Recently, new progress has been made in the cloning and evolution of cold tolerance genes at the booting stage of rice completed by the Institute of Grain Making, Hubei Academy of Agricultural Sciences in cooperation with China Agricultural University and other units, and the research result article "Stepwise selection of natural variations at CTB2 and CTB4a improves cold duration adaptation domestication of japonica rice" was published online in full in "New phytologist" (IF: 8.51). In this study, a new rice booting stage cold tolerance gene CTB2 was cloned, and the gradual selection of natural variants of CTB2 and CTB4a improved the cold adaptability of japonica rice. It was found that cold tolerance japonica rice originated in Kunming, Yunnan Province, China.
Rice is a cold-sensitive crop originating from the tropics or subtropics, and encountering low temperatures during the booting stage can lead to the inability of rice to develop normally and severely reduce yield. In this study, a segregating population was constructed using near-cold tolerance isogenic lines, and on the basis of linkage mapping, genome-wide association analysis was further performed using the booting stage cold tolerance phenotype of 54 japonica and 67 indica germplasm resources to mine a new cold tolerance gene CTB2. CTB2 encodes a glucosyltransferase that is highly expressed in the tapetum, pollen grains, and anthers. Under low temperature stress, CTB2 can maintain the permeability of cell membrane, protect pollen grain and pollen outer wall structure, and finally improve the cold tolerance of rice by affecting the contents of sterol glycosides and acetylated sterol glycosides.
CTB4a is an important rice booting stage cold tolerance gene previously cloned by the team (Zhang et al., 2017), and this study analyzed and found that wild rice does not contain functional variants of CTB4a, and its cold tolerance alleles are new variants domesticated in cold environments, mainly distributed in high altitude and high latitude regions; while CTB2 has four haplotypes, one of the dominant haplotype SNPs (A) showing strong cold tolerance, which originates from common wild rice in China and has been significantly artificially selected during the cold adaptation domestication of japonica rice, gradually spreads to high latitudes, and finally enhances the cold tolerance of rice together with newly produced local CTB4a variants. It makes the planting area of rice extend from low altitude to high altitude, and finally to northeast China at high latitude, which plays an important role in the development of rice in cold areas.
This study found that during japonica rice domestication, its cold tolerance could be improved by stepwise selection for existing and new variants. This study not only provides an important gene resource for rice cold tolerance breeding, but also provides another theoretical example for plant adaptive evolution. The results are of great significance to effectively ensure the high yield and stable yield of rice under low temperature or cold planting conditions, and promote the further planting development of rice to high altitude and high latitude areas.
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