Shulou(Shulou.com)11/24 Report--

CTOnews.com, December 6 (Xinhua) according to a CCTV news report, the Chu Chengcai team and Gao Caixia team of the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences recently found two "switches" regulating panicle sprouting of rice and wheat, including the key gene SD6 that negatively regulates seed dormancy and the gene ICE2 that positively regulates seed dormancy. The researchers believe that the combination of the two genes is expected to provide a solution to the large-scale agricultural losses caused by seed panicle germination. The results were published online on December 6 in the journal Nature Genetics.

According to the website of the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences, seed dormancy refers to the phenomenon that seeds can not germinate under conditions suitable for its growth (temperature, water and oxygen, etc.). It is an adaptive trait common to most higher plants. In the process of crop domestication, due to more consideration of high yield, high quality, disease and insect resistance and stress tolerance, while ensuring consistent germination characteristics of seeds in production, the retention of moderate seed dormancy is often ignored. as a result, many crops, such as rice and wheat, encounter serious problems of panicle germination in a large area of production, that is, seed germination occurs in the wet climate before harvest in the seed maturity period. Resulting in a huge economic loss of almost no harvest at the last moment of harvest. Therefore, finding the key genes controlling seed dormancy, elucidating the molecular physiological mechanism of seed dormancy regulation and mining their excellent allelic variation are very important to solve the panicle sprouting disaster of rice and other crops.

Panicle sprouting of ▲ rice occurs frequently in many major rice regions in China. The picture is from the website of the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences. However, seed dormancy is an extremely complex agronomic trait, regulated by a large number of quantitative trait loci and significantly affected by a variety of environmental factors. It is difficult to clone the key regulatory genes of seed dormancy, and there is a lack of practical major gene resources in production. In view of this situation, the team of Institute of Genetics and Developmental Biology of Chinese Academy of Sciences successfully cloned a key gene SD6 which controls seed dormancy from Kasalath, and confirmed that SD6 negatively regulates seed dormancy by constructing a high density chromosome single segment substitution line population which can stably detect dormancy loci. By screening SD6 interaction proteins, the team found that another rice transcription factor, ICE2, is regulating dormancy of rice seeds.

Through the experiments of molecular biology, genetics and biochemistry, the team revealed that both SD6 and ICE2 directly target the ABA8ox3 promoter of abscisic acid (ABA) 8-hydroxylase gene, and they recognize the G-box motif or E-box motif on the promoter respectively to achieve reverse regulation of the same target gene. On the other hand, SD6 and ICE2 indirectly regulate the key synthesis regulation gene of ABA, namely 9-cis-epoxy carotenoid dioxygenase gene NCED2, through antagonistic regulation of another transcription factor OsbHLH048. These findings reveal a new regulatory paradigm of hormone balance, that is, antagonistic transcription factor pairs can directly regulate the metabolism of ABA and indirectly regulate the synthesis of ABA, so as to achieve timely and efficient regulation of ABA content to switch seed dormancy and germination.

Seed dormancy is regulated not only by heredity but also by seed environment. Temperature is the most important environmental factor affecting seed dormancy and germination. A warm environment usually accelerates the release of seed dormancy and promotes seed germination, while low temperature keeps seeds dormant. Through this ability to perceive the external environment, seeds can survive adverse environmental conditions, such as low temperatures in winter. The research team found that the SD6-ICE2 molecular module has the characteristics of sensing ambient temperature to regulate seed dormancy: under normal temperature, SD6 gene maintains a high level of expression and plays its function, while ICE2 gene expression is significantly inhibited, thus promoting seed germination; at low temperature, SD6 gene expression is significantly inhibited and ICE2 gene expression is up-regulated, thus keeping seeds in a dormant state. The results show that SD6-ICE2 can dynamically control the content of ABA in seeds by sensing the changes of ambient temperature, so as to regulate the intensity of seed dormancy to adapt to the change of natural climate. This also explains how seed dormancy is used as an adaptive strategy to avoid inappropriate conditions.

The molecular module action model of ▲ SD6 / ICE2 and its application examples the near isogenic lines with SD6 strong dormancy alleles showed excellent panicle sprouting resistance in the field, suggesting that the natural variation locus can be used for conventional breeding improvement of dormancy in high quality rice varieties. At the same time, the SD6 genes of several main rice varieties easy to sprout were improved by gene editing technology, and the team confirmed that the panicle germination of the improved materials under the background of different rice varieties was significantly improved under the condition of continuous overcast and rainy weather during harvest. The improvement of TaSD6 gene of wheat variety Kenong 199 by Gao Caixia's team can also greatly improve the panicle sprouting resistance of wheat, indicating that the function of SD6 gene in controlling seed dormancy in rice and wheat is conservative, that is, SD6 has important application value in the improvement of panicle sprouting resistance in both rice and wheat.

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