Seed dormancy is an important survival tool for plants as it allows them to cope with weather conditions that are not conducive to survival. At the same time, excessive dormancy can reduce cultivation time. In response, farmers often plant rice and wheat cultivars with low dormancy to achieve a higher and more uniform emergence rate after sowing. Unfortunately, this practice has led to an undesirable global production problem called pre-harvest sprouting (PHS), which dramatically reduces both yield and grain quality. In rice, PHS damages about 6% of conventional rice acreage and up to 20% of hybrid rice acreage due to long-term rainy weather during the harvest season in southern China. In bread wheat, the direct economic loss caused by PHS approaches $1 billion per year.
With global climate change, PHS are occurring more frequently. For example, major wheat producing areas, especially the winter wheat regions of the Middle and Lower Yangtze River Valley and the Yellow and Huai Valleys in China, experienced serious PHS problems in 2013, 2015 and 2016. Heavy rainfall in 2016 and 2020 also led to serious PHS problems in the rice-growing areas of the middle and lower Yangtze River valley in China.
In an effort to solve this problem, researchers led by Profs. CHU Chengcai and GAO Caixia of the Institute of Genetics and Developmental Biology (IGDB) of the Chinese Academy of Sciences (CAS) recently revealed that the SD6/ICE2 The molecular module controls rice seed dormancy and has great potential to improve PHS tolerance of rice and wheat.
The study was published in Natural genetics December 5.
In this study, researchers used a set of single-segment chromosome substitution lines derived from a cross between low dormancy japonica rice cultivar Japanesebare and strong dormancy out rice cultivar Kasalat to identify a gene, named Seed dormancy 6 (SD6), which contributes to rice seed dormancy.
Researchers found that SD6 and its interacting partner ICE2 antagonistically control rice seed dormancy by regulating abscisic acid (ABA) homeostasis. Specifically, SD6 directly promotes the expression of the ABA catabolism gene ABA8OX3 and indirectly inhibits the expression of the ABA biosynthetic gene NCED2while ICE2 acts in the opposite way.
Temperature has a major effect on the strength of seed dormancy. The researchers revealed that the SD6/ICE2 The molecular module controls the dormancy of rice seeds depending on the temperature: SD6 is regulated to initiate seed germination when seeds are at room temperature. However, at low temperature, SD6 is down-regulated while ICE2 is up-regulated to maintain seed dormancy.
By editing SD6 in three rice cultivars, T619, Wu27 and Huai5, researchers found that genetic editing of SD6 could be a quick and useful strategy to improve PHS tolerance in rice. Interestingly, the edition of the TaSD6 The wheat variety Kenong199 gene also greatly improved the PHS resistance of wheat, indicating that the SD6 The gene is functionally conserved in controlling seed dormancy in rice and wheat.
In summary, SD6 and ICE2 regulate seed dormancy by adjusting the ABA content of seeds according to temperature. In this way, they help the seeds overcome natural seasonal changes and ensure successful reproduction. For this reason, SD6 may be a potent target for improving PHS resistance of cereals under field conditions.
This work was supported by grants from the G2P Project of the Ministry of Science and Technology of China, the CAS Strategic Priority Research Program, the CAS Frontier Sciences Key Research Program, and the National Natural Science Foundation. from China.
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Antagonistic control of seed dormancy in rice by two bHLH transcription factors
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