How Rice and Arabidopsis Change After 120 Days of Space Travel

On December 4, rice and Arabidopsis seeds that had gone through a full life cycle of 120 days in space returned to Earth with the Shenzhou XIV spacecraft. This means that my country has successfully carried out the first rice cultivation experiment from seed to seed in the world. According to reports, the scientific name of this study is "Molecular Mechanism of Flowering Regulation of Higher Plants under Microgravity Conditions", which was undertaken by Zheng Huiqiong's team at the Center for Excellence in Molecular Plant Sciences of the Chinese Academy of Sciences. So, why do we need to conduct this experiment? What are the gains?

Why send rice and Arabidopsis to 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 the life support system of future manned deep space exploration. Using space microgravity to breed rice is one of the important directions of space botany research. "Seeds are not only food for humans, but also the carrier for breeding the next generation of plants. If humans want to survive in space for a long time, they must ensure that plants can complete the alternation of generations in space and successfully reproduce seeds. However, the international community has only completed the cultivation of Arabidopsis, rapeseed, peas and wheat from seeds to seeds in space, while the main food crop rice has not been able to complete the cultivation of the entire life cycle in space before."

The model plant Arabidopsis thaliana mainly undertook the research on the "flowering" part. Zheng Huiqiong said: "Flowering is the prerequisite for seed production. We used the model plant Arabidopsis thaliana to systematically study the effects of space microgravity on plant flowering."

What happened to rice and Arabidopsis during their space journey?

Zheng Huiqiong introduced that the on-orbit experiment started with the injection of nutrient solution on July 29, 2022, and ended on November 25, completing the cultivation experiment of the entire life cycle of Arabidopsis and rice seed germination, seedling growth, flowering and seeding. During this period, the astronauts collected samples three times on orbit - rice samples at the booting stage on September 21, Arabidopsis samples at the flowering stage on October 12, and rice and Arabidopsis seeds at the maturity stage on November 25. After collection, the flowering or booting stage samples were stored in a -80℃ low-temperature storage cabinet, and the seed maturity stage samples were stored in a 4℃ low-temperature storage cabinet.

Zheng Huiqiong said that this time, three space experiments were mainly completed. First, the cultivation experiment of rice from seed germination, seedling growth, heading and seed setting was completed in orbit, and the images were obtained for analysis. Second, the space regeneration rice was successfully cultivated after pruning and mature seeds (second crop). Third, the image observation and analysis of the response of Arabidopsis seed germination, seedling growth and flowering key genes regulated by three different biological clocks to space microgravity were completed in orbit, and samples were collected in orbit.

Now, the samples have been transported to the Center for Excellence in Molecular Plant Sciences of the Chinese Academy of Sciences in Shanghai for further testing and analysis.

What are the preliminary findings of the experiment?

By analyzing images obtained in space and comparing them with those on the ground, it was found that microgravity in space has an impact on various agronomic traits of rice, including plant height, tiller number, growth rate, water regulation, response to light, flowering time, seed development process, and fruiting rate. Scientists have made some preliminary findings:

First, it was found that the rice plant shape became looser in space, mainly because the angle between the stem and the leaf became larger; the short-stalked rice became shorter, while the height of the tall-stalked rice was not significantly affected. In addition, the spiral upward movement of rice leaf growth controlled by the biological clock was more prominent in space.

Secondly, the flowering time of rice in space is slightly earlier than that on the ground, but the grain filling time is extended by more than 10 days, and most of the glume cannot be closed. Zheng Huiqiong said: "Flowering time and glume closure are important agronomic traits of rice. Both play an important role in ensuring sufficient reproductive growth of plants to obtain high-yield and high-quality seeds. This process is regulated by gene expression, and the returned samples will be used for further analysis in the future."

Thirdly, regenerated rice experiments were conducted in space and seeds of regenerated rice were obtained. Zheng Huiqiong said: "Two rice ears can be regenerated 20 days after cutting the plant, which shows that regenerated rice is feasible in a small and closed environment. This provides new ideas and experimental evidence for the efficient production of space crops. This technology can greatly increase the rice yield per unit volume, and it is also the first regenerated rice technology tried in space internationally."

Finally, for the first time, the key genes of the space circadian clock regulating photoperiodic flowering were studied. Using gene mutation and transgenic methods, three types of Arabidopsis with different flowering times were constructed, namely: early flowering, delayed flowering and normal flowering (wild type). Zheng Huiqiong introduced that through the observation and analysis of the atlas of the growth and development of Arabidopsis in space, it was found that the response of key flowering genes to microgravity was significantly different from that on the ground. Among them, the Arabidopsis that bloomed early on the ground also greatly extended the flowering time under microgravity conditions. "In addition, after the circadian clock gene mutation, the hypocotyl of Arabidopsis in space was over-elongated, indicating that the expression of circadian clock genes is very important for maintaining the normal morphology of Arabidopsis growing in space and adapting to the space environment. It provides a new direction for the future use of modified flowering genes to promote plant adaptation to the space microgravity environment. The subsequent research team will further use the returned materials to conduct an in-depth analysis of the molecular basis of Arabidopsis' adaptation to the space environment."

(Originally published in Guangming Daily, 2022-12-06, p. 10)