LIFE SCIENCE

Chinese scientists find “switch” to regulate the germination of rice and wheat ears


Spike germination threatens rice yields. Photo by Wang Dehao, researcher of Baihu Crop Seed R&D Center in Anhui Province

Rice, wheat, barley, corn… In recent years, with the global warming, many grains have not yet been out of the field, and the seeds on the ears have crawled with small green seedlings.

“The quality of germinated seeds is reduced, which seriously affects food production. Some over-germinated kernels cannot even be processed for feed, greatly reducing farmers’ income. Chu Chengcai, a researcher at the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences, told China Science News.

Now, Chu Chengcai’s team and Gao Caixia’s team from the Institute of Genetic Development have found a pair of “switches” to regulate the germination of rice and wheat ears, which is expected to provide a solution to the large-scale agricultural losses caused by seed ear germination. The results were published online Dec. 5 in the journal Nature Genetics.

This study is highly regarded by breeding experts. “The relevant research results are exemplary work in recent years at home and abroad to use germplasm resources to mine favorable genes and quickly apply them to breeding innovation, which provides a reference for the effective use of ancient local germplasm resources.” Qian Qian, academician of the Chinese Academy of Sciences and director of the Crop Research Institute of the Chinese Academy of Agricultural Sciences, commented.

“Mr. Suifa Sprout” to find “switch”

In the Institute of Genetic Development, Chu Chengcai has a nickname: “Mr. Sui Fa Sprout”.

Twenty years ago, by chance, Fang Jun, a student of Chu Chengcai, went to Qian Qian, an academician of the Chinese Academy of Sciences, to look at rice materials in the Hangzhou experimental field, and found that it had rained for several days, some rice materials had not been confiscated, and seeds had germinated on ears. Fang Jun took a picture of Chu Chengcai, which he thought was “quite interesting”, which stimulated the desire for research.

But when he started his research, he realized that the actual situation was much more complicated.

In order to accelerate the generation process and ensure that the seeds have consistent germination characteristics in production, breeders have eliminated some dormant materials in the process of breeding in the north and south. With the global warming in recent years, the germination phenomenon of seed spikes has become more and more serious.

The economic losses caused by the germination of spikes to the world are incalculable. According to statistics, in bread wheat alone, the global related losses are as high as 1 billion US dollars per year. Internationally, a special cereal ear germination committee has been set up, and an international conference is held every three years to discuss solutions. However, the problem of spike germination has not been fundamentally curbed.

In the rice cultivation region of southern China, the germination of ears is affected by the rains during the harvest season, resulting in a loss of 6% of the cultivated area of conventional rice, while the loss of hybrid rice is as high as 20% of the cultivated area. “Because hybrid rice is sprayed with gibberellin during the seed preparation process, the seed spike germination phenomenon is more serious.” Yang Yuanzhu, vice president of Longping Hi-Tech and chief expert of rice, said.

Zhang Conghe, deputy general manager and chief technology officer of Quanyin Hi-Tech, also said that the frequent occurrence of adverse weather such as rain or high temperature and drought along the Huaihe River and south of the Huaihe River in China has caused low seed yield, and even frequent rainy weather has caused serious ear germination, resulting in unqualified seed quality. Food security production urgently needs to solve the problem of ear germination of wheat and rice varieties.

The breeder who often dealt with told Chu Chengcai: “People who want to find a study of spike germination can’t find it.” ”

These strengthened Chu Chengcai’s determination to look for genetic “switches” related to seed dormancy.

“Seed dormancy is the phenomenon that seeds cannot germinate under conditions suitable for growth, such as temperature, moisture and oxygen, which is a characteristic common to most higher plants.” Chu Chengcai explained to China Science News.

In fact, scientists have considered screening of strong dormant germplasm resources from wild rice, weed rice and ancient landraces since the 50s of last century, but because this agronomic trait is regulated by a large number of sites, gene cloning faces many bottlenecks, resulting in the production of key genetic resources for ear germination improvement is still very scarce.

Through nearly ten years of efforts, Chu Chengcai’s team finally found a key gene to control rice seed dormancy in Kasalas, a strongly dormant Indian endemic rice variety, which provided a “sharp weapon” for regulating grain ear germination.

“Throttle” and “Brake”

Using the strong dormant variety Casalas and the weakly dormant variety Japan Qing, Drs. Xu Fan, Tang Jiuyou and Cheng Xi successfully cloned a key gene SD6 to control rice seed dormancy from the strongly dormant rice variety Kasalas by constructing a chromosomal single-segment substitution line, and confirmed that SD6 negatively regulates rice seed dormancy. By screening SD6 interaction proteins, the research team also found another rice transcription factor ICE2, and ICE2 is regulating seed dormancy.

“In simple terms, they are like two counterbalanced partners, SD6 is like a ‘throttle’ that promotes seed germination, and ICE2 is like a ‘brake’ that promotes sleep.” Chu Chengcai said metaphorically.

So, how do the molecular modules of these two partners work? Studies have shown that the plant hormone abscisic acid (ABA) is the main internal factor in regulating plant dormant germination. They further found that the SD6/ICE2 molecular module can directly or indirectly regulate the synthesis or metabolism gene of ABA, thereby regulating the ABA content and seed dormancy in rice seeds.

“This discovery sheds light on how crops achieve their real-time balance through synergistic hormone synthesis and metabolism, thereby regulating the intrinsic mechanisms of important agronomic traits.” Qian Qian commented.

Interestingly, the researchers found that the SD6/ICE2 molecular module also evolved a very “smart” environmental adaptation mechanism: SD6 maintains high expression at higher temperatures, while ICE2 maintains low level expression, which is conducive to seed breaking dormancy at higher temperatures for germination; At low temperatures, SD6 expression was inhibited and ICE2 expression was significantly upregulated, which helped seeds to maintain dormancy to avoid low temperature adversity and overwinter smoothly.

“By sensing the temperature changes in the external environment, SD6/ICE2 further controls the ABA content in the seeds, thereby regulating the dormancy intensity of seeds and ensuring that they adapt to the natural season and reproduce successfully.” Chu Chengcai explained.

The research team improved the SD6 gene in rice easy-ear germination varieties Tianlong 619, Wuyun Japonica 27 and Huaidao No. 5 through gene editing technology, and found that the improved rice material had significantly improved its ear germination under the conditions of continuous rainy weather during the harvest period.

“Very useful”

Not only rice, Gao Caixia’s team improved the TaSD6 gene of wheat variety Kenong 199 and found that the germination resistance of wheat ears was greatly improved. This indicates that the function of SD6 gene in controlling seed dormancy in rice and wheat is conserved, and the potential value of other cereal ear germination resistance breeding improvement.

“This study excavated SD6, the trait that controls seed dormancy quantity, from Indian endemic varieties with strong dormancy, demonstrating that rice ear germination can not only be improved through traditional breeding, but also can be quickly created by gene editing technology to germinate rice and wheat germplasm materials.” Qian Qian said that this is a “model” for scientists at home and abroad to use germplasm resources to mine favorable genes and quickly apply them to breeding innovation in recent years.

“So useful!” Many breeder friends said to Chu Chengcai after reading this progress.

“This study will help significantly improve the germination resistance of rice ears in field environments without adverse effects on other important agronomic traits.” It is a boon for us to breed the sterile line of tolerant budding hybrid rice and its varieties. Yang Yuanzhu said.

Zhang Conghe also said that this achievement is of great significance, solving the neck problem in the global seed industry and food production, which will play a good role in promoting the high-quality production of international food security and improving the quality of food, and will promote the safe and high-quality production of wheat and rice seed industry, and further enhance the core competitiveness of China’s seed enterprises.

Talking about the next step, “Mr. Sui Sprout” hopes that the relevant genes can be further verified in other grains such as corn, barley and sorghum.

Chu Chengcai’s team has graduated doctoral students Xu Fan, Tang Jiuyou, associate researcher, Gao Caixia’s team postdoctoral fellow Wang Shengxing, and Chu Chengcai’s team postdoctoral fellow Cheng Xi are the co-first authors of the paper. The research was supported by the G2P Project of the Ministry of Science and Technology, the Strategic Pilot Project of the Chinese Academy of Sciences, the Key Research Project of Frontier Science of the Chinese Academy of Sciences, and the National Natural Science Foundation of China. (Source: China Science News Feng Lifei)

Related paper information:https://doi.org/10.1038/s41588-022-01240-7



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