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Directed editing of the two hormone systems "flowering element" and "gibberellin" can boost the "agricultural revolution"
World Agrochemical Network Chinese website reports: Thousands of plants can produce fruits, seeds and other edible parts, but in the world, only a few hundred kinds of plants are cultivated by humans, and human survival and reproduction only depend on dozens of crops. These major food crops have undergone drastic phenotypic changes during human domestication, making them more and more in line with human production needs, which we call the "agricultural revolution". The Agricultural Revolution brought about an increase in food production and allowed crops to be grown on a large scale. In the face of the increasing population problem, if we can speed up the agricultural revolution and let those untapped plants come to people's table, it will undoubtedly bring more food sources to human beings.
On September 5, 2019, Science magazine published an online article co-authored by Prof. Yuval Eshed from the Weizmann Institute of Science in Israel and Prof. Zachary B.Lippman from the Cold Spring Harbor Laboratory in the United States. , a review article titled "Revolutions in agriculture chart a course for targeted breeding of old and new crops". They proposed targeted editing of two hormone systems, "flowering hormone" and "gibberellin", and applied them to new and old crops, which will meet the future dietary needs of human beings and promote sustainable agricultural development. The two major hormone systems, Florigen, which controls flowering, and Gibberellin, which controls plant shape, have driven the agricultural revolution. Modification of these two hormone systems resulted in improved plant shape, including faster ripening, concentrated flowering and fruit set, and lower plant height (lodging resistance).
Plants begin to flower when the level of "Anthocyanin" is high enough to stimulate the flowering of terminal buds, and the newly formed vegetative buds are temporarily inhibited by the locally produced "Antiflorin" signal. The first "anti-flowering" signal to be discovered came from studies of the tomato self pruning (sp) mutant, a rare natural variant discovered in American farmland in the 1820s. In vegetable fields full of tomatoes, the mutant was short in height and had few branches, as if it had been pruned. It enabled the large-scale production of tomatoes and transformed the agricultural landscape of California's Central Valley (Fig. 2A). In simple terms, the mutation of the sp gene disrupts the "anthocyanidin" signal, relieves the inhibition of "anthocyanidin" activity by "anthocyanidin" in lateral buds, and enables tomato from an infinite cycle of vegetative growth and reproductive growth to a continuous one. Concentrated flowering resulted in tomato varieties that simultaneously bloomed and produced fruit on a large scale, enabling tomato applications in agricultural production. Similar benefits were brought about in the mutant of the homologous gene in soybean (determinate stem, dt1) and in the sp mutant in cotton (Fig. 2B; Fig. 2C).
The "gibberellin" hormone system regulates plant height. After being synthesized through a multi-step complex pathway, the active gibberellin is sensed by the intracellular receptor Gibberellin Insensitive Dwarf 1 (GID1), which in turn directs the degradation of DELLA, a growth inhibitory protein. More than 50 years ago, the introduction of gain-of-function DELLA mutations in wheat and mutations in the gibberellin biosynthesis gene in rice resulted in a shorter plant height phenotype. Breeders use these "dwarfing genes" to make crops shorter in height, avoiding lodging and yield losses that result from unrestricted plant growth through the use of chemical fertilizers. Wheat is a hexaploid plant, and the homologous gene mutation of the Reduced height-1 (Rht-1) gene encoding the DELLA protein can inhibit gibberellin signaling to varying degrees. Among them, the semi-dwarf Rht-B1b and Rht-D1b mutations were found in most current wheat lines (Fig. 3). The discovery of these mutants doubled the production of wheat and rice during the Green Revolution of the 1870s, providing food for hundreds of millions of people.
Using the CRISPR-Cas genome editing system, breeders can more rapidly target and alter genes to obtain desired mutants. At the same time, genome editing has also accelerated the domestication of crops that have not been widely exploited. For example, Lippman's research group used gene editing technology to improve the tomato's distant relative, "girl fruit", in terms of branch structure, flowering and fruit size.
The authors propose that the targeted generation of genetic variation in the core components of the two hormonal systems "flowering hormone" and "gibberellin" could lead to broader phenotypic variation. Introducing this breeding model into traditional and underutilized crops can meet future human dietary needs and sustainable agricultural development.
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