripening samples were stored in a 4°C cryogenic storage cabinet
.

Zheng Huiqiong said that three space experiments were mainly completed this time
.
First, the whole life cycle of rice cultivation experiments from seed germination, seedling growth, ear extraction and seed setting was completed on track, and the images were obtained for analysis
.
Second, after the completion of cutting, the spatial regeneration rice was successfully cultivated and produced mature seeds (two stubbles).

Third, the image observation and analysis of the spatial microgravity response of Arabidopsis thaliana seed germination, seedling growth and flowering key genes regulated by different three biological clocks were completed in orbit, and samples were collected in orbit
.

The samples have now been transferred to the Innovation Center of Excellence in Molecular Plant Sciences of the Chinese Academy of Sciences in Shanghai for further analysis
.

What are the preliminary findings of the experiment

Through the analysis of the images acquired in space and the comparison with the ground control, it was found that spatial microgravity had the effects
of various agronomic traits of rice, including plant height, tillering number, growth rate, water regulation, light response, flowering time, seed development process and setting rate.
Scientists have made some initial findings:

First, it was found that the plant type of rice became looser in space, mainly because the angle between stems and leaves became larger.
Dwarf rice became shorter, and the height of tall rice was not significantly affected
.
In addition, the spiraling movement of rice leaf growth controlled by the biological clock is more prominent
in space.

Secondly, the flowering time of the rice space is slightly earlier than that of the ground, but the filling time is extended by more than 10 days, and most of the shells cannot be closed
.
"Flowering time and shell closure are important agronomic traits in rice, both of which play an important role in ensuring sufficient reproductive growth of plants to obtain high-yielding and high-quality seeds, which are regulated by gene expression and will be used to return samples for further analysis
," said Zheng.
”

Again, regenerative rice experiments are carried out in space and seeds of regenerated rice are obtained
.
Zheng Huiqiong said: "Two rice ears can be regenerated after 20 days from cutting, indicating that it is feasible to regenerate rice in a closed environment with limited space, which provides new ideas and experimental evidence
for the efficient production of space crops.
" This technology can greatly increase the yield of rice in the volume, and it is also the first regenerative rice technology
in the world to be tried in space.
”

Finally, for the first time, the key genes of the space circadian clock regulating photoperiod flowering were studied
.
Using genetic mutation and transgenic methods, three Arabidopsis thaliana with different flowering times were constructed: early flowering, delayed flowering and normal flowering (wild type).

Zheng Huiqiong introduced that through the observation and analysis of the growth and development of Arabidopsis thaliana in space, it was found that the response of key genes of flowering to microgravity was significantly different from that of the ground, and the flowering time of Arabidopsis thaliana that flowered early on the ground was also greatly extended
under microgravity conditions.
"In addition, after the mutation of the biological clock gene, the hypocotyl of Spatial Arabidopsis thaliana was over-elongated, indicating that the expression of Circadian Clock gene is very important for maintaining the normal morphology of Arabidopsis thaliana growth in space and adapting to the space environment, and providing a new direction
for the future use of modified flowering genes to promote plant adaptation to the space microgravity environment.
" The follow-up research team will further use the returned materials to further analyze
the molecular basis of Arabidopsis thaliana adaptation to the space environment.
”

(Edited by Li Chuang)